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

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Abstract
Heart ventricular muscle strips from R. 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 43% of pretreatment values. High Ca 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 the Ca concentration is increased at the moment of reoxygenation, contractile tension is restored faster than if high Ca levels were present during anoxia. The loss of contractile tension caused by anoxia is the same at pH 7.6 and 6.6 with the same Ca concentration. Comparison of the velocity parameters between high and low Ca experiments always shows a greater difference for the contraction velocities than for the corresponding relaxation velocities, independently of the pH. The quotient of these 2 velocities is used as an index of their relative rate of change. The results are interpreted in terms of Ca and hydrogen ion competition at various subcellular structures and the different influences these ions may have on contractile tension and contraction and relaxation velocities.