Biomedical subjects

C A Maggi

Publications and source records attributed to C A Maggi.

At least 199 records · Page 11Linked to original sources

PubMed1994

Synergistic role of muscarinic acetylcholine and tachykinin NK-2 receptors in intestinal peristalsis.

It is known that tachykinins (substance P, neurokinin A) participate in the excitatory neural pathways subserving peristaltic motor activity in the intestine. The aim of the present study was to elucidate the types of tachykinin receptor (NK-1 or NK-2) involved in peristalsis by the use of receptor subtype-selective antagonists. Peristaltic motility in isolated segments of the guinea-pig ileum was induced by pumping fluid into the oral end of the intestinal segment. By way of the intraluminal pressure the compliance of the intestinal wall during the preparatory phase and the pressure threshold to trigger the emptying phase of peristalsis were recorded. The tachykinin antagonists were used at concentrations that were at least 30 times in excess of the equilibrium dissociation constants which had previously been evaluated with receptor subtype-selective agonists on the guinea-pig ileum circular muscle. The NK-1 selective antagonist CP-96,345 (0.3 microM) had a slight stimulant influence on peristalsis, whereas the NK-2 selective antagonists MEN-10,376 (10 microM), GR-94,800 (0.3 microM) and SR-48,968 (0.1 microM) led to a small inhibition of motor activity. However, when given after exposure of the ileum to a threshold concentration of atropine (5-20 nM) causing little depression of peristalsis, the tachykinin NK-2 receptor antagonists invariably abolished peristalsis. This synergistic interaction was not seen when SR-48,968 was administered after the ileal segments had been exposed to concentrations of hexamethonium, isoproterenol or calcitonin gene-related peptide that by themselves caused a slight inhibition of peristalsis only.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Effect of omega-conotoxin on cholinergic and tachykininergic excitatory neurotransmission to the circular muscle of the guinea-pig colon.

The aim of this study was to compare the stimulus-response characteristics of the cholinergic and tachykininergic excitatory transmission to the circular muscle of the guinea-pig proximal colon and their susceptibility to inhibition by the N-type calcium channel blocker omega-conotoxin (CTX). All experiments were performed in the presence of guanethidine (3 microM), indomethacin (10 microM), L-nitroarginine (L-NOARG, 30 microM) and apamin (0.1 microM). In the presence of the tachykinin receptor antagonists, FK 888 (10 microM0 and GR 94,800 (3 microM), to block NK1 and NK2 receptors, respectively, electrical field stimulation (EFS) produced frequency-dependent atropine- (1 microM) sensitive contractions. In the presence of atropine (1 microM), EFS produced tachykininergic contractions which were abolished by the combined administration of FK 888 (10 microM) and GR 94,800 (3 microM). The maximal responses produced by cholinergic and tachykininergic neurotransmission ranged between 80 and 100% of the maximal contractile response to 80 mM KCl. The frequency of stimulation, pulse width and voltage required to produce 50% of the maximal cholinergic and tachykininergic contraction were not different from each other, although cholinergic transmission appeared more efficient in producing twitch contractions in response to single pulse EFS. Furthermore, cholinergic transmission was more efficient than tachykininergic transmission in producing contraction in response to short periods of EFS. CTX (0.1 microM for 30 min) produced a large and comparable rightward shift of the cholinergic and tachykininergic frequency-response curve (19 and 17 fold increase in the frequency of stimulation producing 50% of the maximal response, respectively) and markedly depressed (51 and 43% inhibition, respectively) the maximal concentrations response.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗

PubMed1994

Multiple mechanisms in the smooth muscle relaxant action of calcitonin gene-related peptide (CGRP) in the guinea-pig ureter.

We have investigated the ability of human alpha CGRP (CGRP) to inhibit the electrically-evoked myogenic contractions of the guinea-pig ureter, in comparison with the K channel opener, cromakalim, and the adenylate cyclase activator, forskolin. CGRP (0.1 nM-0.1 microM) produced a concentration-dependent inhibition of the evoked contractions; its action was prevented by the CGRP receptor antagonist, CGRP(8-37) (1 microM), while it was unaffected by the nitric oxide (NO) synthase inhibitor, L-nitroarginine (30 microM). The effect of CGRP was antagonized in a noncompetitive manner (depression of Emax, no change in EC50) by glibenclamide (1-10 microM), a blocker of ATP-sensitive potassium channels (KATP). A substantial fraction of the inhibitory effect of CGRP was glibenclamide-resistant, however. Glibenclamide also blocked the inhibitory action of cromakalim (0.1-10 microM) without affecting the inhibition produced by forskolin (0.1-30 microM). When tested in a low-K medium (extracellular K reduced from 5.9 to 1.2 mM), the inhibitory effects of CGRP, cromakalim and forskolin were enhanced. The inhibitory effect of forskolin was partly antagonized by glibenclamide when tested in a low-K medium. CGRP (0.1 microM), cromakalim (3 microM) and forskolin (10 microM) inhibited the contractile response to KCl (80 mM), which is characterized by a distinct phasic and tonic component: cromakalim selectively inhibited the phasic response to KCl with CGRP and forskolin inhibited both components. The inhibitory effect of CGRP on the phasic contraction to KCl was partly glibenclamide-(1 microM) sensitive, while that on the tonic contraction was glibenclamide-resistant. The inhibitory action of forskolin on both components of the response to KCl was unchanged by glibenclamide.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

PubMed1994

In vivo evidence for the activation of a septide-sensitive tachykinin receptor in guinea pig bronchoconstriction.

