Binding and effect of tritiated quinidine on cardiac subcellular enzyme systems: sarcomplasmic reticulum vesicles, mitochondria and Na+, K+- adenosine triphosphatase

HR Besch and AM Watanabe

A tritium-labeled derivative of quinidine (D3HQ) was used to assess binding and effect of this drug on isolated membrane preparations from myocardium. D3HG bound to sarcoplasmic reticulum vesicles (SRV) and diminished both Ca++ binding and Ca++ uptake activity. Binding of more than 19 nmol of D3HQ were required to displace 1 nmol of Ca++. Dual- wavelength spectrophotometric methods for monitoring the alterations in Ca++ binding showed that D3HQ depressed maximal Ca++ binding and hastened the onset of Ca++ release from Ca++-loaded SRV, but did not alter the maximal rate of Ca++ release. D3HG also diminished Ca++ sequestration by isolated cardiac mitochondria but the level of D3HQ binding did not correlate with the degree of inhibition. Binding of D3HQ to Na+, K+-adenosine triphosphatase also occurred to a limited extent and a partial inhibition of enzyme activity resulted. A reciprocal relationship between D3HQ binding and a decrease in functional activity of the subcellular membrane systems could be demonstrated only for SRV. The results suggest that cinchona alkaloids might affect myocardial contractility by their effects on Ca++ handling by SRV.

Volume 202, Issue 2, pp. 354-364, 08/01/1977
Copyright © 1977 by American Society for Pharmacology and Experimental Therapeutics

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