TEMPERATURE AND RELATIVE CONTRIBUTIONS OF CA TRANSPORT-SYSTEMS IN CARDIAC MYOCYTE RELAXATION

The relative contributions of the different Ca transport-systems invol ved in cardiac relaxation were evaluated at 25 and 35 degrees C in iso lated rabbit, ferret, and cat ventricular myocytes during twitches, ca ffeine-induced contractures in normal Tyrode solution, and caffeine-in duced contractures in Na- and Ca-free solution. The time course of int racellular [Ca] decline during these contractions in rabbit ventricula r myocytes allowed estimates of the relative contributions of the sarc oplasmic reticulum (SR) Ca pump, Na/Ca exchange, sarcolemmal Ca pump, and the mitochondrial calcium uniporter (with the latter two considere d together as ''slow mechanisms''). The percent contributions of the S R Ca pump, the Na/Ca exchange, and the slow mechanisms were 70, 27, an d 3% at 25 degrees C and 74, 23, and 3% at 35 degrees C. Warming from 25 to 35 degrees C decreases twitch contractions in rabbit and ferret myocytes and caffeine-induced contractures in normal Tyrode solution a nd Na- and Ca-free solution in all species. In contrast, in cat myocyt es warming increased twitches, possibly because of a stronger effect o f temperature on Ca influx. We conclude that increased temperature acc elerates all of the Ca transport systems involved in relaxation. Despi te large changes in each Ca transport system with warming, the relativ e contributions during relaxation remain similar at physiological temp erature.