Pre- and postjunctional adrenoceptor types in the circular muscle of the guinea-pig caecum |
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Authors: | W.M. Reilly C.H.V. Hoyle G. Burnstock |
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Affiliation: | (1) Department of Anatomy and Developmental Biology and Centre for Neuroscience, University College London, Gower Street, WCIE 6BT London, UK |
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Abstract: | Summary The sucrose gap technique was used to study the effects of applied adrenoceptor agonists on membrane potential and non-adrenergic, non-cholinergic inhibitory junction potentials (IJPs), in the smooth muscle of the circular coat of guinea-pig caecum. Noradrenaline (10 nmol/1–100 mol/l), phenylephrine (1–100 mol/l) and isoprenaline (0.1–100 mol/l) caused hyperpolarisations of the smooth muscle membrane which were rapid in onset and effect. The magnitudes of hyperpolarisations elicited by noradrenaline were significantly reduced by the non-specific -adrenoceptor antagonist phentolamine (10 gmol/l), the1-adrenoceptor antagonist prazosin (1 mol/l) and the -adrenoceptor antagonist propranolol (5 gmol/1). The 2-antagonist yohimbine (10 gmol/l) did not significantly reduce the magnitude of the hyperpolarisations induced by noradrenaline. Noradrenaline application caused a reduction in UP amplitude, during hyperpolarisation, by up to 50%. The reduction of the UP amplitude elicited by noradrenaline was significantly antagonised by yohimbine and phentolamine, but not by prazosin or propranolol. Clonidine caused a reduction of UP amplitude by up to 20%, but neither phenylephrine nor isoprenaline caused any significant reduction in UP amplitude. It is concluded that the hyperpolarising responses to exogenous noradrenaline in the circular muscle of guinea-pig caecum are mediated by postjunctional 1- and -adrenoceptors, and that the inhibition of UP amplitude is mediated by prejunctional 2-adrenoceptors.Send offprint requests to G. Burnstock at the above address |
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Keywords: | Noradrenaline Pre- and postjunctional adrenoceptors Guinea-pig caecum Circular muscle Neuromodulation |
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