Intravenous administration of the undecapeptide [Sar9]substance P (SP) sulfone (1.5 nmol/kg) and the hexapeptide [Glp6,Pro9]SP(6-11) (septide; 0.4 nmol/kg) produced a comparable (about 30-40% of maximal effect) increase of insufflation pressure (bronchospasm) in anesthetized guinea-pigs. The non peptide NK-1 receptor antagonist, (+/-)CP 96,345 and the peptide NK-1 receptor antagonist, GR 82,334 antagonized dose-dependently the response to both agonists. Both antagonists were more potent against septide than against [Sar9]SP sulfone (9 and 4 fold difference in ED50 for (+/-)CP 96,345 and GR 82,334, respectively). These findings indicate that a 'septide-sensitive' mechanism mediates bronchoconstriction in vivo and it influences the estimate of the potency of NK-1 receptor antagonists.

Animals↗

PubMed1994

The behavioral response induced by intravesical instillation of capsaicin rats is mediated by pudendal urethral sensory fibers.

The behavioral response induced by the intravesical instillation of capsaicin has been investigated in catheter-implanted, freely moving, conscious male and female rats. Intravesical instillation of capsaicin (25 nmol/rat in 0.5 ml) evoked an intense licking directed toward the lower abdominal and perineal skin which lasted for 15 min. Capsaicin-induced licking was reduced by systemic capsaicin pretreatment at a dose of 150 mg/kg but not at 50 mg/kg, administered 4 days before the intravesical instillation. Both doses of capsaicin effectively abolished the eye-wiping response to local capsaicin application. The capsaicin-induced licking was preserved (and prolonged) in both male and female animals subjected to bilateral ablation of the pelvic ganglia, 48 h before the intravesical instillation of the irritant. The capsaicin-induced licking was almost abolished by placing a ligature around the proximal urethra (24 h before), in order to avoid the contact of the irritant with the urethra or by previous section of the pudendal nerves (48 h before). One hour intravesical infusion with tetrodotoxin (1 and 10 microM) reduced the amplitude of micturition contractions but did not prevent the licking response evoked by capsaicin. On the contrary, the intravesical infusion of lidocaine (100 mM) abolished both micturition contractions and the capsaicin-induced licking. We conclude that the behavioral response induced by the intravesical instillation of capsaicin is mainly due to the stimulation of urethral afferents travelling within pudendal nerves.

Animals↗

PubMed1994

Synthesis and biological activity of NK1 substance P selective agonists by modifying the methionyl residue.

A series of analogues of substance P, where the Met11 residue was replaced by Glu(OCH2CH3), Glu(OBzl) and Hse(CH3), were synthesized in order to investigate the effect on agonist activity of modifications at the C-terminal residue. The biological activities in the guinea-pig ileum assay (NK1 receptor) and rat [text says rabbit] pulmonary artery (NK2 receptor) indicate that replacement of the SCH3 group of Met11 of substance P by the COOBzl or OCH3 groups favour interaction with the NK1 receptor and increase selectivity towards this receptor subtype.

Amino Acid Sequence↗

PubMed1994

In vivo effects of neurokinin B on rat urinary bladder motility: involvement of tachykinin NK1 and NK2 receptors.

The ability of the selective tachykinin NK1 and NK2 receptor agonists, [Sar9] substance P (SP) sulfone and [beta Ala8] neurokinin A (NKA), respectively, and neurokinin B (NKB) to stimulate urinary bladder contractions was determined in urethane-anaesthetized rats with intact bladder innervation and in animals with acute, bilateral ablation of pelvic ganglia. In addition, tachykinin receptors mediating the response to the agonists were characterized by means of the non-peptide NK1 and NK2 receptor selective antagonists, RP 67,580 and SR 48,968 respectively. In both experimental conditions (normal and ganglionectomized), the three tachykinin agonists induced a dose-dependent increase in intravesical pressure, however reflex bladder contractions were produced by the agonists only in animals with intact bladder innervation. RP 67,580 (10 mumol/kg, i.v.) reduced the response to [Sar9]SP sulfone (50 pmol/rat) in both preparations without modifying the effects induced by the NK2 receptor agonist. On the other hand, SR 48,968 (1 mumol/kg, i.v.) antagonized responses induced by [beta Ala8] NKA (50 pmol/rat) but not those evoked by [Sar9] SP sulfone. In animals with intact urinary bladder innervation, the effect of NKB (50 pmol/rat) was inhibited by SR 48,968 (1 mumol/kg, i.v.) but not by RP 67,580; on the contrary, in rats with ablation of pelvic ganglia, the direct bladder contraction induced by NKB was reduced by RP 67,580 (10 mumol/kg, i.v.) but not by SR 48,968. We conclude that NKB induces reflex and direct bladder muscle contractions by stimulating NK2 and NK1 receptors, respectively.

