The relationship of mechanicalV max to myosin ATPase activity in rabbit and marmot ventricular muscle

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Abstract
Papillary muscle mechanics and ventricular myosin calcium-activated ATPase activity were measured in the same heart as a function of temperature (8–28°) in rabbits and marmots, in order to examine further the hypothesis that the velocity of cardiac muscle shortening at zero load (V max) is correlated with myosin ATPase activity. There was a similarQ 10 forV max in each muscle type, as measured with isotonic afterloaded quick-releases at 30–33% time-to-peak tension; the calcium activated ATPase of myosin in the two muscle types also was similar. The least squares linear regression of rabbitV max on calcium-activated myosin ATPase activity was the same as in the marmot, so all the data were pooled to yield a linear regression (Y=0.47+3.82X) with a high correlation between the two variables [r=0.95,PV max and myosin ATPase activity levels in other experiments where these two measurements decreased below normal as a result of hypertrophic growth. Consequently, the quantitative relationship betweenV max and myosin ATPase defined here may prove to be predictive of the ability of cardiac muscle to release bond energy.