Original Articles

Influence of tetrandrine on positive inotropic action of isoproterenol and CaCl2 and on excitation-contraction coupling in isolated cat papillary muscles

Authors: Man-wen Jin, Da-chao Fang, Ming-xing Jiang

Abstract

The effects of tetrandrine, verapamil, propranolol and practolol on isoproterenol dose-response relationships and the influence of tetrandrine, verapamil and nifedipine on calcium dose-response relationships and on excitation-contraction coupling were investigated on isolated cat papillary muscles.
Propranolol and practolol competitively antagonized isoproterenol. Tetrandrine and verapamil also antagonized isoproterenol but in a non-competitive manner.
Tetrandrineļ¼Œverapamil and nifedipine shifted calcium dose-response curves to the right, and acted as non-competitive antagonists of calcium, as a plot of log (x-1) vs -log [B] resulted in straight lines with slopes of -0.43, -0.55 and -0.42, respectively.
Tetrandrine, verapamil and nifedipine resulted in excitation-contraction uncoupling. It was suggested that tetrandrine inhibited the inward diplacement of calcium through the voltage-dependent channel.
The results support our speculation that tetrandrine is a calcium antagonist of plant origin.
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