Animals↗

PubMed1994

Synthesis and biological activity of NK1 tachykinin antagonists not containing D-residues.

A series of analogues of the previously reported NK1 tachykinin antagonist [Orn6, Glu(OBzl)11]-SP6-11-OBzl has been synthesized and tested in order to investigate the effects on antagonistic activity of modifications at the C-terminal residue. The biological activity in the guinea-pig ileum assay (NK1 receptor) indicates that the two aromatic rings introduced in the C-terminal part of the peptide are both essential for the expression of antagonistic activity.

Amino Acid Sequence↗

PubMed1994

Specialization of tachykinin NK1 and NK2 receptors in producing fast and slow atropine-resistant neurotransmission to the circular muscle of the guinea-pig colon.

We studied the relative contribution of tachykinin NK1 and NK2 receptors in producing nonadrenergic noncholinergic excitation of the circular muscle of the guinea-pig proximal colon in response to electrical field stimulation. All experiments were performed in the presence of atropine, guanethidine, indomethacin, apamin and L-nitroarginine. In organ bath experiments, electrical stimulation produced a tetrodotoxin-sensitive frequency-dependent contraction. The NK1 receptor antagonists, FK 888 (1-10 microM) and GR 82,334 (0.3-3 microM) markedly reduced but did not abolish the nonadrenergic noncholinergic response. The NK2 receptor antagonist, GR 94,800 (0.3-3 microM) was partly effective at 3 microM. The combined administration of FK 888 (10 microM) and GR 94,800 (3 microM) or GR 82,334 and GR 94,800 abolished the nonadrenergic noncholinergic contraction. The response to a prolonged period of stimulation (3 Hz for 5 min) was evenly depressed by FK 888 or GR 82,334, while GR 94,800 was more effective in inhibiting the late (87% inhibition) than the peak response (25% inhibition). In the presence of nifedipine (1 microM) a marked inhibition of the nonadrenergic noncholinergic contraction was observed and a time lag was evident between stimulus application and onset of contraction, which showed slow onset and offset kinetics. The nifedipine-resistant nonadrenergic noncholinergic contraction was unaffected by FK 888 or GR 82,334 but was suppressed by GR 94,800. Submaximally effective (1-3 nM) concentrations of substance P and neurokinin A produced distinct patterns of contraction: the response to substance P was fast and declined rapidly toward baseline; the response to neurokinin A was slow and sustained. In the presence of nifedipine, the response to substance P was greatly depressed and became slower in onset; nifedipine did not affect the contraction to neurokinin A but slowed its time-course. In sucrose gap experiments, either a short (10 Hz for 1 s) or a prolonged period of electrical stimulation (3 Hz for 3 min) evoked membrane depolarization, action potentials and contraction: in response to the "prolonged" stimulation, distinct phasic and tonic component of contraction were observed. Nifedipine abolished action potentials and the phasic contraction produced by a short period of stimulation, reduced by about 50% the maximal contraction developed during the prolonged stimulation without affecting the amplitude of the tonic response. In the presence of nifedipine, GR 82,334 (3 microM) blocked the membrane depolarization but did not affect contraction; GR 94,800 (0.1 microM) did not affect depolarization but abolished contraction.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

PubMed1994

Calcitonin gene-related peptide (CGRP) regulates excitability and refractory period of the guinea pig ureter.

Previous studies have indicated that calcitonin gene-related peptide (CGRP), released from the peripheral endings of capsaicin-sensitive primary afferent neurons, may play a role as an inhibitory transmitter in the guinea pig ureter. The aim of this study was to compare the effect of capsaicin desensitization and administration of a CGRP receptor antagonist on the excitability and refractory period of the guinea pig ureter to electrical field stimulation. Electrical field stimulation using a long (5 msec.) pulse width produced phasic contractions of the ureter which were unaffected by tetrodotoxin, that is, were produced through direct excitation of ureteral smooth muscle. Human alpha CGRP (1 to 10 nM.) produced a concentration-dependent transient suppression of the evoked contractions, and its effect was prevented by the CGRP receptor antagonist human alpha CGRP(8-37) (1 microM.). In vitro capsaicin pretreatment (10 microM. for 15 minutes) to block neuropeptide release from peripheral endings of sensory nerves or administration of the CGRP receptor antagonist enhanced the responsiveness of the guinea pig ureter to electrical stimulation. In control ureters, the application of two trains of electrical stimuli failed to produce a second contraction at intertrain intervals greater than 20 seconds. The intertrain interval required to obtain a second contraction averaging 50% of the amplitude of the first response (ITI50) of control ureters was about 50 seconds. In vitro capsaicin pretreatment or administration of the CGRP receptor antagonist reduced the refractory period of the ureter to electrical field stimulation: ITI50 averaged 8.8 and 9.1 seconds after capsaicin or CGRP antagonist pretreatment, respectively. These findings demonstrate that capsaicin pretreatment or blockade of CGRP receptors produced qualitatively and quantitatively similar excitatory effects on ureteral excitability and refractory period and are in general agreement with the idea that CGRP is a primary inhibitory transmitter in guinea pig ureter. Inhibition of motility by CGRP could be important for setting the frequency of ureteral peristalsis and suppression of latent pacemakers to prevent the occurrence of antiperistaltic waves.

