Biomedical subjects

G E Knight

Publications and source records attributed to G E Knight.

At least 19 recordsLinked to original sources

PubMed2002

P2 receptors in the murine gastrointestinal tract.

The actions of adenosine, adenosine 5'-triphosphate (ATP), 2-methylthio adenosine diphosphate ADP (2-MeSADP), 2-methylthio ATP (2-MeSATP), alpha,beta-methylene ATP (alpha,beta-meATP) and uridine triphosphate (UTP) on isolated segments of mouse stomach (fundus), duodenum, ileum and colon were investigated. The localization of P2Y(1), P2Y(2), P2Y(4), P2X(1) and P2X(2) receptors and neuronal nitric oxide synthase (NOS) were examined immunohistochemically, and P2Y(1) mRNA was examined with in situ hybridization. The order of potency for relaxation of longitudinal muscle of all regions was: 2-MeSADP>/=2-MeSATP>alpha,beta-meATP>ATP=UTP=adenosine. This is suggestive of P2Y(1)-mediated relaxation and perhaps a further P2Y receptor subtype sensitive to alpha,beta-meATP. As ATP and UTP are equipotent, the presence of a P2Y(2) receptor is indicated. ATP responses were inhibited by the P2Y(1)-selective antagonist MRS 2179, and suramin. P2Y(1) receptors were visualized immunohistochemically in the smooth muscle of the ileum and in a subpopulation for myenteric neurones, which also stained for NOS. P2Y(1) mRNA was localized in neurones in both myenteric and submucosal ganglia in the ileum. Taken together, these results suggest that ATP was acting on non-adrenergic, non-cholinergic inhibitory neurons, which release both nitric oxide (NO) and ATP. Reduced relaxations to 2-MeSADP by tetrodotoxin and N(omega)-nitro-L-arginine methyl ester, are consistent with this possibility. Adenosine acts via P1 receptors to relax smooth muscle of the mouse gut. Segments of mouse colon (in contrast to the stomach and small intestine) were contracted by nucleotides with the potency order: 2-MeSATP>alpha,betameATP>ATP; the contractions showed no desensitization and were antagonized by suramin and PPADS, consistent with responses mediated by P2X(2) receptors. Immunoreactivity to P2X(2) receptors was demonstrated on both longitudinal and circular muscle of the colon, but not in the other regions of the gut, except for a small subpopulation of myenteric neurones. In summary, neuronal P2Y(1) receptors appear to mediate relaxation, largely through NO in all regions of the mouse gut, and to a lesser extent by P2Y(1), P2Y(2) and a novel P2Y receptor subtype responsive to alpha,beta-meATP in smooth muscle, while P2X(2) receptors mediate contraction of colonic smooth muscle.

Animals↗

PubMed2002

ATP is released from guinea pig ureter epithelium on distension.

Distension of the perfused guinea pig ureter at pressures from 20 to 700 cmH(2)O increased the amount of ATP released from the epithelium in a pressure-dependent manner. During basal perfusion (40 microl/min), the perfusate contained 10 pmol/ml ATP; this increased 10- to 50-fold at various distending pressures. ATP was released from epithelial cells during distension as mechanical removal of the urothelium blocked release. No lactate dehydrogenase was detected in the perfusate, and scanning electron microscopy confirmed an intact urothelium after distension. ATP was not released due to the activation of stretch-activated channels, as gadolinium (10 microM) failed to affect ATP release. Glibenclamide (10 microM), known to inhibit two members of the ATP-binding cassette (ABC) protein family, did not affect ATP release after distension; nor did verapamil (10 microM). In contrast, both monensin (100 microM) and brefeldin A (10 microM), which interfere with vesicular formation or trafficking, inhibited distension-evoked ATP release, which was Ca(2+)-dependent. This suggests that ATP release from the ureter epithelium might be mediated by vesicular exocytosis. The role of ATP released by distension of hollow visceral organs is discussed in relation to the concept of purinergic mechanosensory transductions, with special reference to nociception and the activation of P2X(3) receptors on the subepithelial sensory nerves.

Adenosine Triphosphate↗

PubMed2001

Identification of P1 and P2 purinoceptors in the aorta of the lizard (Agama sp.).

