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Calcium channels and intracellular calcium release are pharmacologically different in frog skeletal muscle.
Author(s) -
McCleskey E W
Publication year - 1985
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1985.sp015643
Subject(s) - nifedipine , intracellular , biophysics , chemistry , verapamil , extracellular , contraction (grammar) , channel blocker , membrane potential , membrane channel , calcium , muscle contraction , calcium channel , voltage dependent calcium channel , endocrinology , membrane , biology , biochemistry , organic chemistry
The pharmacology of Ca2+ channels and intracellular Ca2+ release from the sarcoplasmic reticulum (s.r.) were compared by injecting Ca2+ channel blockers into the cytoplasm and observing contraction under voltage clamp of frog skeletal muscle fibres, a preparation that contracts only in response to Ca2+ release from the s.r. A method for quantifying intracellular injections by co‐injecting a fluorescent dye is described. Nifedipine injected into cells blocks Ca2+ current through the cell membrane showing that nifedipine is active when applied to the cytoplasmic side of the membrane in which Ca2+ channels are located. Neither the presence of Ca2+ channel blockers in the extracellular medium nor 24 h incubation in nifedipine and D‐600 affect contraction. Nifedipine and D‐600 injected to intracellular concentrations much greater than necessary to block Ca2+ channels do not affect contraction. The presence of 30 microM‐D‐600 during K+ contractures caused paralysis but 20 microM‐nifedipine did not. Thus, contracture‐dependent D‐600 paralysis is not due to blockade of the transverse tubule Ca2+ channel. It is concluded that: (a) a functioning Ca2+ channel on the cell membrane is not necessary to trigger Ca2+ release from the s.r.; (b) s.r. Ca2+ release and Ca2+ channels are pharmacologically different.