Animals↗

PubMed1994

Effect of longitudinal muscle-myenteric plexus removal and indomethacin on the response to tachykinin NK-2 and NK-3 receptor agonists in the circular muscle of the guinea-pig ileum.

1. The effect of removal of the longitudinal muscle-myenteric plexus (LM-MP) and/or indomethacin (10 microM) on the response to the tachykinin NK-2 receptor selective agonist, [beta Ala8]NKA(4-10), or to the NK-3 receptor selective agonist, senktide, was investigated by measuring mechanical activity (isotonic recording) of circular muscle (ring preparation) of the guinea-pig ileum. 2. Indomethacin (10 microM) increased the percentage of ileal rings displaying spontaneous activity, either intact or LM-MP-free. The response to senktide (10 nM and 1 microM) was lower in LM-MP-free than in intact ileal rings, either in the absence or presence of indomethacin. The response to a low concentration (10 nM) of [beta Ala8] NKA (4-10) was enhanced in LM-MP-free rings and by indomethacin. 3. In intact ileal rings, the response to senktide was unaffected by atropine (3 microM) alone or by the tachykinin NK-2 receptor antagonist MEN 10,376 (10 microM) alone while it was reduced by the combined administration of the two antagonists. The response to senktide was greatly reduced by tetrodotoxin (TTX, 1 microM). Senktide-induced contractions (10 nM) were also reduced by the blocker of N-type voltage-sensitive calcium channels, omega-contoxin (CTX, 0.1 microM). 4. In about 30% of preparations tested, an inhibitory response (decrease in spontaneous activity) to 10 nM senktide, was disclosed in CTX-treated intact ileal rings. This inhibitory effect was TTX-sensitive. 5. In LM-MP-free ileal rings, the response to senktide was abolished or reduced by atropine and MEN 10,376, alone or in combination, and was also reduced or abolished by TTX and CTX. 6. The response to [beta Ala8]NKA (4-10) was inhibited by MEN 10,376, in both intact and LM-MP-free ileal rings while it was unaffected by atropine, TTX or CTX. 7. These results indicate that indomethacin pretreatment induces a regular background activity for studying the motor response to tachykinins in the circular muscle of the ileum, probably by blocking the formation of relaxant prostanoids. A further increase in sensitivity to direct smooth muscle stimulation (NK-2 receptor agonist) can be obtained by removal of the LM-MP. The response to NK-3 receptor stimulation is diminished but not abolished by removal of the LM-MP, suggesting that NK-3 receptors are located on neuronal bodies of myenteric neurons, but possibly also at other sites (possibly, nerve terminals).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1994

Comparison of tachykinin NK1 and NK2 receptors in the circular muscle of the guinea-pig ileum and proximal colon.

