Routes of Calcium Flux in Cardiac Sarcoplasmic Reticulum
Net release of Ca2+ from the sarcoplasmic reticulum (SR) plays an important role in coupling excitation to contraction in cardiac muscle cells, and the uptake of Ca2+ by SR plays a major role in effecting relaxation of the contractile apparatus [9,20,26]. There are several possible routes of Ca2 + influx and efflux in SR that could account for the net uptake and release of Ca2+. These putative pathways include passive diffusion, pump-mediated Ca2+ influx and efflux, carrier-mediated facilitated diffusion, and Ca2+ efflux through a gated channel. One goal of research in this field is to identify the routes of Ca2+ flux in SR and to determine their magnitude, time course, and roles in physiological regulation of Ca2+ flux. In this presentation, the routes of Ca2+ flux in SR vesicles isolated from dog hearts are examined. The results suggest that Ca2+ fluxes in cardiac SR occur through only three routes: (1) forward pump-mediated Ca2+ influx; (2) reverse pump-mediated Ca2+ efflux; and (3) passive efflux.
KeywordsPermeability Hydrolysis Crystallization Sucrose Adenosine
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