The effects of inhibition of the sarcolemmal Ca-ATPase on systolic calciumfluxes and intracellular calcium concentration in rat ventricular myocytes

The effects of carboxyeosin. an inhibitor of the sarcolemmal Ca-ATPase, wer e studied on intracellular Ca and membrane currents in isolated rat ventric ular myocytes. In the absence of carboxyeosin, 150-ms-duration depolarizing pulses from -40 to 0 mV resulted in an L-type Ca current on depolarization and a Na-Ca exchange "tail" current on repolarization. The calculated entr y of Ca on the L-type current was 1.3 times greater than the efflux via the Na-Ca exchange. The addition of carboxyeosin (20 mu M) resulted in either an increase of the Na-Ca exchange current or a decrease of the L-type Ca cu rrent such that the Ca entry and efflux were exactly equal. These results s uggest that, under control conditions, a carboxyeosin-sensitive Ca-ATPase c ontributes about 24% of the total Ca efflux from the cell and, therefore, t hat the sarcolemmal Ca-ATPase has a significant role in regulation of sarco lemmal Ca fluxes.