EFFECTS OF TEMPERATURE AND OUABAIN ON THE RATE OF ACTION OF CALCIUM ON ATRIAL CONTRACTIONS1

SABATINI-SMITII, SANDRA AND WILLIAM C. HOLLAND: Effects of temperature and ouahain on the rate of action of calcium on atrial contractions. J. Pharmacol. Exp. Therap. 158: 22-27, 1967. When heating left atria were transferred from normal Ringer’s solution to one containing low calcium (2.4 to 0.24 mM CaCl2), isometric (ontractile tension de(hncd to:t new steady state level exponentially in time in one phase only. Increases of heart rate and temperature and pretreatment with 5 X 10 M ouabain accelerated the rate of decline without changing the exponential nature of the process. Temperature coefficients (Qio) ranged from 1.5 to 2.9 for control atria. being highest at the lower ranges of temperature and heart rate. values for ouahain varied from 1.3 to 1.4 and were not greatly in-fluenced by the heart rates and temperatures examined. These findings are consistent with the hypothesis that the time course of tension change due to an altered external calcium concentration reflects a quantity of calcium taken up reversibly by the heart muscle as tension changes. The rate-limiting step or steps governing this movement of cellular cal-cium appeared to he more of a physical, rather than a chemical, nature. The rates of thes