1. The aim of this study was the pharmacological characterization of tachykinin NK1 and NK2 receptors mediating contraction in the circular muscle of the guinea-pig ileum and proximal colon. The action of substance P (SP), neurokinin A (NKA) and of the synthetic agonists [Sar9]SP sulphone, [Glp6,Pro9]SP(6-11) (septide) and [beta Ala8]NKA(4-10) was investigated. The affinities of various peptide and nonpeptide antagonists for the NK1 and NK2 receptor was estimated by use of receptor selective agonists. 2. The natural agonists, SP and NKA, produced concentration-dependent contraction in both preparations. EC50 values were 100 pM and 5 nM for SP, 1.2 nM and 19 nM for NKA in the ileum and colon, respectively. The action of SP and NKA was not significantly modified by peptidase inhibitors (bestatin, captopril and thiorphan, 1 microM each). 3. Synthetic NK1 and NK2 receptor agonists produced concentration-dependent contraction of the circular muscle of the ileum and proximal colon. EC50 values were 83 pM, 36 pM and 10 nM in the ileum, 8 nM, 0.7 nM and 12 nM in the colon for [Sar9]SP sulphone, septide and [beta Ala8]NKA-(4-10), respectively. The pseudopeptide derivative of NKA(4-10), MDL 28,564 behaved as a full or near-to-full agonist in both preparations, its EC50s being 474 nM and 55 nM in the ileum and colon, respectively. 4. Nifedipine (1 microM) abolished the response to septide and [Sar9]SP sulphone in the ileum and produced a rightward shift and large depression of the response in the colon. The response to [beta Ala8]NKA(4-10) was abolished in the ileum and largely unaffected in the colon. 5. The NK1 receptor antagonists, (+/-)-CP 96,34, FK 888 and GR 82,334 competitively antagonized the response to septide and [Sar9]SP sulphone in both preparations without affecting that to [beta Ala8]NKA(4-10). In general, the NK1 receptor antagonists were significantly more potent toward septide than [Sar9]SP sulphone in both preparations. 6. The NK2 receptor antagonists, GR 94,800 and SR 48,968 selectively antagonized the response to [beta Ala8]NKA(4-10) without affecting that to [Sar9]SP sulphone or septide in the ileum and colon. SR 48,968 produced noncompetitive antagonism of the response to the NK2 receptor agonist in the ileum and competitive antagonism in the colon. 7. MEN 10,376 and the cyclic pseudopeptide MEN 10,573 antagonized in a competitive manner the response to [beta Ala8]NKA(4-10) in the ileum and colon. While MEN 10,573 was equipotent in both preparations, MEN 10,376 was significantly more potent in the colon than in the ileum. MEN 10,376was also effective against septide in both preparations, without affecting the response to [Sar9] SP sulphone. MEN 10,573 antagonized the response to [Sar9]SP sulphone and septide in both preparations,pKB values against septide being intermediate, and significantly different from, those measured against[Beta Ala 8]NKA(4-10) and [Sa9]lSP sulphone.8. These findings show that tachykinin NK1 and NK2 receptors mediate contraction of the circular muscle of the guinea-pig ileum and colon. In both preparations NK1 receptor antagonists display higher apparent affinity when tested against septide than [Sar9]SP sulphone. These findings are compatible with the proposed existence of NK1 receptor subtypes in guinea-pig, although alternative explanations (e.g.agonist binding to different epitopes of the same receptor protein) cannot be excluded at present.Furthermore, an intraspecies heterogeneity of the NK2 receptor in the circular muscle of the guinea-pig ileum and colon is suggested.

Animals↗

PubMed1994

Tachykinin NK1 and NK2 receptor antagonists and atropine-resistant ascending excitatory reflex to the circular muscle of the guinea-pig ileum.

1. The aim of this study was to investigate the effect of various antagonists, selective for the tachykinin NK1 or NK2 receptor, on the atropine-resistant ascending excitatory reflex (AER) to the circular muscle of the guinea-pig ileum elicited by radial stretch (balloon distension) or electrical field stimulation. 2. Submaximal and maximal atropine- (1 microM) resistant AER elicited by balloon distension averaged about 40-50% and 70-90% of maximal circular spasm to 80 mM KCl, respectively. The NK1 receptor antagonist, (+/)-CP 96,345 (1 microM) inhibited both maximal and submaximal AER. FK 888 (1-3 microM) inhibited submaximal AER only. RP 67,580 (1 microM) was ineffective. The NK2 receptor antagonist, GR 94,800, inhibited both maximal and submaximal AER at all concentrations tested (0.1-3.0 microM), while SR 48,968 was effective only at 1.0 microM. The NK2 receptor antagonists, MEN 10,376 and MEN 10,573 inhibited both submaximal and maximal AER at 10 and 1.0 microM, respectively. 3. In other experiments, an NK1 receptor antagonist, (+/-)-CP 96,345 or FK 888 (1.0 microM in each case) was administered first and the effect of GR 94,800 (1.0 microM) on the residual AER response was determined; or GR 94,800 was administered first and the effect of (+/-)-CP 96,345 or FK 888 was determined. The results of these experiments indicated an additive effect produced by the combined treatment with NK1 and NK2 receptor antagonists. 4. Electrical field stimulation (10 Hz for 0.5 s, 10-20 V, 0.15-0.3 ms pulse width) with electrodes placed at 1.4-1.8 cm anal to the recording site, produced ascending contractions which were almost abolished by 10 MicroM hexamethonium (electrically-evoked AER). In the presence of apamin (0.1 MicroM) and N0-nitro-L-arginine (30 MicroM) these contractions were reproducible over 10 consecutive stimulation cycles.GR 94,800 (1 MicroM) and FK 888 (1 MicroM) both produced a partial inhibition of the electrically-evoked AER and their combined administration produced an inhibitory effect which was larger than that induced by each antagonist alone.5. FK 888 (1-3 MicroM), GR 94,800 (1-3 MicroM), MEN 10,573 (1 MicroM) and MEN 10,376 (10 MicroM) did not significantly affect the atropine-sensitive twitch contractions produced by electrical field stimulation of the guinea-pig ileum longitudinal muscle-myenteric plexus preparation, which were abolished by 10-30 MicroM procaine, 1 MicroM tetrodotoxin or 1 MicroM atropine. (+/-)-CP 96,345 (1 MicroM) and SR 48,968 (1 ILM)produced 12% and 27% inhibition of cholinergic twitches in the longitudinal muscle of the ileum,respectively.6. We conclude that both NK1 and NK2 receptors mediate the atropine-resistant AER to the circular muscle of the ileum. NK2 receptor activation plays a more important role than NK1 receptor activation in the AER evoked by radial stretch. Since a consistent fraction of the distension- and electrically evoked atropine-resistant AER persists in the presence of combined NK1 and NK2 receptor blockade,the existence of a third excitatory transmitter to the circular muscle of the ileum, in addition to acetylcholine and tachykinins, is suggested.

