BINDING AND EFFECT OF TRITIATED QUINIDINE ON CARDIAC SUBCELLULAR ENZYME-SYSTEMS - SARCOPLASMIC-RETICULUM VESICLES, MITOCHONDRIA AND NA+, K+-ADENOSINE TRIPHOSPHATASE

  • 1 January 1977
    • journal article
    • research article
    • Vol. 202  (2) , 354-364
Abstract
A 3H-labeled derivative of quinidine (D3HQ) was used to assess binding and effect of this drug on isolated membrane preparations from myocardium [dog]. D3HQ bound to sarcoplasmic reticulum vesicles (SRV) and diminished both Ca2+ binding and Ca2+ uptake activity. Binding of more than 10 nmol of D3HQ were required to displace 1 nmol of Ca2+. Dual-wavelength spectrophotometric methods for monitoring the alterations in Ca2+ binding showed that D3HQ depressed maximal Ca2+ binding and hastened the onset of Ca2+ release from Ca2+-loaded SRV, but did not alter the maximal rate of Ca2+ release. D3HQ also diminished Ca2+ 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+ -ATPase [calf and dog heart] 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. Cinchona alkaloids might affect myocardial contractility by their effects on Ca2+ handling by SRV.

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