In the isolated Agama lizard aorta, acetylcholine (ACh; 3 nM-100 microM), noradrenaline (NA; 30 nM-0.3 mM), adrenaline (Adr; 30 nM-300 microM), adenosine 5'-triphosphate (ATP; 30 nM-1 mM), alpha,beta-methylene ATP (alpha,beta-meATP; 10 nM-10 microM), beta,gamma-methylene ATP (beta,gamma-meATP; 0.1-300 microM), 2-methylthio ATP (2-meSATP; 30 nM-30 microM) and high concentrations of uridine triphosphate (UTP; 1 microM-1 mM), all produced constriction. The P2 receptor antagonists pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS; 30 microM), suramin (0.1 mM) and Reactive blue 2 (30 microM) all raised vascular tone and could not be utilized and the antagonist 2'-O-(trinitrophenyl) ATP (TNP-ATP; 0.1 microM) had no effect on responses to the ATP analogues. alpha,beta-MeATP (3 microMx3) desensitised responses to alpha,beta-meATP (10 microM) and beta,gamma-meATP (0.3 mM), but not to ATP (0.3 mM) or 2-meSATP (30 microM). On pre-constricted aorta (EC50 concentration of either ACh or Adr), adenosine (1 microM-1 mM), the A1-selective agonist N6-cyclopentyl adenosine (CPA; 1-300 microM) [but not the A2- and A3-selective agonists CGS 21680 and IB-MECA respectively (both up to 30 microM)] and sodium nitroprusside (10 nM-100 microM) produced vasodilatation. Adenosine vasodilatation was antagonised by 8-p-sulfophenyl-theophylline (8-pSPT; 30 microM) but not by N(omega)-nitro-L-arginine methyl ester (L-NAME; 0.1 mM). ATP (up to 0.3 mM), 2-meSATP (up to 10 microM) and UTP (up to 1 mM) were not vasodilators. In summary, A1 receptors mediating relaxation and excitatory P2X1 receptors were identified in the smooth muscle of the lizard aorta. However, in contrast to mammalian aorta, P2Y receptors on endothelial cells mediating vasodilatation via nitric oxide do not appear to be present.

Adenosine↗

PubMed2000

The effects of cyclophosphamide on neurotransmission in the urinary bladder of Suncus murinus, the house musk shrew.

This study has shown that cyclophosphamide treatment of the insectivore Suncus murinus, causes a down regulation in both muscarinic and P2X receptors, together with a reduced responsiveness to exogenous histamine (0.3 mM) in the urinary bladder. Electrical field stimulation (70 V, 0.3 ms, 0.5-16 Hz, 10 s every 5 min) of bladders from both control and cyclophosphamide-treated animals showed identical responses. Since post-junctional alterations have been revealed by the reduced responsiveness to exogenous carbachol (0.1 microM-3 mM) and beta,gamma-methylene ATP (0.3-300 microM), it would appear that in the bladders of cyclophosphamide-treated animals there is also a pre-junctional effect, increased transmitter release compensating for the down regulation of the receptors. As the pattern of neurotransmission of the bladder of suncus more closely resembles that of human detrusor than other commonly studied laboratory animals, this insectivore appears to be a useful animal model for the study of bladder neurotransmission in pathophysiological conditions.

Adenosine Triphosphate↗

PubMed2000

Increased connexin43 gap junction protein in hamster cardiomyocytes during cold acclimatization and hibernation.

