Net transsarcolemmal Ca2+ shifts versus Ca/Ca exchange in guinea pig ventricular muscle

Abstract

Summary:We investigated the net transsarcolcmmal Ca 2+ shifts and Ca/Ca exchange by means of 45Ca in isolated, perfused ventricles of guinea pig heart treated with vanadate to inhibit ATP-drivcn sarcolemmal Ca 2+ pmnp. The heart was stimulated (at the rate of 6(l/rain) and perfuscd with a solution containing 45Ca for 60 min. Thereafter stimulation was stopped and either pcrfusion with radioactive solution was continued or the solution was exchanged for a non-radioactive one. in the first case, tissue 4SCa content (equivalent to the exchangeable Ca 2+ content) dropped from 1.960 _+ 0.120 mmol/kg of wet weight (w.w.) to 0.715 _+ 0.049 mmol/kg w.w. and stabilized at this level between 5th and 10th min. In the second case, decrease in 45Ca content continued and within 40 rain attained 0.047 _+ 0.004 mmol/kg w.w., despite stabilizing of the total exchangeable Ca 2+ content. Drop of 4-~Ca contcnt in the rested heart perfused (until the end of experiments) with radioactive solution resulted from the net transsarcolemmal Ca 2+ shift and it was strongly inhibited by removal of extracellular Na ~. The continuing drop in 45Ca content in the heart perfused with non-radioactive solution while total Ca 2+ content stabilized must have resulted from Ca/Ca exchange; it was stimulated by removal of extracellular Na +. These experiments separate two modes of 45Ca fluxes and suggest that a common route of these fluxes is the Na/Ca exchanger.