Animals↗

PubMed1994

Electrophysiological evidence for different release mechanism of ATP and NO as inhibitory NANC transmitters in guinea-pig colon.

1. The effect of the P2-purinoceptor antagonist, suramin, the specific N-type voltage-dependent calcium channel blocker, omega-conotoxin GVIA (omega-CgTx) and the delta-opioid receptor agonist [D-Pen2,D-Pen5] enkephalin (DPDPE) on the apamin-sensitive and apamin-resistant inhibitory junction potentials (i.j.ps) produced by electrical field stimulation (EFS) were investigated by means of a sucrose-gap technique in the circular muscle of the guinea-pig colon. 2. After incubation of muscle strips in either atropine (1 microM), guanethidine (3 microM) and NG-nitro-L-arginine (L-NOARG, 30 microM) or atropine, guanethidine and apamin (0.3 microM), the addition of the NK1 receptor antagonist, SR 140,333 (1 microM) abolished the non-adrenergic, non-cholinergic (NANC) excitatory junction potential (e.j.p.) and unmasked a pure apamin-sensitive i.j.p. (in the presence of L-NOARG) or a pure apamin-resistant i.j.p. (in the presence of apamin). Both types of i.j.p. were abolished by tetrodotoxin. 3. Suramin (30-300 microM) concentration-dependently inhibited the apamin-sensitive i.j.p., while the apamin-resistant i.j.p. was not significantly affected by suramin (up to 300 microM). L-NOARG (30 microM) markedly reduced the apamin-resistant i.j.p. 4. The delta-opioid receptor agonist, DPDPE (0.03-3 microM) concentration-dependently reduced the apamin-sensitive i.j.p., while leaving the apamin-resistant i.j.p. unaffected. Naloxone (1 microM) prevented the i.j.p. inhibition evoked by DPDPE (0.3 microM). 5. omega-CgTx (0.3 microM) markedly reduced the apamin-sensitive but not the apamin-resistant i.j.p. The application of DPDPE (3 MicroM), after development of a steady state inhibitory effect by omega-CgTx, evoked further inhibition of the apamin-sensitive ij.p., similar to the effect produced by DPDPE alone. The L-type calcium channel blocker, nifedipine (1 MicroM) did not significantly affect either the apamin-sensitive or the apamin-resistant ij.ps.6. These findings support the purinergic origin of the fast, apamin-sensitive ij.p. produced by EFS in the circular muscle of the guinea-pig colon and strongly suggest that the apamin-sensitive and the apamin-resistant components of the evoked ij.p. utilize different mechanisms for the secretion of theNANC transmitters, ATP and NO, respectively.

Action Potentials↗

PubMed1994

Evidence for a capsaicin-sensitive, tachykinin-mediated, component in the NANC contraction of the rat urinary bladder to nerve stimulation.

