Calcium fraction correlating with contractile force of ventricular muscle of guinea-pig heart
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.
Key wordsHeart muscle Calcium Force-frequency relations
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