n(6)-cyclohexyladenosine and alpha-beta-methyleneadenosine-5--triphosphate

The effects of some agonists acting at P2 purinoceptors on guinea-pig isolated ileum longitudinal smooth muscle have been examined. The preparation contracted in response to ATP, alpha,beta-methylene ATP and 2-methylthio ATP, but not UTP. In this respect, alpha,beta-methylene ATP and 2-methylthio ATP were approximately equipotent and both were 10-50 times more active than ATP. Responses to alpha,beta-methylene ATP, but not 2-methylthio ATP or ATP, were antagonised by atropine and tetrodotoxin, suggesting that alpha,beta-methylene ATP activates cholinergic nerves in the ileum, whilst the other two compounds act on the smooth muscle. Two other purine nucleotide analogues, beta,gamma-methylene ATP and beta,gamma-imido ATP, did not cause contraction. However, both compounds antagonised responses to alpha,beta-methylene ATP, but not those to 2-methylthio ATP. Suramin antagonised responses to both alpha,beta-methylene ATP and 2-methylthio ATP, whilst Cibacron blue was without effect on responses to either agonist. We conclude that the purinoceptor on cholinergic nerves has some of the characteristics of the P2x purinoceptor, whilst the purinoceptor on ileal smooth muscle has some of the characteristics of the P2Y purinoceptor. However, further work will be necessary before definitive classification is possible.

Topics: Adenosine; Adenosine Triphosphate; Animals; Atropine; Guinea Pigs; Ileum; In Vitro Techniques; Male; Muscle, Smooth; Receptors, Purinergic P2; Suramin; Tetrodotoxin; Triazines; Uridine Triphosphate

1. In the pelvic plexus-vas deferens preparation of the guinea-pig, conditioning stimulation of the pelvic nerves depressed the phasic component of biphasic contractions evoked by test stimulation of the hypogastric nerves, but potentiated the tonic component. 2. Similarly, in the deganglionated vas deferens preparation, conditioning stimulation applied directly to postganglionic nerves issuing from the pelvic nerve side of the pelvic plexus depressed the phasic component of biphasic contractions evoked by test stimulation of the nerves issuing from the plexus on the side of the hypogastric nerve, but potentiated the tonic component. 3. In the deganglionated preparation in the presence of alpha,beta-methylene adenosine 5'-triphosphate (alpha,beta-mATP) by which the phasic component was removed, test contractions were markedly reduced by phentolamine and prazosin, and potentiated in a manner dependent on the magnitude of conditioning stimulation. 4. In the deganglionated preparations that were persistently exposed to alpha,beta-mATP (5-10 microM), attempts were made to identify the substance(s) mediating the potentiation of the prazosin-sensitive contractions and their sites of action. 5. Noradrenaline and neuropeptide Y depressed the test contractions. 6. ATP, adenosine 5'-diphosphate, adenosine 5'-monophosphate and adenosine potentiated the contractions. Inosine and adenine were without effect. The effect of ATP was antagonized by 8-phenyltheophylline. N6-Cyclohexyladenosine (CHA) potentiated the contractions in a dose-dependent and 8-phenyltheophylline-sensitive manner. 7. The conditioning stimulation-induced potentiation of test contractions was antagonized by 8-phenyltheophylline, but was further increased by dipyridamole. 8. Methoxamine-evoked contractions were potentiated by conditioning stimulation of the nerves in a manner antagonized by 8-phenyltheophylline, and also by CHA. 9. Adenosine and CHA inhibited in an 8-phenyltheophylline-sensitive manner field stimulation-induced release of 3H-activity from deganglionated vas deferens preloaded with [3H]noradrenaline. 10. In the deganglionated preparation that was not exposed to alpha, beta-mATP, ATP-evoked contractions were potentiated by conditioning stimulation and by CHA. 11. It is indicated that conditioning stimulation and adenosine exert opposite actions on phasic and on tonic contractions in spite of the results showing that each of them postjunctionally potentiates the responses to both ATP an

Topics: Adenosine; Adenosine Deaminase; Adenosine Triphosphate; Animals; Denervation; Dipyridamole; Electric Stimulation; Guinea Pigs; In Vitro Techniques; Male; Muscle Contraction; Receptors, Purinergic; Vas Deferens

1. In the guinea-pig pelvic plexus-vas deferens preparation, stimulation of the parasympathetic pelvic nerves contracted the vas deferens then depressed the contractile responses to stimulation of the sympathetic hypogastric nerves. 2. The contraction caused by stimulation of the pelvic nerves was initially phasic then tonic. The contractions were almost abolished by application of hexamethonium to the plexus. The phasic contraction was abolished by alpha,beta-methylene adenosine triphosphate applied to the vas deferens. 3. Conditioning stimulation of the pelvic nerves preferentially depressed the phasic component of test contractions evoked by hypogastric nerve stimulation but did not affect the compound action potentials in postganglionic nerves evoked by test stimulation. 4. When the pelvic plexus was divided into two parts, one with the pelvic nerves and the other with the hypogastric nerves, conditioning stimulation of the pelvic nerves still depressed test contractions evoked by hypogastric nerve stimulation. 5. In the de-ganglionated vas deferens preparation, conditioning stimulation of some postganglionic nerves also depressed contractions evoked by test stimulation of the other postganglionic nerves. 6. 8-Phenyltheophylline (5-20 microM) applied to the vas deferens antagonized the conditioning stimulation-induced depression in both the pelvic plexus-vas deferens and the de-ganglionated preparations. 7. N6-Cyclohexyladenosine (CHA) and N6-(L-2-phenylisopropyl)-adenosine at 0.5 microM preferentially inhibited phasic contractions evoked by the postganglionic nerve stimulation. The effect of CHA was antagonized by 8-phenyltheophylline (10 microM). 8. The results indicate that the mechanism underlying the conditioning stimulation-induced depression of phasic contractions operates not in the ganglia, but through activation of adenosine receptors in the vas deferens.

Topics: Action Potentials; Adenosine; Adenosine Triphosphate; Animals; Guinea Pigs; In Vitro Techniques; Male; Muscle Contraction; Parasympathetic Nervous System; Pelvis; Receptors, Purinergic; Sympathetic Nervous System; Theophylline; Time Factors; Vas Deferens