1. In the presence of atropine (1 microM) and guanethidine (3 microM), electrical field stimulation (EFS) of the rat isolated urinary bladder for 30 s induced a frequency-dependent (1-30 Hz) nonadrenergic non-cholinergic (NANC) triphasic contraction characterized by a peak response (within 10 s from onset of stimulation), a late response (determined as the tension developed at the end of the stimulation period) and a prolonged post-stimulus 'off' response. The latter peaked at 2-6 min from the end of the stimulation period. At 10 Hz, the amplitude of the three responses averaged 89 +/- 6, 76 +/- 6 and 18 +/- 3% of the response to 40 mM KCl, respectively. Tetrodotoxin (1 microM) abolished all contractile responses to EFS. 2. In capsaicin-pretreated bladder strips (10 microM for 15 min) the amplitude of the peak response to EFS (1-30 Hz for 30 s) was unchanged, the 'late' response to EFS was significantly reduced as compared to controls, and the post-stimulus response was absent, being replaced by a transient relaxation. 3. When varying train duration from 1 to 120 s at a frequency of 10 Hz, the differences between control and capsaicin-treated strips became evident for periods of stimulation > 10 s. 4. The tachykinin NK1 receptor antagonist, SR 140,333 (0.1-1 microM) had no effect on the peak response to EFS (10 Hz for 30 s) while it decreased significantly the late response at both concentrations tested (16 +/- 3 and 33 +/- 3% inhibition). At 1 micro M, SR 140,333 also significantly reduced (29 +/- 9% inhibition)the peak of the post-stimulus contraction. The tachykinin NK2 receptor antagonist, MEN 10,627(0. 1-1 9 MicroM) had no significant effect on the peak response to EFS (10 Hz for 30 s), and decreased the late response at 1 MicroM only (32 +/- 4% inhibition). MEN 10,627 inhibited the post-stimulus response at both concentrations tested and almost abolished it at 1 MicroM.5. The combined administration of SR 140,333 and MEN 10,627 (1 MicroM each) produced a small reduction(22 +/- 3% inhibition) of the peak response to EFS, a marked reduction (48 +/- 3% inhibition) of the late response and the abolition of the post-stimulus response which was replaced by a post-stimulus relaxation as observed in capsaicin-pretreated strips.6. SR 140,333 (0.1 and 1.0 MicroM) produced a large rightward shift in the concentration-response curve tothe NKI receptor agonist, [Sar9]substance P sulphone (apparent pKB 8.97 +/- 0.14), without affecting the response to the NK2 receptor-selective agonist, [Beta Ala8]neurokinin A (4-10). MEN 10,627 (0.1 and 1 MicroM)produced a large rightward shift of the concentration-response curve to [Beta Ala8]neurokinin A (4-10)(apparent pKB 8.95 +/- 0.16) without affecting the response to [Sarl substance P sulphone. SR 140,333 and MEN 10,627 (1.0 MicroM each) did not affect the contraction produced by exogenous ATP (1 mM).7. These findings provide evidence that the NANC contraction of the rat isolated urinary bladder to transmural nerve stimulation has two components, which are sharply differentiated by blockade of the efferent function of sensory nerves following in vitro capsaicin administration. The first component,probably mediated by endogenous ATP, is fully activated during short periods of nerve activity (< 10 s)and does not involve capsaicin-sensitive nerve afferents. The second component, which is capsaicin sensitive and tachykinin-mediated, is evident as a late 'on' response during nerve stimulation and as a post-stimulus 'off response for periods of stimulation >lOs. Activation of both NK1 and NK2receptors contributes to the capsaicin-sensitive responses.

Adenosine Triphosphate↗

PubMed1994

Facilitatory effects of selective agonists for tachykinin receptors on cholinergic neurotransmission: evidence for species differences.

1. Exogenous tachykinins modulate cholinergic neurotransmission in rabbit and guinea-pig airways. We have investigated the effect of selective tachykinin receptor agonists and antagonists on cholinergic neurotransmission evoked by electrical field stimulation (EFS) of bronchial rings in rabbit, guinea-pig and human airways in vitro to assess which type of tachykinin receptor is mediating this facilitatory effect. 2. Bronchial rings were set up for isometric tension recording. Contractile responses to EFS (60 V, 0.4 ms, 2 Hz for 10 s every min) and exogenous acetylcholine (ACh) were obtained and the effects of selective tachykinin agonists and antagonists were investigated. 3. In rabbit bronchi the endogenous tachykinins, substance P (SP) and neurokinin A (NKA) (10 nM) potentiated cholinergic responses to EFS (by 287.6 +/- 121%, P < 0.01 and 181.4 +/- 56.5%, P < 0.001 respectively). 4. The NK1 receptor selective agonist, [Sar9]SP sulphone (10 nM) evoked a maximal facilitatory action on cholinergic responses of 334.9 +/- 63% (P < 0.01) (pD2 = 8.5 +/- 0.06) an effect which was blocked by the selective NK1-receptor antagonist, CP 96,345 (100 nM) (P < 0.05) but not by the NK2 receptor antagonist, MEN 10,376 (100 nM). The NK2 receptor selective agonist, [beta Ala8]NKA(4-10) (10 nM), produced a maximum enhancement of 278 +/- 83.5% (P < 0.01) (pD2 = 8.7 +/- 0.1) an effect which was blocked by MEN 10,376 (100 nM) (P < 0.05) and not by CP 96,345. [MePhe7]NKB, an NK3 receptor selective agonist was without effect. 5. The rank order of potency of NK2 receptor antagonists against enhancement of cholinergic responses by [Beta Ala8]NKA(4-10) was MEN 10,376> L 659,877> R 396. This pattern together with the observation of the full agonist activity of MDL 28,564 indicates that the NK2 receptors in the rabbit bronchus are similar to those which are present in the rabbit pulmonary artery.6. Neither [Sar9]SP sulphone (5 nM) nor [Beta Ala8]NKA(4- 10) (1 nM) had any effect on contractile responses to ACh (10 MicroM) suggesting a pre-junctional mechanism of action.7. By contrast, in guinea-pig bronchi only the NK1-receptor agonist [Sar9]SP sulphone (3 nM) was effective in enhancing cholinergic neurotransmission but the effect was relatively small (maximal enhancement 25.7 +/- 5.5%, P<0.01). In human bronchial rings all the selective neurokinin agonists were without effect on cholinergic neurotransmission.8. These results suggest that tachykinins may play an important role in modulating cholinergic neurotransmission in rabbit (via NK1 and NK2 receptors) and guinea-pig airways (via NK1 receptor) but have no demonstrable effect on human airways

Adult↗

PubMed1994

Characterization of the tachykinin NK2 receptor in the human bronchus: influence of amastatin-sensitive metabolic pathways.

