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Two types of receptors for 5‐hydroxytryptamine on the cholinergic nerves of the guinea‐pig myenteric plexus
Author(s) -
Kilbinger H.,
PfeufferFriederich I.
Publication year - 1985
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1985.tb08890.x
Subject(s) - methysergide , myenteric plexus , ketanserin , acetylcholine , medicine , endocrinology , receptor , 5 ht receptor , tachyphylaxis , chemistry , reserpine , inhibitory postsynaptic potential , cholinergic , serotonin , receptor antagonist , biology , pharmacology , antagonist , immunohistochemistry
1 The effects of 5‐hydroxytryptamine (5‐HT) on spontaneous and electrically‐evoked release of [ 3 H]‐acetylcholine (ACh) from guinea‐pig myenteric plexus preparations preincubated with [ 3 H]‐choline have been investigated in the absence of cholinesterase inhibitors. 2 5‐HT caused a transient increase in spontaneous release and an inhibition of the electrically‐evoked release of [ 3 H]‐ACh. The 5‐HT‐induced contractions of the longitudinal muscle were clearly related to the increase in spontaneous release. The inhibitory effect was not due to activation of α‐adrenoceptors since it was also observed in the presence of tolazoline and on strips from reserpine‐pretreated guinea‐pigs. 3 After desensitization of the excitatory 5‐HT receptors with 5‐HT or metoclopramide the effects of 5‐HT on spontaneous [ 3 H]‐ACh release were largely reduced. A variety of established antagonists at neuronal 5‐HT receptors (i.e. metitepine 0.1‐1 μM; methysergide 1 μM; ketanserin 0.1‐1 μM; MDL 72222 0.1 μM; tropacocaine 1 μM) failed to block the excitation. 4 The inhibition by 5‐HT of the electrically evoked [ 3 H]‐ACh release was competitively antagonized by metitepine (pA 2 7.6) and methysergide (pA 2 7.0) but not by ketanserin. Tachyphylaxis to the inhibitory action of 5‐HT did not occur. 5 The results suggest that the excitatory 5‐HT receptor (‘M’‐receptor) differs in its pharmacological properties from other neuronal 5‐HT receptors. The presynaptically located inhibitory receptor may roughly correspond to the 5‐HT, receptor subtype but probably differs from the 5‐HT autoreceptor.