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Mode of stimulatory actions of cadmium ion on the mouse diaphragm
Author(s) -
Fu W.M.,
LinShiau S.Y.
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.tb08884.x
Subject(s) - tetrodotoxin , acetylcholine , chemistry , carbachol , endocrinology , medicine , neuromuscular junction , biophysics , phrenic nerve , procaine , muscle contraction , caffeine , stimulation , biology , pharmacology , respiratory system , neuroscience
1 Effects of Cd 2+ on the phrenic nerve‐diaphragm preparation of the mouse varied markedly in media containing various Ca 2+ concentrations. In normal 2.5 mM Ca 2+ medium, Cd 2+ inhibited acetylcholine release from nerve endings without appreciable effect on the muscle membrane. However, Cd 2+ elicited stimulatory effects on the muscle membrane in low Ca 2+ medium (10 −3– 1 mM). These stimulatory effects included the induction of spontaneous contractions, augmentation of twitch responses to direct electrical stimulation and potentiation of the muscle contracture induced by acetylcholine, carbachol and high K + . By contrast, caffeine contracture was not affected by Cd 2+ . 2 Tetrodotoxin, procaine, cysteine and glycerol pretreatment abolished these stimulatory effects of Cd 2+ . Moreover, changing the ionic composition of the bathing medium to one containing low Na + , high K + , high Mg 2+ or high Ca 2+ also antagonized these effects of Cd 2+ . In contrast, low Mg 2+ markedly potentiated the frequency of spontaneous contractions induced by Cd 2+ . 3 (+)‐Tubocurarine and β‐bungarotoxin had no effect on Cd 2+ ‐induced spontaneous contractions indicating that they may be myogenic rather than neurogenic in origin. 4 By use of conventional microelectrodes, it was found that Cd 2+ not only depolarized the muscle membrane but also induced spontaneous action potentials at a high frequency (173 ± 17 Hz). 5 It is concluded that increased Na + permeability of the muscle membrane is the essential step bringing about spontaneous contractions. The binding of Cd 2+ to ‐SH groups of the membrane is closely related to the induction of these effects.