The effect of temperature on the contractile response of cardiac muscle from two frog species, Rana temporaria and Xenopus laevis, at two different calcium concentrations—I. At pH 7.7

Abstract

1. 1. Mechanical parameters were recorded from paced ventricular cardiac muscle strips of two amphibian species, Rana temporaria and Xenopus laevis. 2. 2. The strips contracted at pH 7.7 and with either 1.6 or 3.0 mM Ca 2+ while the temperature was changed from 5 to 30°C. 3. 3. It is concluded that the cardiac muscles of the two frog species exhibited similar contractile responses upon temperature and Ca 2+ elevations at physiological pH, although X. laevis hearts displayed greater variation in tension response than those of R. temporaria. 4. 4. The relaxation mechanisms in relation to the contractile mechanisms of X. laevis myocardium, however, seemed to be more efficient, although more sensitive to low temperatures than those of R. temporaria.