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J R Grider

Publications and source records attributed to J R Grider.

At least 37 records · Page 2Linked to original sources
PubMed1998

5-HT4 receptor agonists and delta-opioid receptor antagonists act synergistically to stimulate colonic propulsion.

Opioid neurons exert a tonic restraint on inhibitory VIP/PACAP/NOS motoneurons of the enteric nervous system. A decrease in opioid peptide release during the descending phase of the peristaltic reflex, which underlies propulsive activity, leads to an increase in vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating polypeptide (PACAP), and nitric oxide (NO) release and circular muscle relaxation. These effects are accentuated by opioid receptor antagonists. Endogenous opioid peptides and selective opioid delta-, kappa- and mu-receptor agonists decreased the velocity of pellet propulsion in isolated segments of guinea pig colon, whereas selective antagonists increased velocity in a concentration-dependent fashion with an order of potency indicating preferential involvement of delta-receptors. 5-HT4 agonists (HTF-919 and R-093877), which also increase the velocity of propulsion, acted synergistically with the delta-receptor antagonist naltrindole; a threshold concentration of naltrindole (10 nM) shifted the concentration-response curve to HTF-919 to the left by 70-fold. A combination of 10 nM naltrindole with threshold concentrations of the 5-HT4 agonists caused significant increases in the velocity of propulsion (50 +/- 7 to 77 +/- 8%). We conclude that 5-HT4 agonists and opioid delta-receptor antagonists act synergistically to facilitate propulsive activity in isolated colonic segments.

Animals↗
PubMed1997

Characterization of PACAP receptors and signaling pathways in rabbit gastric muscle cells.

Pituitary adenylate cyclase-activating peptide (PACAP) receptors and their signaling pathways were characterized in dispersed rabbit gastric muscle cells. 125I-PACAP-27 and 125I-vasoactive intestinal peptide (VIP) binding to muscle cells were inhibited equally by PACAP and VIP (mean inhibitory concentration 0.8 to 1.3 nM) and desensitized to the same extent (70-80%) by exposure to either peptide. PACAP, like VIP, increased cytosolic free Ca2+ and the formation of L-[3H]citrulline, NO-3/NO-2, guanosine 3',5'-cyclic monophosphate (cGMP), and adenosine 3'5'-cyclic monophosphate (cAMP) and induced relaxation (mean effective concentration 1.8 +/- 0.1 nM) that was partly inhibited by NG-nitro-L-arginine (L-NNA), VIP-(10-28), and PACAP 6-38. L-[3H]citrulline and cGMP formation were blocked by nifedipine, L-NNA, and pertussis toxin (PTx), implying activation of a G protein-coupled, Ca(2+)-calmodulin-dependent nitric oxide (NO) synthase. PACAP-induced relaxation was inhibited to the same extent (46-49%) by nifedipine, L-NNA, PTx, and the protein kinase G inhibitor KT-5823; the inhibition reflected the component of relaxation mediated by the NO-cGMP pathway. The residual relaxation was abolished by the protein kinase A inhibitor H-89. The pattern of inhibition of all responses was identical to that observed with VIP. Desensitization with VIP or PACAP abolished cAMP formation but had no effect on L-[3H]citrulline and cGMP formation induced by either peptide. Receptor protection with VIP or PACAP preserved fully all responses (L-[3H]citrulline, cGMP, and cAMP formation and relaxation) to either peptide. The complete cross-competition, cross-desensitization, cross-antagonism, and cross-protection of receptors by either VIP or PACAP are consistent with interaction of both peptides with the same receptors; the receptors consist of two classes, each coupled to a distinct signaling pathway.

Adenylate Cyclase Toxin↗
PubMed1996

Distinct 5-HT receptors mediate the peristaltic reflex induced by mucosal stimuli in human and guinea pig intestine.

