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 language||English (US)|
|Number of pages||11|
|Journal||Annals of the New York Academy of Sciences|
|State||Published - 1991|
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)