Species differences and the role of sodium-calcium exchange in cardiac muscle relaxation

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Abstract

During normal relaxation in rabbit, guinea-pig, and rat ventricular muscle, the Na-Ca exchange system competes with the SR Ca pump, with the former being responsible for about 20-30% of the Ca removal from the cytoplasm. Ca extrusion via Na-Ca exchange is E(m)-sensitive, whereas Ca uptake by the SR is not. Neither the sarcolemmal Ca-ATPase pump nor mitochondrial Ca uptake appear to contribute significantly to the decline of [Ca](i) during relaxation. Furthermore, the diastolic efflux of Ca from cardiac muscle cells appears to be primarily attributable to Na-Ca exchange and not the sarcolemmal Ca-ATPase pump. In rabbit ventricle Ca entry via Na- Ca exchange is favored thermodynamically during much of a normal twitch contraction and Ca extrusion occurs primarily between beats. In rat ventricle Ca efflux via Na-Ca exchange occurs during the contraction and net Ca influx may occur between beats. This fundamental difference in Ca fluxes during the cardiac cycle in rat versus rabbit ventricle may be a simple consequence of the shorter action potential duration and higher aNa(i) in rat ventricle (due to the effects of E(m) and [Na] and [Ca] gradients on Na-Ca exchange).

Original languageEnglish (US)
Pages (from-to)375-385
Number of pages11
JournalAnnals of the New York Academy of Sciences
Volume639
StatePublished - 1991

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)

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