BACKGROUND & AIMS: The role of 5-hydroxytryptamine (5-HT) in regulating the peristaltic reflex in humans is unknown. The neural pathways subserving peristalsis induced by mucosal stimulation were characterized in human jejunum and guinea pig colon. METHODS: Compartmented flat-sheet preparations that enable measurement of 5-HT and sensory transmitter release into one compartment and mechanical responses in adjacent compartments were used. RESULTS: Mucosal stimuli (2-8 brush strokes) caused concomitant release of 5-HT and calcitonin gene-related peptide (CGRP) into the compartment where stimulation was applied in both species; in contrast, muscle stretch caused release of CGRP only. CGRP release as well as ascending contraction and descending relaxation of circular muscle induced by mucosal stimulation were inhibited by a selective 5-HT4 antagonist in human jejunum and by selective 5-HT4 and 5-HT3 antagonists in guinea pig colon. The effects of the 5-HT3 and 5-HT4 antagonists in guinea pig colon were additive. A selective 5-HT1P antagonist mimicked the effect of the 5-HT4 antagonist. The CGRP antagonist human CGRP8-37 inhibited ascending and descending responses in both species. CONCLUSIONS: 5-HT released by mucosal stimulation initiates a peristaltic reflex by activating 5-HT4/5-HT1P receptors on sensory CGRP neurons in human intestine and 5-HT4/5-HT1P and 5-HT3 receptors in guinea pig colon.

Animals↗
PubMed1996

5-HT released by mucosal stimuli initiates peristalsis by activating 5-HT4/5-HT1p receptors on sensory CGRP neurons.

The intestinal peristaltic reflex can be elicited by mucosal stimulation or circular muscle stretch. Muscle stretch activates extrinsic, whereas mucosal stimulation activates intrinsic calcitonin gene-related peptide (CGRP)-containing sensory neurons. The present study examined the role of 5-hydroxytryptamine (5-HT) in sensory transmission. A three-compartment preparation of rat colon was used that enables separate measurement of sensory transmitters and modulators. Mucosal stimuli (2-8 brush strokes) caused concurrent increase in 5-HT and CGRP release in proportion to the intensity of stimulation. Release of both 5-HT and CGRP occurred exclusively into the central compartment where the stimuli were applied. Exogenous 5-HT caused a concentration-dependent release of CGRP. Release of CGRP induced by exogenous 5-HT or mucosal stimulation was inhibited by selective 5-HT4 and 5-HT1p antagonists but was not affected by 5-HT1A, 5-HT2, and 5-HT3 antagonists. Ascending contraction and descending relaxation of circular muscle measured in the peripheral orad and caudad compartments, respectively, were also selectively inhibited by 5-HT4 and 5-HT1p antagonists added to the central but not peripheral compartments. In contrast, muscle stretch elicited CGRP but not 5-HT release; the ascending contraction and descending relaxation components of the peristaltic reflex induced by muscle stretch were not affected by 5-HT antagonists. We conclude that 5-HT released by mucosal stimulation initiates the peristaltic reflex by activating 5-HT4/5-HT1p receptors on sensory CGRP-containing neurons.

Animals↗
PubMed1996

Stoichiometry of neurally induced VIP release, NO formation, and relaxation in rabbit and rat gastric muscle.

Vasoactive intestinal peptide (VIP) release, nitric oxide (NO) formation, and relaxation induced by nerve stimulation were examined in rabbit and rat gastric muscle. VIP stimulated NO formation in muscle strips, whereas NO stimulated VIP release. Nerve stimulation (0.025-16 Hz or 2-940 pulses) elicited frequency-dependent stimulation of VIP release, NO formation, and relaxation, all significant at two to three pulses. NG-nitro-L-arginine (L-NMA) abolished NO formation, abolished VIP release and relaxation at low frequencies, and partly inhibited them at higher frequencies. Oxyhemoglobin (oxy-Hb) inhibited VIP release and relaxation by 80% at low frequencies and 20-30% at higher frequencies. VIP-(10-28) abolished NO formation and relaxation at lower frequencies and partly inhibited them at higher frequencies; in contrast, VIP-(10-28) augmented VIP release in both species. The pattern of inhibition was similar in both species. Inhibition of maximal NO formation by VIP-(10-28) (82% in rabbit; 48% in rat) implied that a major component of NO is formed in muscle cells by the action of VIP. Thus 1) inhibition of relaxation by L-NNA reflects suppression of NO and VIP release from nerve terminals and NO formation in muscle cells, 2) inhibition by VIP-(10-28) partly reflects suppression of NO formation in muscle cells, and 3) inhibition by oxy-Hb reflects neutralization of extracellular NO and suppression of VIP release. The study demonstrates the dual origin of NO from nerves and muscle and its interplay with VIP in regulating relaxation.

