Net transsarcolemmal Ca2+ shifts versus Ca/Ca exchange in guinea pig ventricular muscle.
We investigated the net transsarcolemmal Ca2+ shifts and Ca/Ca exchange by means of 45Ca in isolated, perfused ventricles of guinea pig heart treated with vanadate to inhibit ATP-driven sarcolemmal Ca2+ pump. The heart was stimulated (at the rate of 60/min) and perfused with a solution containing 45Ca for 60 min. Thereafter stimulation was stopped and either perfusion with radioactive solution was continued or the solution was exchanged for a non-radioactive one. In the first case, tissue 45Ca content (equivalent to the exchangeable Ca2+ 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 min attained 0.047 +/- 0.004 mmol/kg w.w., despite stabilizing of the total exchangeable Ca2+ content. Drop of 45Ca content in the rested heart perfused (until the end of experiments) with radioactive solution resulted from the net transsarcolemmal Ca2+ 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 Ca2+ 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.
Wolska
B M
BM
Department of Clinical Physiology, Medical Center of Postgraduate Education, Warsaw, Poland.
Lewartowski
B
B
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D006168:Guinea Pigs; D006352:Heart Ventricles; D006706:Homeostasis; D007474:Ion Exchange; D007700:Kinetics; D009206:Myocardium / Q000378:metabolism*; D012508:Sarcolemma / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology
D012964:Sodium; D002118:Calcium