OBJECTIVE: The physiology of hibernation is characterized by dramatic reductions of heart rate, respiration, metabolism, blood pressure and body temperature and by resistance to ventricular fibrillation. Gap junctions in the heart provide low resistance pathways, facilitating electrical and metabolic coupling between cardiac muscle cells for coordinated action of the heart and tissue homeostasis. The conductance of these junctions, and therefore their function, is likely to be affected by the physiological changes that take place during hibernation. Our objective was to quantitate gap junction protein levels in cold acclimatization, hibernation and arousal. METHODS: We have used specific antibodies to connexins 43 and 40, in combination with confocal microscopy, to quantitatively analyze the expression of connexin protein in hamster (Mesocricetus auratus) left ventricles in four animal groups: normal controls at euthermy, cold controls (cold-exposed animals that did not undergo hibernation), hibernating animals and animals aroused from hibernation for 2 h. RESULTS: Connexin40 immunostaining was not detected in ventricular cardiomyocytes in any animal group but connexin43 was found in all groups. Connexin43 expression was significantly enhanced in hibernation and cold control ventricular cardiomyocytes. Total plaque area, numerical density and plaque size were higher in the cold controls and hibernating hamsters compared to normal controls and animals aroused from hibernation. CONCLUSION: It is possible that the increased size and number of connexin43 gap junction plaques in the cold controls may represent a compensatory response in order to maintain sufficient gap junction communication during physiological conditions that would reduce conductance. These changes may represent a mechanism by which the hamster avoids ventricular fibrillation during hibernation and arousal.

Adaptation, Physiological↗

PubMed1999

NANC relaxation of the circular smooth muscle of the oesophagus of the Agama lizard involves the L-arginine-nitric oxide synthase pathway.

On carbachol (CCh; 10-30 microM) pre-contracted circular muscle strips of the Agama lizard oesophagus, electrical field stimulation evoked frequency-dependent relaxations in the presence of guanethidine (1 microM) and indomethacin (1 microM). These non-adrenergic inhibitory responses were concentration-dependently inhibited by the nitric oxide synthase (NOS) inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) within a concentration range of 30-300 microM but not D-NAME (up to 300 microM), although a component remained at 4-16 Hz even with 300 microM L-NAME. The inhibition by L-NAME (300 microM) was completely prevented when L-arginine (L-Arg; 15 mM) but not D-Arg (up to 15 mM) was applied simultaneously with L-NAME (300 microM). Increasing the L-NAME concentration to 1 mM had no additional inhibitory effect. Sodium nitroprusside (SNP) concentration-dependently relaxed pre-contracted oesophageal strips, L-NAME (up to 300 microM) had no effect. Neither adenosine 5'-triphosphate (up to 0.1 mM) nor vasoactive intestinal polypeptide (up to 0.1 microM) caused the pre-contracted oesophagus to relax. This study has shown that the NANC inhibitory response of the Agama lizard oesophagus circular muscle largely involves the L-Arg-NOS pathway as seen by the effect of L-NAME, L-Arg and SNP. The identity of the L-NAME-resistant component(s) and the lack of effect of tetrodotoxin (up to 3 microM) and omega-conotoxin GVIA (up to 0.1 microM) in relation to the nature of the inhibitory response are discussed.

Adrenergic Agents↗

PubMed1998

Effect of hibernation on responses of hamster vas deferens to sympathetic nerve stimulation and exogenous neurotransmitters.

The present study investigated the responses of the vas deferens to sympathetic nerve stimulation and exogenous neurotransmitters taken from golden hamsters which had undergone 8 weeks of hibernation, 2 h of arousal from hibernation, those exposed to the cold but which failed to hibernate and age-matched control animals. Electrical field stimulation (EFS) of the vas deferens from each group produced frequency-dependent, tetrodotoxin-sensitive contractions. Contractions elicited by low frequencies of EFS in the hibernating group were significantly greater than in the other groups in the absence of any blocking agents. In the presence of the alpha1-adrenoceptor antagonist prazosin (3 microM) responses from all groups were reduced by approximately 40%, with the residual responses from the hibernating group being somewhat increased compared to the other groups. In the presence of the P2X receptor antagonist pyridoxalphosphate-6-azophenyl-2'4'-disulphonic acid (30 microM), there was no significant difference in responses from all 4 groups. Exogenously applied beta, gamma-methylene ATP (beta,gamma-meATP; 0.1-300 microM), a P2X receptor agonist, and noradrenaline (NA; 30 nM(-1) mM) both caused transient concentration-dependent contractions in all groups of animals. Contractions to beta,gamma-meATP at concentrations above 0.3 microM, and NA above 0.3 microM in the hibernating animals were statistically significantly greater than the cold- and age-matched control groups, although not significantly different from the aroused group. This study has shown postjunctional increases in responses to beta,gamma-meATP and NA as a result of hibernation, possible explanations for these increases are discussed.