Animals↗
PubMed1996

Regulation of colonic propulsion by enteric excitatory and inhibitory neurotransmitters.

The contribution of excitatory and inhibitory motor neurotransmitters to colonic propulsion was examined in isolated segments of guinea pig colon. Synthetic fecal pellets were inserted at the proximal end of the segment, and the velocity of pellet propulsion across a fixed distance was measured in the presence and absence of selective neurotransmitter antagonists. The control velocity (0.97 +/- 0.02 mm/s) was inhibited in a concentration-dependent fashion by atropine and the neurokinin (NK)-2a antagonist MEN-10,376 [half-maximal inhibitory concentration (IC50), 1 microM; maximal inhibition, 98 +/- 1%]. The NK-1 antagonist GR-82,334 (10 microM) also inhibited velocity by 65 +/- 9%, consistent with involvement of acetylcholine, neurokinin A (NK-2 agonist), and substance P (NK-1 agonist) in the contractile components of the peristaltic reflex. Velocity was also inhibited in a concentration-dependent fashion by the nitric oxide synthase inhibitor NG-nitro-L-arginine (L-NNA; IC50, 1 microM; maximal inhibition, 96 +/- 2%) and by the vasoactive intestinal peptide (VIP) antagonist VIP-(10-28) (IC50, 30 nM; maximal inhibition, 64 +/- 6%), consistent with involvement of both nitric oxide and VIP in descending relaxation of circular muscle and contraction of longitudinal muscle. A combination of threshold concentrations of L-NNA and the NK-2a antagonist was synergistic (53 +/- 7% inhibition). The potentiation implied that the ascending and descending phases were functionally coupled in series. We conclude that blockade of neurotransmitters that mediate either phase of the peristaltic reflex inhibits colonic propulsive activity. Serial coupling of the phases leads to synergism between inhibitors, a condition of potential therapeutic importance.

Animals↗
PubMed1996

Inhibitory transmission in guinea pig stomach mediated by distinct receptors for pituitary adenylate cyclase-activating peptide.

Previous studies have shown that inhibitory transmission in guinea pig stomach involves an interplay between vasoactive intestinal peptide (VIP) and nitric oxide (NO). The present study examined the contribution of pituitary adenylate cyclase-activating peptide (PACAP), a homologous peptide present in gastric and intestinal myenteric neurons. VIP, PACAP-27 and PACAP-38 induced concentration-dependent relaxation that was partly inhibited by the antagonists VIP10-28 and PACAP6-38 and the NO synthase inhibitor NG-nitro-L-arginine (L-NNA). Only relaxation induced by PACAP-27 and PACAP-38 was partly inhibited by apamin. Electrical field stimulation (0.25-16 Hz) induced frequency-dependent relaxation and PACAP release (maximum of 35.7 fmol/100 mg-min or 7-fold above basal levels). Electrical field stimulation-induced relaxation was partly inhibited by a combination of selective monoclonal antibodies to PACAP-27 and PACAP-38 (42 +/- 7% at 16 Hz) and by the antagonists VIP10-28 (29 +/- 9%) and PACAP6-38 (29 +/- 3%). The relaxation was also partly inhibited by L-NNA (51 +/- 12% at 16 Hz) and apamin (36 +/- 4%). The effects of a combination of apamin and L-NNA were additive, amounting to 75 +/- 3% inhibition. The effect of L-NNA reflected inhibition of NO release from nerve terminals, as well as NO generation in muscle cells by the action of VIP and PACAP; the effect of apamin reflected blockade of the action of PACAP. Thus, inhibitory transmission in guinea pig gastric fundus represents the combined actions of VIP, PACAP and NO released from nerve terminals and NO generated in muscle cells. The postjunctional actions of PACAP are mediated by a VIP/PACAP-II receptor and by a PACAP-specific, apamin-sensitive receptor.

Animals↗
PubMed1995

Coexpression of 5-HT2A and 5-HT4 receptors coupled to distinct signaling pathways in human intestinal muscle cells.

