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A comparison between mechanisms of action of different nicotinic blocking agents on rat submandibular ganglia
Author(s) -
Large W.A.,
Sim J.A.
Publication year - 1986
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.1476-5381.1986.tb11159.x
Subject(s) - hexamethonium , decamethonium , chemistry , agonist , nicotinic agonist , pharmacology , acetylcholine , antagonist , nicotinic antagonist , cytisine , endocrinology , medicine , receptor , biochemistry , biology
1 The blocking properties of tubocurarine, decamethonium, hexamethonium and trimetaphan on nicotinic agonists applied by repetitive ionophoretic pulses were examined in rat submandibular ganglion cells using a two‐microelectrode voltage‐clamp technique at 30°C. 2 Hexamethonium, a proposed slowly dissociating, open‐channel blocker at concentrations of 2–20 μM did not produce a ‘use‐dependent’ run‐down of responses, but its antagonism was clearly dependent on membrane potential. 3 The voltage‐dependent reduction of agonist response by hexamethonium was not dependent on the nature of agonist used. Similar results were obtained with acetylcholine (ACh) and carbamylcholine (CCh) ionophoresis. 4 (+)‐Tubocurarine (5 μM) and decamethonium (10 μM) produced ‘use‐dependent’ run‐down of agonist responses which became more pronounced at higher frequency and as the cell was hyperpolarized, consistent with open‐channel blockade. In contrast, trimetaphan (2.5 μM), a receptor antagonist did not cause ‘use‐dependent’ run‐down of responses. 5 Hence, the antagonism produced by hexamethonium, unlike tubocurarine and decamethonium, could not be accounted for in terms of open‐channel blockade but requires an alternative mechanism, the nature of which is discussed.