title: The relationship of mechanical Vmax to myosin ATPase activity in rabbit and marmot ventricular muscle.
abstract: Papillary muscle mechanics and ventricular myosin calcium-activated ATPase activity were measured in the same heart as a function of temperature (8--28 degrees) in rabbits and marmots, in order to examine further the hypothesis that the velocity of cardiac muscle shortening at zero load (Vmax) is correlated with myosin ATPase activity. There was a similar Q10 for Vmax 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 rabbit Vmax 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 less than 0.01 (ANOV)]. Furthermore, the correlation proved to be predictive of cardiac Vmax 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 between Vmax and myosin ATPase defined here may prove to be predictive of the ability of cardiac muscle to release bond energy.
mesh_terms: D000818:Animals; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D066298:In Vitro Techniques; D008392:Marmota; D009200:Myocardial Contraction; D009206:Myocardium / Q000201:enzymology*; D009218:Myosins / Q000378:metabolism; D010210:Papillary Muscles / Q000201:enzymology / Q000502:physiology; D011817:Rabbits
chemical_list: D009218:Myosins; D000252:Calcium-Transporting ATPases