Adenosine Triphosphate↗

PubMed1998

Neurogenic and non-neurogenic responses in the urinary bladder of hibernating hamster.

1. Purinergic and cholinergic components of parasympathetic neurotransmission and contractile responses to exogenous alpha,beta-methylene ATP, acetylcholine, substance K, substance P, calcitonin gene-related peptide, vasoactive intestinal polypeptide and capsaicin have been investigated in the urinary bladder of hibernating hamsters (4 weeks), cold exposed (4 weeks) and age-matched controls. 2. Electrical field stimulation (EFS) evoked increased frequency-dependent contractions in the detrusor strips from hibernating hamsters compared with those obtained from cold-exposed and age-matched animals. Tetrodotoxin (10(-6) M) completely blocked the frequency-dependent contractions in all groups. 3. The purinergic component of the parasympathetic neurotransmission was not affected in hibernating and cold-exposed animals while the cholinergic component was increased with respect to age-matched animals. The neurogenic response to EFS, still present after incubation with atropine (10(-6) M) and suramin (10(-4) M), was attenuated by indomethacin (10(-6) M) and blocked by tetrodotoxin (10(-6) M). 4. Exogenous administration of alpha,beta-methylene ATP elicited a significantly reduced contraction in strips from hibernating and cold-exposed hamsters relative to age-matched animals. The contractile response to exogenous acetylcholine was greater in the detrusors from hibernating hamsters than in cold-exposed and age-matched animals. Substance K elicited reduced contractions in preparations from hibernating animals compared with cold-exposed and control animals. Calcitonin gene-related peptide, vasoactive intestinal polypeptide, substance P and capsaicin did not elicit any relaxant or contractile response either at resting tone or in carbachol (5 x 10(-7) M)-precontracted tissues. 5. In summary, our findings indicate that 4 weeks of hibernation can significantly increase neurogenic responses in the hamster urinary bladder. This appears to be due to an increase in postjunctional responses to acetylcholine. In contrast, there was a decrease of the postjunctional responses to the parasympathetic cotransmitter ATP and also to the sensory-motor neurotransmitter substance K.

Acetylcholine↗

PubMed1996

The effects of purine compounds on the isolated aorta of the frog Rana temporaria.

1. In the isolated aorta of the frog, Rana temporaria, adenosine concentration-dependently, endothelium-independently relaxed adrenaline pre-constricted vessels. None of the adenosine analogues including D-5'-(N-ethylcarboxamide) adenosine (NECA), R- and S-N6-(2-phenylisopropyl) adenosine (R-and S-PIA) and 2-chloroadenosine (2-CA), or the more selective A1, A2 and A3 agonists cyclopentyladenosine (CPA), CGS 21680 and N6-(3-iodobenzyl) adenosine-5'-N-methylcarboxamide (IB-MECA) respectively, had any effect. 2. The non-selective adenosine antagonist, 8-p-sulphophenyl-theophylline (8-pSPT; 30 microM) failed to inhibit adenosine relaxations, as did NG-nitro-L-arginine methyl ester (L-NAME; 0.1 mM) and indomethacin (30 microM). 3. Adenosine 5'-triphosphate (ATP), alpha, beta-methylene ATP (alpha, beta-MeATP), beta, gamma-methylene ATP (beta, gamma-MeATP), 2-methylthio ATP (2-MeSATP) and uridine 5'-triphosphate (UTP) all concentration-dependently contracted the frog aorta. ATP and alpha, beta-MeATP were equipotent and more potent than UTP and beta, gamma-MeATP; 2-MeSATP had little activity. 4. The P2-purinoceptor antagonist, suramin (0.1 mM) inhibited contractions to alpha, beta-MeATP but not to ATP. Pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS; 30 microM) also inhibited contractions to alpha, beta-MeATP but not to ATP. Contractions to ATP were, however, inhibited by indomethacin (30 microM). 5. In conclusion, in the frog aorta there appears to be a novel subclass of P1-purinoceptor mediating vasodilatation, although like the A3 subclass it is not blocked by methylxanthines; a P2-purinoceptor mediates vasconstriction which resembles a P2x subtype, based on the agonist potency of alpha, beta-MeATP being more potent than 2-MeSATP (UTP has moderate activity) and PPADS is an effective antagonist. There is no evidence for the presence of a P2y-purinoceptor, mediating vasodilatation, in this preparation.