BACKGROUND & AIMS: The type and function of 5-hydroxytryptamine (5HT) receptors on intestinal muscle cells in humans are not known. 5-HT receptors were characterized pharmacologically and by radioligand binding. METHODS: Contraction, relaxation, inositol 1,4,5-triphosphate (IP3) and adenosine 3',5'-cyclic monophosphate (cAMP) formation, and 5-HT binding were measured in dispersed muscle cells and in cells in which only one receptor type was preserved by selective receptor protection. RESULTS: 5-HT binding was completely inhibited by 5-HT and partially by 5-HT2A (ketanserin), 5-HT4 (SDZ-205,557), and 5-HT1p (N-acetyl-5-hydroxytryptophyl-5-hydroxytryptophan amide; 5-HTP-DP) receptor antagonists. 5-HT caused contraction that was inhibited by ketanserin and augmented by SDZ-205,557 and 5-HTP-DP. In the presence of ketanserin, 5-HT caused relaxation of cholecystokinin-contracted cells that was inhibited by SDZ-205,557 and 5-HTP-DP. 5-HT increased IP3, which was inhibited by ketanserin, and cAMP, which was inhibited by SDZ-205,557 and 5-HTP-DP. In cells with only 5-HT2A receptors, 5-HT caused contraction only, and residual binding was inhibited by ketanserin. In cells with only 5-HT4/5-HT1p receptors, 5-HT caused only relaxation and residual binding was inhibited by SDZ-205,557 and 5-HTP-DP. CONCLUSIONS: 5-HT2A receptors mediating contraction and 5-HT4 receptors mediating relaxation coexist on human intestinal muscle cells. The 5-HT4 receptors are closely similar or identical to 5-HT1p receptors.

4-Aminobenzoic Acid↗
PubMed1995

Adenosine A1 and A2b receptors coupled to distinct interactive signaling pathways in intestinal muscle cells.

Adenosine receptors and the signaling pathways to which they are coupled were examined in dispersed intestinal muscle cells. The receptors were characterized by their ability to induce contraction or relaxation, mobilize Ca2+ and stimulate or inhibit cAMP, in naive cells and in cells where only one receptor type was preserved by selective receptor protection. Adenosine elicited contraction and increased [Ca2+]i and cAMP; the contraction was mimicked by the A1 selective agonist, cyclopentyladenosine. A selective A1 antagonist, 8-cyclopentyl-1,3-dipropylxanthine, and pertussis toxin abolished contraction and the increase in [Ca2+]i and augmented the increase in cAMP. Conversely, a preferential A2 antagonist, 9-chloro-2-(2-furyl) [1,2,4]triazolo[1,5-c]quinazolin-5-amine augmented contraction and the increase in [Ca2+]i and abolished the increase in cAMP; a cAMP-kinase inhibitor, Rp-cAMP[S], had a similar effect, augmenting contraction and the increase in [Ca2+]i. Adenosine elicited also relaxation of maximally contracted cells that increased or decreased in parallel with cAMP. The selective A2a agonist, 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamido adenosine, was a very weak relaxant agent, and the selective A2a antagonist, 8-(3-chlorostyryl)caffeine, had no effect on adenosine-induced relaxation. In cells where only A1 receptors were preserved, the cAMP response to adenosine was abolished, although contraction and [Ca2+]i were increased to the same extent as when naive cells were treated with the A2 antagonist. Conversely, in cells where only A2 receptors were preserved, contraction and the increase in [Ca2+]i were abolished and the increase in cAMP was augmented to the same level as when naive cells were treated with the A1 antagonist.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1994

Regulation of the descending relaxation phase of intestinal peristalsis by PACAP.

