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Pharmaco‐mechanical coupling in the response to acetylcholine and substance P in the smooth muscle of the rat iris sphincter
Author(s) -
Banno Hitoshi,
Imaizumi Yuji,
Watanabe Minora
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.tb11090.x
Subject(s) - acetylcholine , cholinergic , contraction (grammar) , stimulation , substance p , chemistry , muscle contraction , medicine , endocrinology , sphincter , extracellular , biophysics , capsaicin , free nerve ending , electrophysiology , anatomy , biology , neuropeptide , biochemistry , receptor
1 In the rat iris sphincter muscle contractile responses to transmural stimulation consisted of two components, a fast cholinergic followed by a slow non‐adrenergic, non‐cholinergic (NANC) one. The magnitude of the latter varied widely and was on average 5% of that of the cholinergic component. 2 Exogenous substance P (1 nM‐1 μM) produced a concentration‐dependent contraction, the maximum amplitude of which was as large as that produced by acetylcholine (ACh). 3 Capsaicin (10 μM) induced a transient contraction only once in each preparation. After the treatment with capsaicin the NANC component disappeared. 4 Neither nerve nor direct electrical stimulation with short pulses elicited any active change in the membrane potential under physiological conditions, but an action potential was triggered by direct stimulation when the extracellular Ca ion was totally replaced by Ba ion. Under the latter conditions spontaneous spike potentials occurred repetitively. 5 ACh and substance P produced a large contraction without modifying the membrane potential. This was also the case in the presence of 5 mM Ba. 6 These results suggest that substance P‐ergic innervation may have a far lesser physiological significance than that which has been described in rabbits and that pure pharmaco‐mechanical coupling is characteristic of the responses to acetylcholine, substance P, and nerve stimulation in the rat iris sphincter muscle.