Rapid Publications Diabetes Mellitus Induces Changes in Cardiac Myosin of the Rat

'^ I. SUMMARY Decreased contractility has been reported in the diabetic heart. Because a close correlation exists between contractility and the activity of Ca ATPase of purified actinomyosin and myosin, Ca ATPase activity was determined in control and diabetic rats. In control rats, actinomyosin ATPase was 0.59 ± 0.05 /xmol Pi/mg protein/min and had decreased by 35% to 0.38 ± 0.04 in diabetic rats (P < 0.025). Myosin ATPase activity was 1.25 ± 0.09 /xmol Pi/mg protein/min in control rats and had decreased by 45% to 0.67 ± 0.05 in diabetic animals (P < 0.01). To investigate the decrease in myosin ATPase activity further, ventricular myosin was separated by pyrophosphate polyacrylamide electrophoresis into its three authentic components, V,, V2, and V3 myosin. V1 has the highest mobility and Ca ATPase activity (1.27 ± 0.3 arbitrary units) and represents 72% of control myosin, whereas V3 has the lowest mobility and Ca 2+ ATPase activity (0.16 ± 0.08 units) and constitutes 13% of myosin. A marked change in the predominance of V, and V3 myosin components occurs in diabetic rats where V3 myosin predominates, representing 68% of total myosin with V1 myosin constituting only 15%. Ca 2+ ATPase activities of V,, V2, and V3 myosin in control and diabetic hearts are similar; however, the predominance of V3 myosin in diabetic rats can account for the decreased Ca ATPase activity of diabetic myosin. The diabetes-induced changes in myosin ATPase activity and myosin isoenzyme distribution can be reverted to control levels by insulin administration. DIABETES 29: 579-582, July 1980.