EFFECT OF TEMPERATURE ON SODIUM-CALCIUM EXCHANGE IN SARCOLEMMA FROM MAMMALIAN AND AMPHIBIAN HEARTS

We have investigated temperature dependence of Ca2+ uptake by the cardiac sarcolemmal Na+ -Ca2+ exchanger from dog, rabbit and bullfrog. In native rabbit sarcolemmal vesicles, Ca2+ affinity of the Na+ -Ca2+ exchanger is unchanged from 7 to 37-degrees-C; however, the initial velocity of Ca2+ uptake declines much more steeply below 22-degrees-C than above 22-degrees-C. In native dog sarcolemma, the temperature dependence of Na+-Ca2+ exchange velocity is similar to that of native rabbit. However, in frog heart the velocity of Na+-Ca2+ exchange declines much more slowly with decreasing temperature at both temperature ranges. Reconstitution of the Na+-Ca2+ exchanger into artificial lipid vesicles consisting of either asolectin or phosphatidylserine, phosphatidylcholine, and cholesterol has little effect on temperature dependence of Na+-Ca2+ exchange velocity in any of the three species. We conclude that the lesser temperature sensitivity of the cardiac sarcolemmal Na+-Ca2+ exchanger of a poikilothermic species is at least partly an intrinsic property of the transport protein.