Calcium fraction correlating with contractile force of ventricular muscle of guinea-pig heart

Abstract

Ca shifts in the isolated, perfused ventricular muscle of guinea-pig hearts were investigated with the aid of⁴⁵Ca under the conditions of complete equilibration of preparations with the isotope-containing solution. In some series of experiments total Ca content was also measured by means of atomic absorption spectrophotometry. The content of⁴⁵Ca at the end of 70 min equilibration period during which the ventricles were stimulated at a rate of 60/min was 1.66±0.09 mmol/kg w.w. This content dropped to 0.42±0.09 mmol/kg w.w. within 4 min of rest. Contractile force also decreased to 21% of control. Both the content of⁴⁵Ca and contractile force returned to the prerest values within the 4 min of post-rest stimulation. The difference between the total Ca content in the rested and stimulated muscle was comparable to the respective difference in⁴⁵Ca contents. A significant, linear correlation between this⁴⁵Ca fraction which was lost at rest and recovered during the postrest stimulation, and contractile force was found under the following experimental conditions: I. post-rest recovery, II. decay during rest, III. post-rest stimulation at various rates. These results are consistent with the hypothesis proposing that this Ca fraction is involved in the frequency-dependent control of contractile force.