The presence of pituitary adenylate cyclase-activating peptide (PACAP), a homologue of vasoactive intestinal peptide (VIP), in enteric neurons suggests that it may involved in the regulation of the descending relaxation phase of the peristaltic reflex. The role of PACAP was evaluated by measurement of PACAP release and by immuno-neutralization with specific monoclonal antibodies to PACAP-27 and PACAP-38, and an antibody to VIP. Electrical field stimulation at 4 Hz caused a 12-fold increase in PACAP release that was inhibited by 53 +/- 6% (P < 0.01) by the nitric oxide synthase inhibitor, NG-nitro-L-arginine (L-NNA). Orad stretch of colonic segments elicited descending relaxation and PACAP release in proportion to the degree of stretch. PACAP release induced by 10-g stretch was inhibited by 67 +/- 10% (P < 0.01) by L-NNA. Previous studies (Am. J. Physiol., 264 (1993) G334-G340) showed that orad stretch elicits also VIP release and nitric oxide (NO) production and that VIP release is inhibited (59%) by L-NNA. Preincubation of the segments with PACAP-27 plus PACAP-38 antibodies (50 micrograms/ml each), or with VIP antibody (1:60) inhibited descending relaxation at all degrees of stretch (inhibition with PACAP antibodies: 90 +/- 8% with 2-g and 22 +/- 5% with 10-g stretch). Preincubation with both PACAP and VIP antibodies virtually abolished descending relaxation. A similar pattern was observed with the antagonists, PACAP6-38 and VIP10-28, alone and in combination.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Role of cholecystokinin in the regulation of gastrointestinal motility.

Cholecystokinin, a hormone released from endocrine cells of the upper small intestine in response to amino acids and fatty acids in chyme, has potent effects on gut smooth muscle contractility. Depending on the region of the gut, the effect of cholecystokinin may be neurally mediated, direct, or both. Neurally-mediated effects may be relaxant or contractile depending on the transmitter released by cholecystokinin. Based on mimicry by infusion of cholecystokinin to postprandial levels and the ability of specific cholecystokinin receptor antagonists to abolish effects of endogenous cholecystokinin released in response to a meal, three physiological effects of cholecystokinin, all of which are neurally-mediated, have been identified: contraction of the gallbladder mediated by cholecystokinin-induced release of acetylcholine, relaxation of the sphincter of Oddi mediated by cholecystokinin-induced release of vasoactive intestinal peptide and inhibition of gastric emptying mediated by cholecystokinin-induced activation of an inhibitory vago-vagal reflex involving vasoactive intestinal peptide-induced relaxation of the gastric fundus. Gallbladder contraction and relaxation of the sphincter of Oddi regulate the flow of bile, and inhibition of gastric emptying regulates the flow of chyme into the duodenum. Combined with the potent stimulation of pancreatic enzyme secretion by cholecystokinin, these effects insure optimal conditions for digestion and absorption of nutrients by the intestine.

Animals↗
PubMed1994

CGRP as a transmitter in the sensory pathway mediating peristaltic reflex.

The presence of calcitonin gene-related peptide (CGRP) in enteric and dorsal root ganglion neurons suggests that it might be involved as a transmitter in the sensory pathway that mediates the peristaltic reflex. This notion was examined in a three-compartment flat-sheet colonic preparation in which stimuli (muscle stretch or mucosal stimulation) were applied to the central compartment, while ascending contraction and descending relaxation were measured in the peripheral compartments. Both muscle stretch and mucosal stroking applied to the central compartment elicited CGRP release into the central, but not peripheral, compartments. The magnitude of release was proportional to the intensity of stimulation. Addition of the CGRP antagonists, human CGRP-(8-37) and [Tyr0]CGRP-(28-37), to the central compartment inhibited descending and ascending responses elicited by muscle stretch or mucosal stimulation. Addition of the sensory neurotoxin, capsaicin (0.01 to 1 microM), to the central compartment caused concentration-dependent release of CGRP; the resultant depletion of sensory transmitter resulted in a concentration-dependent decrease in ascending and descending responses elicited by muscle stretch and mucosal stimulation. Extrinsic denervation decreased basal CGRP release and abolished CGRP release and peristaltic responses normally elicited by muscle stretch but not CGRP release or peristaltic responses elicited by mucosal stimulation. The results indicate that extrinsic sensory pathways, which mediate the peristaltic response to muscle stretch, and intrinsic sensory pathways, which mediate the peristaltic response to mucosal stimulation, utilize CGRP as a sensory transmitter.

Animals↗
PubMed1994

Differential expression of substance P, somatostatin, and VIP in neurons from cultured myenteric ganglia.

