Nicardipine as a Ca2+ channel blocker in single barnacle muscle fibers.
A study has been made of the efficacy of nicardipine as a Ca2+ channel blocker by determining the magnitude of its effect on the stimulatory response of the ouabain-insensitive Na+ efflux in single barnacle muscle fibers to 100 mM external K+. The results show that nicardipine (at pH 6.5) is a potent inhibitor, the minimal effective concentration being approx. 10(-7) M and the IC(50) about 5.10(-6) M. Nicardipine, however, is not as potent as verapamil (at pH 6.5) on an equimolar basis. This is explained by assuming that the number of dihydropyridine receptors in the t-tubule membranes of barnacle fibers is not high or that verapamil is able to block the sarcoplasmic reticulum Ca2+ release channel in addition to the voltage-dependent Ca2+ channels.
Xie
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Department of Physiology, University of Wisconsin, Madison.
Bittar
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D000818:Animals; D015220:Calcium Channels / Q000187:drug effects* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D009132:Muscles / Q000187:drug effects / Q000378:metabolism*; D009529:Nicardipine / Q000494:pharmacology*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism; D001468:Thoracica / Q000187:drug effects / Q000378:metabolism*; D014700:Verapamil / Q000494:pharmacology
D015220:Calcium Channels; D010042:Ouabain; D012964:Sodium; D014700:Verapamil; D009529:Nicardipine; D011188:Potassium