Effects of calcium and pH on the mechanical performance of heart muscle in the frog, Rana temporaria, during anoxia and subsequent recovery.

Abstract

Heart ventricular muscle strips from Rana temporaria recover their isometric contractile tension completely within 20 min of reoxygenation following an anoxic period of 60 min in a physiological solution at pH 7.6. Corresponding recovery at pH 6.6 is only 43% of pretreatment values. High calcium concentration during the period of anoxia at pH 6.6 and subsequent recovery, returns contractile tension to almost pre-anoxic values within 1 h. If, however, the calcium concentration is increased at the moment of reoxygenation, contractile tension is restored even faster than if high calcium levels were present during anoxia. The loss of contractile tension caused by anoxia is the same at both pH 7.6 and 6.6 with the same calcium concentration. Comparison of the velocity parameters between high and low calcium experiments always shows a greater difference for the contraction velocities than for the corresponding relaxation velocities, independently of the pH. The quotient of these two velocities is used as an index of their relative rate of change. The results are interpreted in terms of calcium and hydrogen ion competition at various subcellular structures and the different influences these ions may have on contractile tension and both contraction and relaxation velocities.