Adenosine↗

PubMed1996

The involvement of the endothelium in the relaxation of the leopard frog (Rana pipiens) aorta in response to acetylcholine.

1. The vasodilator response to acetylcholine (ACh) was investigated in the aortic arches of the leopard frog (Rana pipiens). 2. With adrenaline pre-constricted preparations, both ACh and sodium nitroprusside (SNP) caused concentration-dependent relaxations. Damage to the endothelial layer abolished relaxations to ACh, or reduced them greatly, but had no effect on vasodilatation to SNP. 3. NG-Nitro-L-arginine methyl ester (L-NAME; 1-100 microM) concentration-dependently inhibited relaxations in response to ACh, but had no effect on the ability of SNP to induce vasodilatation. 4. L-Arginine (L-Arg; 100-200 times the concentration of L-NAME) failed to reverse the inhibitory effect of L-NAME (1-100 microM) apart from one isolated instance. 5. In summary, this study has shown endothelium-dependent vasodilatation to ACh in an amphibian blood vessel that appears to be mediated via nitric oxide (NO). The response to ACh differs from many mammalian preparations in that the inhibitory effect of L-NAME could not be overcome by L-Arg, in addition to L-NAME itself having no direct effect upon the tone of the vessel.

Acetylcholine↗

PubMed1995

Effects of vitamin E deficiency on autonomic neuroeffector mechanisms in the rat caecum, vas deferens and urinary bladder.

1. Modified sucrose-gap, standard organ-bath techniques and transmitter release studies were used to examine neuromuscular transmission in the caecum, vas deferens and urinary bladder in normal rats and in rats maintained for 12 months on a diet free of vitamin E. 2. In the caecum circular muscle, non-adrenergic, non-cholinergic inhibitory junction potentials were absent from 48 and 15% of preparations from vitamin E-deficient and control animals, respectively. Cholinergic excitatory junction potentials were absent from 83 and 8% of vitamin E-deficient and control preparations, respectively. Responses to applied noradrenaline (0.1-30 microM), alpha,beta-methylene ATP (3-100 microM) and acetylcholine (0.1-30 microM) were attenuated or absent in vitamin E-deficient tissues. Responses to applied KCl were similar in both groups. Release of [3H]noradrenaline or endogenous acetylcholine could not be evoked from vitamin E-deficient tissues. 3. In contrast, in isolated preparations of the vas deferens and urinary bladder, neuromuscular transmission by adrenergic, cholinergic and purinergic components were unaffected by long-term vitamin E deficiency. 4. In conclusion, vitamin E deficiency causes dysfunction of autonomic neuroeffector mechanisms in the smooth muscle of the rat caecum, at both a pre- and postjunctional level. The lesions in autonomic transmission mechanisms brought about by long-term vitamin E deficiency were found only in the caecum; no changes in sympathetic neuromuscular transmission were observed in the vas deferens, or in parasympathetic neuromuscular transmission in the urinary bladder.

Adenosine Triphosphate↗

PubMed1995

Responses of the aorta of the garter snake (Thamnophis sirtalis parietalis) to purines.

