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Inhibition of neuromuscular transmission in the myenteric plexus of guinea‐pig ileum by ω‐conotoxins GVIA, MVIIA, MVIIC and SVIB
Author(s) -
Hong S.J.,
Roan YowFen,
Chang C.C.
Publication year - 1996
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.1476-5381.1996.tb15470.x
Subject(s) - tetrodotoxin , stimulation , neuromuscular transmission , chemistry , acetylcholine , carbachol , medicine , endocrinology , pharmacology , anesthesia , biology
1 The effects of a number of Ca 2+ channel blockers on the transmural electrical stimulation or receptor agonist‐elicited contractile responses of guinea‐pig ileum were compared. 2 ω‐Conotoxins (MVIIA, GVIA, SVIB and MVIIC), but not ω‐agatoxin IVA, completely blocked the twitch responses evoked by low frequency (0.1 Hz) transmural stimulation without inhibition of the contractures evoked by exogenous acetylcholine. The concentration‐inhibition curves were shifted by changes of external Ca 2+ . 3 The tetanic contractures produced by a high frequency (30 Hz) train of stimulation were inhibited by ω‐conotoxins by only 25–30%, except for ω‐conotoxin MVIIC, which produced about 55% inhibition, all significantly less than that produced by atropine (about 70%) or tetrodotoxin (about 85%). Combinations of ω‐conotoxins did not produce additive inhibitory effects. 4 The four ω‐conotoxins as well as atropine produced similar partial inhibition (53–62%) of the contractures evoked by dimethylphenylpiperazinium, while tetrodotoxin inhibited the contracture completely. 5 Nifedipine and Ni 2+ depressed the nerve stimulation‐evoked twitch response and tetanic contracture as well as acetylcholine contracture. 6 These observations suggest that, in the myenteric plexus, a subset of N‐type Ca 2+ channel dominates under low frequency stimulation, while high frequency stimulation may recruit additional channels and non‐cholinergic pathways.