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

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 similarQ₁₀ 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,P<0.01 (ANOV)]. Furthermore, the correlation proved to be predictive of cardiacV_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.This work was supported in part by National Science Foundation Grant No. 1971-122; American Heart Association Grant No. 71 1080; Vermont Heart Association Grant Nos. AG71, 1971–1973, 1973–1974; PHS Nos. 16858 and AM 15594, and University of Vermont, College of Medicine General Research Support Grant No. RR05429. B. B. Hamrell was the recipient of a Special Research Fellowship, National Institutes of Health, National Institute of General Medical Sciences, 1F3GM39, 62301.