1. The aim of this study was to characterize the tachykinin NK2 receptor subtype mediating the spasmogenic response in the human isolated bronchus. The motor response to neurokinin A (NKA) and the selective NK2 agonist [beta Ala8]NKA(4-10), as well as the antagonistic effects of cyclic (L659,877) and linear (MEN 10376) peptide NK2 antagonists were assessed in the presence or absence of amastatin (an inhibitor of aminopeptidases A and M). 2. NKA was more potent than [beta Ala8]NKA(4-10) in eliciting bronchoconstriction (pD2 being 7,43 and 6,87 respectively). In the presence of amastatin (1 microM), the estimated affinity of [beta Ala8]NKA(4-10), but not that of NKA, was significantly increased to yield a pD2 of 7,44. 3. L659,877 and MEN 10376 inhibited [beta Ala8]NKA(4-10)-induced contraction with similar affinities; pA2 values were 5.7 +/- 0.22 and 6.3 +/- 0.32, respectively. Amastatin (1 microM) increased the potency of MEN 10376 to 7.28 +/- 0.46, whereas that of L659,877 was unaffected. 4. In the presence of amastatin the pseudopeptide MDL 28,564 behaved as a partial agonist. 5. We conclude that the NK2 receptor subtype present in the human bronchus has properties similar to those described for the circular muscle of the human colon and thus may be classified as a 'NK2A' subtype. We show that the apparent potency of peptides, bearing N-terminal acidic residues, is influenced by an amastatin-sensitive peptidase, possibly aminopeptidase A.

Amino Acid Sequence↗

PubMed1994

Effect of cromakalim and glibenclamide on spontaneous and evoked motility of the guinea-pig isolated renal pelvis and ureter.

1. We have investigated the effect of the potassium (K) channel opener, cromakalim, on the spontaneous myogenic activity of the guinea-pig isolated renal pelvis and on myogenic contractions evoked by direct electrical stimulation of the guinea-pig isolated ureter. 2. In the presence of Bay K 8644 (1 microM), electrical stimulation of the guinea-pig ureter (10 Hz for 1 s, pulse width 5 ms, 60 V) produced regular tetrodotoxin-(1 microM) resistant phasic contractions which were suppressed by 3 microM cromakalim. Glibenclamide (0.1-3 microM), 4-aminopyridine (4-AP, 0.1-2 mM) and tetraethylammonium (TEA, 1-10 mM) produced a concentration-dependent inhibition of the effect of cromakalim with the rank order of potency (EC50 in parentheses): glibenclamide (0.64 microM) >> 4-AP (1.11 mM) > TEA (6.6 mM). Apamin (0.1-0.3 microM) was without effect. 3. Cromakalim (0.1-10 microM) produced concentration-dependent inhibition and suppression of spontaneous contractions of the guinea-pig isolated renal pelvis and of evoked contractions of the ureter with EC50 values of 0.71 and 0.47 microM, respectively. 4. Glibenclamide (1 microM) produced a rightward shift of the concentration-response curve to cromakalim in both the renal pelvis and ureter, without producing depression of the maximal inhibitory effect. Glibenclamide did not affect the spontaneous activity of the renal pelvis while it produced a slight enhancement (10-15% increase) of evoked contractions of the ureter. Glibenclamide did not affect the inhibitory action of the adenylate cyclase activator, forskolin, in the renal pelvis or ureter. 5. In electrophysiological experiments (sucrose gap), cromakalim (0.3 and 1 microM) produced hyperpolarization of ureter smooth muscle. Cromakalim also produced a transient suppression of action potentials and accompanying phasic contractions evoked by electrical stimulation. Before suppression of evoked contractions, a shortening of action potential duration was observed concomitant with the developing hyperpolarization produced by cromakalim. A lower concentration (0.1 MicroM) of cromakalim did not affect membrane potential but shortened action potential duration and reduced the evoked contraction.6. Glibenclamide (1 MicroM) inhibited the hyperpolarizing action of cromakalim and prevented its inhibitory action on evoked action potentials and contractions of the ureter. Glibenclamide also produced a slight prolongation of action potential duration and increased the amplitude and duration of the accompanying mechanical response.7. These findings demonstrate that activation of cromakalim- and glibenclamide-sensitive K channels produces a powerful mechanism for regulation of pyeloureteral motility and suppression of latent pacemakers of the ureter in guinea-pig. Glibenclamide-sensitive K channels take part in determining action potential shape and duration in the guinea-pig ureter.

Action Potentials↗