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.

Sodium and potassium permeability of membrane vesicles in a sarcolemma-enriched preparation from canine ventricle.

Vesicles in a highly enriched sarcolemma preparation from canine ventricle were found to develop membrane potentials in response to outwardly directed potassium and inwardly directed sodium concentration gradients. The magnitude of the potential measured by the fluorescent dye diS-C3-(5) suggested a sodium-to-potassium permeability ratio between 0.2 and 1.