Effects of temperature on rat and mouse cardiac myosin ATPase activity during development

Myosin was isolated from rat and mouse ventricular myocardium and examined during development at stages with known composition of myosin isoenzymes. The ATPase activity and its temperature dependence is the same in one-week-old and adult mouse ventricles. In rat heart myosin, the ATPase activity is low 18 days prenatally, high in 3-week-old animals and declines towards adulthood. ATPase activity of heart myosin from rat foetuses is more temperature dependent than that of three-week-old animals. These results strongly suggest that adaptation of the heart to development differs in the mouse and the rat and that the properties of mouse V1 isoenzyme do not change at the studied periods.