The expression of three enteric neuropeptides was examined in freshly dispersed ganglia and in ganglia cultured for up to 28 days. During culture, glial cells grew into a flat sheet surrounding a cluster of neurons identified with neuron-specific enolase (13 +/- 2/ganglion), which remained constant throughout the period of culture. The neurons underwent a distinctive temporal change, resulting in overexpression of substance P (SP), normal expression of somatostatin, and virtual suppression of vasoactive intestinal peptide (VIP). Three weeks after the start of culture, the ganglia contained and released (in response to 55 nM KCl, 0.1 mM 1,1-dimethyl-4-phenylpiperazinium, or 1 microM gastrin-releasing peptide) twice as much SP as freshly dispersed ganglia, corresponding to a sevenfold increase per cultured neuron; content and release of somatostatin did not change. SP content and release declined to 1.5% of those found in control cultures when nonneuronal cells were suppressed with cytosine arabinoside but were partially restored (13-17% of control) by nerve growth factor. In marked contrast, VIP was minimally (< 1%) present in and released from ganglia after the third day in culture. Suppression of VIP could reflect a selective loss of VIP neurons and/or VIP expression.

Animals↗
PubMed1994

Interplay of somatostatin, opioid, and GABA neurons in the regulation of the peristaltic reflex.

The interplay of somatostatin, gamma-aminobutyric acid (GABA), and opioid neurons in the regulation of the descending relaxation phase of peristalsis was examined in isolated rat colonic segments. Release of somatostatin, GABA, vasoactive intestinal peptide (VIP), and L-[3H]citrulline [coproduct and index of nitric oxide (NO) production] increased, and release of Met-enkephalin decreased, during descending relaxation. Somatostatin antiserum (1:50) inhibited GABA and L-[3H]citrulline and reversed Met-enkephalin from decrease below to increase above basal level; exogenous somatostatin had the opposite effect. Bicuculline (GABAA antagonist) inhibited L-[3H]citrulline, had no effect on somatostatin, and reversed Met-enkephalin from decrease below to increase above basal level; exogenous GABA had the opposite effect. Naloxone increased GABA and L-[3H]citrulline but had no effect on somatostatin; exogenous Met-enkephalin had the opposite effect. In all instances the changes in L-[3H]citrulline paralleled those previously obtained with VIP. The results are consistent with the operation of a circuit in which somatostatin neurons inhibit the activity of opioid neurons, causing a decrease in Met-enkephalin. The decrease in Met-enkephalin initiated by somatostatin is accentuated by a reciprocal inhibitory pathway linking GABA and opioid neurons. The decrease in Met-enkephalin eliminates the inhibitory influence of opioid neurons on VIP/NO neurons and leads to increase in VIP, NO, and descending relaxation.

Animals↗
PubMed1994

Distinct populations of sensory neurons mediate the peristaltic reflex elicited by muscle stretch and mucosal stimulation.

Recent studies suggest that muscle stretch and mucosal stimulation elicit intestinal peristalsis by activating distinct populations of sensory neurons that converge on the same population of enteric motor neurons. The present study sought to characterize the origin and projections of these sensory neurons. The reflex was elicited by applying muscle stretch and mucosal stroking to the central compartment of a three-compartment flat-sheet preparation of rat colon while ascending contraction and descending relaxation were measured in the orad and caudad compartments, respectively. Identical graded responses were elicited by muscle stretch and mucosal stimulation: atropine (1 microM) and the tachykinin antagonist spantide (10 microM) inhibited ascending contraction when added to the orad compartment only, while the vasoactive intestinal peptide antagonist VIP10-28 (10 microM) and the NO synthase inhibitor NG-nitro-L-arginine (100 microM) inhibited descending relaxation when added to the caudad compartment only. Addition of capsaicin (1 microM) to the central compartment for 30 min abolished ascending contraction and descending relaxation elicited by muscle stretch and mucosal stimulation. Recovery of response was complete when capsaicin was applied to the mucosa of the colon in situ and measurements made 1 d after, implying that at this low concentration capsaicin depleted sensory nerve terminals of their transmitter content.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Coexistence of three tachykinin receptors coupled to Ca++ signaling pathways in intestinal muscle cells.