1. Isolated aortic rings from the garter snake (Thamnophis sirtalis parietalis) were investigated in order to identify and classify responses to adenosine and adenosine 5'-triphosphate (ATP) and their analogues as part of a comparative study of vertebrate purinoceptors. 2. Adenosine, D-5'-(N-ethylcarboxamide) adenosine (NECA), R- and S-N6-(2-phenylisopropyl) adenosine (R- and S-PIA) and 2-chloroadenosine (2-CA) all concentration-dependently relaxed aorta preconstricted with noradrenaline (NA). The order of potency was: NECA > R-PIA = 2-CA > adenosine > S-PIA. Individual pD2 values for the analogues were: NECA 7.12 +/- 0.13 (9), R-PIA 5.93 +/- 0.25 (7), 2-CA 5.64 +/- 0.40 (5), adenosine 5.04 +/- 0.10 (13) and S-PIA 4.26 +/- 0.10 (7). The order of potency has characteristics of both A1 and A2 receptors and cannot satisfactorily be classified according to the P1-(adenosine) purinoceptor subtypes established in mammalian preparations. 3. ATP, alpha, beta-methylene ATP (alpha, beta-MeATP), 2-methylthio ATP (2MeSATP), beta, gamma-methylene ATP (beta, gamma,-MeATP) and uridine 5'-triphosphate (UTP) all concentration-dependently constricted the isolated aorta. The order of potency was alpha, beta-MeATP = 2MeSATP > ATP > beta, gamma-MeATP > UTP. Only ATP, alpha, beta-MeATP and 2MeSATP consistently produced a maximum response; pD2 values were: ATP 3.98 +/- 0.07 (10), alpha, beta-MeATP 5.86 +/- 0.15 (12) and 2MeSATP 6.06 +/- 0.23 (9). In vessels preconstricted with NA neither ATP nor 2MeSATP caused relaxation in the presence or absence of the endothelium. 4. Suramin (0.1 mM) inhibited vasoconstriction to ATP, alpha,beta-MeATP, 2MeSATP and beta,upsilon-MeATP;however, since contractions to ATP and analogues did not reach a maximum response in the presence of this and other antagonists, pD2 values could not be calculated.5. Pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS; 30 micro M), a P2x-purinoceptor antagonist,antagonized constrictions to alpha, beta-MeATP only. Reactive blue 2 (RB2; 30 micro M), a P2Y-purinoceptor antagonist, inhibited vasoconstrictions to 2MeSATP only.6. Indomethacin (30 micro M) inhibited vasoconstriction in response to ATP and 2MeSATP, but not alpha,beta,-MeATP, suggesting that the presence of an unaltered phosphate chain on the ATP analogue was necessary to stimulate the production of a prostanoid.7. Repeated administration of alpha,beta-MeATP (3 microM) caused desensitization of the receptor responsible for the constriction due to alpha,beta-MeATP whereas the responses to ATP and 2MeSATP were unaltered.8. In summary, both P1-purinoceptors mediating vasodilatation and P2-purinoceptors mediating vasoconstriction are present on the garter snake aorta. However, in contrast to mammalian vessels, bothP2x and P2Y subtypes mediate vasoconstriction. There was no evidence for vasodilatation to ATP or analogues. Stimulation of the P2-purinoceptor by ATP and 2MeSATP caused the synthesis of a prostanoid. In addition, the possibility of a receptor activated by ATP, separate from P2X and P2Y subtypes is discussed since contractions to ATP proved to be insensitive to both PPADS and RB2. A comparison is made of purinoceptors in the garter snake aorta with those in other vertebrate vessels.

Adenosine↗

PubMed1993

Identification of potent, selective P2Y-purinoceptor agonists: structure-activity relationships for 2-thioether derivatives of adenosine 5'-triphosphate.

Study of P2-purinoceptor subtypes has been difficult due to the lack of potent and selective ligands. With the goal of developing high affinity P2-purinoceptor-selective agonist, we have synthesized a series of analogues of adenine nucleotides modified on the purine ring as chain-extended 2-thioethers or as N6-methyl-substituted compounds. Chemical functionality incorporated in the thioether moiety included cyanoalkyl, nitroaromatic, amino, thiol, cycloalkyl, n-alkyl, and olefinic groups. Apparent affinity of the compounds for P2Y-purinoceptors was established by measurement of P2Y-purinoceptor-promoted phospholipase C activity in turkey erythrocyte membranes and relaxation of carbachol-contracted smooth muscle in three different preparations (guinea pig taenia coli, rabbit aorta, and rabbit mesenteric artery). Activity at P2X-purinoceptors was established by measurement of contraction of rabbit saphenous artery and of the guinea pig vas deferens and urinary bladder. All 11 of the 2-thioethers of ATP stimulated the production of inositol phosphates with K0.5 values of 1.5-770 nM, with an (aminophenyl)ethyl derivative being most potent. Two adenosine diphosphate analogues were equipotent to the corresponding ATP analogues. Adenosine monophosphate analogues were full agonists, although generally 4 orders of magnitude less potent. ATP 2-thioethers displayed pD2 values in the range of 6-8 in smooth muscle assay systems for activity at P2Y-receptors. There was a significant correlation for the 2-thioether compounds between the pK0.5 values for inositol phosphate production and the pD2 values for relaxation mediated via the P2Y-purinoceptors in the guinea pig taenia coli, but not for the vascular P2Y-receptors or for the P2X-receptors. At P2X-receptors, no activity was observed in the rabbit saphenous artery, but variable degrees of activity were observed in the guinea pig vas deferens and bladder depending on distal substituents of the thioether moiety. N6-Methyl-ATP was inactive at P2X-receptors, and approximately equipotent to ATP at taenia coil P2Y-receptors. This suggested that hybrid N6-methyl and 2-thioether ATP derivatives might be potent and selective for certain P2Y-receptors, as was shown for one such derivative, N6-methyl-2-(5-hexenylthio)-ATP.

