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Electrophysiological effects of Ca antagonists, tetrodotoxin, [Ca] o and [Na] o on myocardium of hibernating chipmunks: possible involvement of Na‐Ca exchange mechanism
Author(s) -
Kondo Noriaki
Publication year - 1987
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.1476-5381.1987.tb10286.x
Subject(s) - nitrendipine , nifedipine , tetrodotoxin , ryanodine receptor , electrophysiology , verapamil , chemistry , antagonist , medicine , endocrinology , biophysics , calcium , biology , receptor , biochemistry
1 The electrophysiological performance of myocardium of hibernating chipmunks was investigated in the presence of Ca antagonists and tetrodotoxin, and the effects of high [Ca] o and low [Na] o were examined. 2 The action potential of the preparations was characterized by the low amplitude of the plateau phase (APp). Ca antagonists, nifedipine (10 −6 m ) and nitrendipine (2 × 10 −6 m ), did not significantly inhibit this APp or the contraction. 3 These nifedipine‐insensitive electromechanical responses were completely abolished by an internal Ca release inhibitor, ryanodine. 4 Both increasing [Ca] o and lowering [Na] o , by replacing Na by lithium or choline, also inhibited APp. 5 Tetrodotoxin (10 −5 m ) which markedly inhibited the initial rapid phase of the action potential slightly affected APp. 6 These results suggest that the plateau potential of the present preparations is controlled by a process linked to Ca release from internal stores, most likely the Na‐Ca exchange mechanism.