Receptors for tachykinins and the signaling pathway to which they are coupled were characterized in dispersed muscle cells from the longitudinal muscle layer of the rat intestine. A technique of receptor protection whereby selective agonists and antagonists were used to protect one receptor while other receptors were inactivated with N-ethylmaleimide enabled each tachykinin receptor type to be identified separately. Protection of neurokinin (NK)-1 receptors with the selective NK-1 agonist, substance P methylester, or antagonist, GR-82,334 (Glp-Ala-Asp-Pro-Asn-Lys-Phe-Tyr-D-Pro[spiro-gamma-lactam]Leu-Trp-NH2), preserved the contractile response and increase in cytosolic-free Ca++ ([Ca++]i) induced by substance P methylester only; protection of NK-2 receptors with the selective NK-2 agonist, beta-[Ala8]NKA(4-10), or the selective NK-2b antagonist, L-659,877 [cyclo(Leu-Met-Gln-Trp-Phe-Gly)], preserved the contractile response and increase in [Ca++]i induced by beta-[Ala8]NKA(4-10) only; and protection of NK-3 receptors with the selective NK-3 agonist, senktide succinyl-[Asp6,MePhe8]substance P(6-11), preserved the contractile response and increase in [Ca++]i induced by succinyl-[Asp6,MePhe8]substance P(6-11) only. When used as a protective agent, the NK-2a antagonist, MEN-10,376 (H-Asp-Tyr-D-Trp-Val-D-Trp-D-Trp-Lys-NH2), did not preserve the response to any tachykinin agonist. Protection of NK-1, NK-2 and NK-3 receptors preserved fully the responses to the preferential endogenous agonists, substance P, NKA and NKB, respectively, but they also preserved in part (30-40%) the responses to the nonpreferential agonists. Because substance P and NKA are coreleased from the same precursor in intestinal muscle tissue, the pattern implied the existence of considerable spareness in the contractile response of muscle cells to tachykinins. Studies on dispersed circular muscle cells using selective tachykinin agonists as protective agents confirmed the presence of three tachykinin receptor types. The results demonstrate the coexistence of NK-1, NK-2b and NK-3 receptors on muscle cells of rat intestine that are preferentially activated by substance P, NKA and NKB, respectively, and are coupled separately to one signaling pathway mediating contraction.

Amino Acid Sequence↗
PubMed1994

Inhibitory transmission in tenia coli mediated by distinct vasoactive intestinal peptide and apamin-sensitive pituitary adenylate cyclase activating peptide receptors.

Inhibitory transmission in tenia coli involves both vasoactive intestinal peptide (VIP) and an apamin-sensitive transmitter. The present study examined whether pituitary adenylate cyclase activating peptide (PACAP) is released from tenia coli and accounts for the apamin-sensitive component of neurally mediated relaxation. Electrical field stimulation (0.25-4 Hz) elicited frequency-dependent relaxation and PACAP release; earlier studies had shown a similar pattern for VIP release and an absence of nitric oxide generation in this tissue. A combination of specific PACAP-27 and PACAP-38 monoclonal antibodies (each 100 micrograms/ml), the PACAP antagonist PACAP6-38 and desensitization with PACAP inhibited relaxation induced by all frequencies of stimulation. The magnitude of inhibition elicited by each treatment (38 +/- 3%-41 +/- 3% at 4 Hz) was similar to that elicited by apamin (44 +/- 11%) and was not augmented by apamin. VIP antibody (1:60), the VIP antagonist, VIP10-28 and VIP desensitization also inhibited relaxation (33 +/- 2%-35 +/- 5% at 4 Hz). Inhibition by each treatment was augmented additively by apamin (76 +/- 3%-85 +/- 3%) as well as by combination with PACAP antibody, PACAP antagonist and PACAP desensitization (76 +/- 6%-80 +/- 3%). Measurements in muscle strips and dispersed tenia coil muscle cells showed that VIP10-28 inhibited relaxation induced by VIP only, and PACAP6-38 inhibited relaxation mediated by PACAP-27 or PACAP-38 only, implying interaction of VIP and PACAP with distinct receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