Adenine Nucleotides↗

PubMed1993

Identification of purinoceptors in the isolated stomach and intestine of the three-spined stickleback Gasterosteus aculeatus L.

1. Adenine nucleosides and nucleotides were examined for pharmacological activity in isolated stomach and intestine from the stickleback Gasterosteus aculeatus L. 2. Adenosine and its stable analogues all concentration-dependently relaxed carbachol-contracted stomach and intestine, with no significant difference in the potency of the analogues. Only 8-(p-sulphophenyl) theophylline inhibited the relaxant response to adenosine in both tissues; other adenosine antagonists such as 1,3-dipropyl-8-cyclopentylxanthine were not active. 3. ATP, alpha, beta-methylene ATP (alpha, beta-MeATP) and 2-methylthio ATP (2-MeSATP) all caused concentration-dependent contractions of the stomach and intestine. 4. In the stomach, the order of potency was 2-MeSATP > alpha,beta-MeATP = ATP; the P2Y-purinoceptor antagonist reactive blue 2 inhibited responses to ATP. 5. In the intestine, the order of potency was alpha,beta-MeATP > 2-MeSATP = ATP; reactive blue 2 did not affect responses to ATP, nor did prolonged incubation with alpha,beta-MeATP. 6. It is concluded that in both the stomach and intestine, adenosine is acting through a non-specific or undifferentiated P1-purinoceptor. In the stomach, however, the P2-purinoceptor appears to be analogous to the mammalian P2Y-purinoceptor, and in the intestine, the receptor is more similar to the mammalian P2X-subtype, although it was not susceptible to desensitization.

Adenosine↗

PubMed1992

Quinacrine-staining of neurones, and activity of purine nucleosides and nucleotides in marine and terrestrial invertebrates from several phyla.

1. The acridine derivative quinacrine was used to stain nerve fibres in internal organs of 17 species of marine and terrestrial invertebrates from seven different phyla. 2. The majority of preparations showed quinacrine-stained nerve fibres. There was a degree of variation, ranging from a dense network of nerve bundles to single fibres. Quinacrine-positive nerve cell bodies were also observed in some ganglia. 3. Pharmacological experiments were performed on a variety of isolated tissues from the different marine and terrestrial groups, in order to ascertain their sensitivity to adenine nucleosides and nucleotides. 4. Correlation is drawn between the ability of neurones within a tissue to bind quinacrine, and the ability of that tissue to respond to applied adenine nucleosides and nucleotides.

Animals↗

PubMed1992

Responses of the rectum and oesophagus of the snail Helix aspersa to purine nucleotides and nucleosides.

1. Purine compounds were examined for pharmacological activity in the rectum and oesophagus of the garden snail Helix aspersa. 2. In the rectum, adenosine, AMP, ADP and ATP (above 10 microM) and acetylcholine (above 1 nM) consistently caused concentration-dependent contractions. The slope of the dose-response curve for ADP in the rectum was significantly steeper than for the other purine compounds. The contractile responses to the nucleotides and acetylcholine, but not adenosine, were selectively potentiated by physostigmine (1 microM). Atropine (1 microM) and tubocurarine (30 microM) failed to block the responses to the purines or acetylcholine. 3. In the oesophagus, adenosine, AMP, ADP and ATP (above 10 microM) and acetylcholine (above 1 nM) caused concentration-dependent contractions that were antagonised by atropine (1 microM). Tubocurarine (30 microM) failed to block the responses to the purine compounds or acetylcholine. Physostigmine (1 microM) potentiated the responses to ADP and acetylcholine but not ATP, AMP or adenosine. 4. In both the rectum and the oesophagus, the synthetic analogues of purine compounds including 2-chloroadenosine, alpha,beta-methylene ATP and 2-methylthio ATP were inactive up to a concentration of 100 microM. 5. Electrical field stimulation of the rectum and oesophagus produced consistent contractions which were unaffected by atropine (1 microM), tubocurarine (30 microM) or physostigmine (1 microM). These responses were not modulated by any of the purine compounds or their stable analogues. 6. The responses obtained appear novel even within known invertebrate purinergic systems, suggesting a differentiation of purinoceptor subtypes in this species.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗

PubMed1992

Effects of adenine nucleosides and nucleotides on the isolated heart of the snail Helix aspersa and the slug Arion ater.

1. Adenine nucleosides and nucleotides were examined for pharmacological activity in hearts isolated from the snail Helix aspersa and the slug Arion ater. 2. Adenosine, AMP, ADP and ATP (above 100 microM) produced either an excitation or an inhibition in the isolated hearts of the snail and slug. 3. 2-Chloroadenosine, alpha, beta-methylene ATP and 2-methylthio ATP were inactive at concentrations up to 1 mM. 4. Responses were not blocked by any commonly accepted vertebrate purinoceptor antagonists, indicating that these purinoceptors are dissimilar to vertebrate purinoceptors and cannot be classified according to accepted purinoceptor classifications. 5. Electrical field stimulation of the snail heart produced frequency-dependent responses: 1-4 Hz produced predominantly excitation, 8-32 Hz predominantly inhibition. These responses were unaffected by the purines up 3 mM.

Adenine Nucleotides↗

PubMed1990

Suramin antagonizes responses to P2-purinoceptor agonists and purinergic nerve stimulation in the guinea-pig urinary bladder and taenia coli.

1. Suramin, an inhibitor of several types of ATPase, was investigated for its ability to antagonize responses mediated via P2X-purinoceptors in the guinea-pig urinary bladder and P2Y-purinoceptors in the guinea-pig taenia coli. 2. In isolated strips of bladder detrusor muscle, suramin (100 microM-1 mM) caused a non-competitive antagonism of responses to alpha, beta-methylene ATP with an estimated pA2 of approximately 4.7, and inhibited responses to stimulation of the intramural purinergic nerves, with a similar pA2 value. At a concentration of 10 microM, suramin had little effect, but at a concentration of 1 microM, suramin potentiated responses to alpha,beta-methylene ATP, and potentiated responses to electrical stimulation of intramural purinergic nerves. 3. In isolated strips of taenia coli, in which a standard tone had been induced by carbachol (100 nM), suramin at 100 microM and 1 mM significantly antagonized relaxant responses to ATP (at an EC50 concentration) with an estimated pA2 of 5.0 +/- 0.82 and relaxant responses to electrical stimulation of the intramural non-adrenergic, non-cholinergic inhibitory nerves, either single pulses or trains of 8 Hz for 10 s, with estimated pA2 values of 4.9 +/- 0.93 and 4.6 +/- 1.01, respectively. Suramin had no significant effect at 1 or 10 microM. 4. Suramin, at any of the concentrations tested, did not affect contractile responses to histamine (10 microM) or carbachol (10 microM) in the bladder detrusor preparations. In the taenia coli, suramin did not affect either the relaxant responses to noradrenaline (at an EC50 concentration) or the contractile responses to carbachol (100 nM). 5. Thus, suramin at concentrations above 10 microM blocked actions mediated via P2x- and P2y-purinoceptors in the guinea-pig urinary bladder and taenia coli respectively. Potentiation of purinoceptor-mediated activity was seen only at a low concentration of suramin (1 microM) and only in the urinary bladder (P2x-purinoceptor). For its antagonistic activity suramin did not discriminate between P2X- and P2y-purinoceptors, but it was selective for P2-purinoceptor-mediated activity rather than that mediated via cholinoceptors, adrenoceptors or histamine receptors.

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