Insulin and islet cell transplants: effects on diabetic rat cardiac myofibril ATPase

Streptozotocin-induced diabetes results in depression of growth rate, cardiac myofibril ATPase activity, and elevated plasma glucose levels. Reversibility of these changes with daily insulin injections and pancreatic islet cell transplants was investigated and compared. Cardiac myofibril ATPase activities (mumol Pi X mg-1 X min-1) were depressed in the uncontrolled diabetic (D) group over the complete range of Ca2+ concentrations tested (e.g., 0.057 +/- 0.017 at 10 microM free Ca2+) with respect to the control (C) group (0.113 +/- 0.009). Neither the transplanted (T) group (0.128 +/- 0.017) nor the insulin injected (I) group (0.111 +/- 0.014) was significantly different from the C animals. Normal growth rates were restored in both I and T groups, whereas in the D group weight gains were negligible in comparison. Cardiac myofibril protein yields (in mg/g wet wt) were not significantly different among groups. These findings indicate that both islet cell transplants and daily insulin injections are capable of normalizing plasma glucose levels, cardiac myofibril ATPase activity, and growth rates in STZ-diabetic rats.

Myosin isozyme distribution in rodent hindlimb skeletal muscle

The purpose of this study was to examine the distribution of myosin isozymes in rodent (Rattus norvegicus) hindlimb skeletal muscles and regions of muscle known to have contrasting fiber-type composition. Muscle samples were analyzed for Ca2+-regulated myofibril adenosine triphosphatase (ATPase) activity, Ca2+-activated myosin ATPase activity, myosin isozyme profile, and myosin light chain profile. Four isozymes of myosin were identified based on native protein and light chain electrophoresis patterns: one associated primarily with slow-twitch muscle (SM) and three associated primarily with fast-twitch muscle (FM). Multiple linear regression analysis of Ca2+-regulated myofibril ATPase activity (pCA 4) vs. measured isozyme profile was used to estimate the myofibril ATPase activities of the individual isozymes (FM1 = 0.86, FM2 = 0.52, FM3 = 0.31, and SM = 0.15 mumol Pi formed . mg myofibril protein-1 . min-1 at 25 degrees C, n = 180, P less than 0.001). Differences in the native isozyme profiles and myofibril ATPase activities between muscles and muscle regions of similar fiber type composition indicate that a given fiber type may not necessarily express a single isozyme profile. These data are consistent with the hypothesis that, among rodent hindlimb skeletal muscles and inherently their motor units, a range of myosin isozyme profiles exists that may provide a broad range of mechanical expression.

Effect of endurance swimming on rat cardiac myofibrillar ATPase with experimental diabetes

Diabetes is characterized by depressed cardiac functional properties attributed to Ca2+-activated ATPase activity. In contrast, endurance swimming enhances the cardiac functional properties and Ca2+-activated myofibril ATPase. Thus, the purpose of this study was to observe if the changes associated with experimental diabetes can be ameliorated with training. Diabetes was induced with a single i.v. injection of streptozotocin (60 mg/kg). Blood and urine glucose concentrations were 802 ± 44 and 6965 ± 617 mg/dL, respectively. The training control and training diabetic animals were made to swim (±2% body weight) 4 days/week for 8 weeks. Cardiac myofibril, at 10 μM free Ca2+ concentration was reduced by 54% in the sedentary diabetics compared with sedentary control animals (p < 0.05). Swim training enhanced the Ca2+-activated myofibril ATPase activities for the normal animals. The diabetic animals, which swam for 8 weeks, had further reduced their Ca2+-activated myofibril ATPase activity when compared with sedentary diabetics (p < 0.05). Similarly, the Mg2+-stimulated myofibril ATPase activity was depressed by 31% in diabetics following endurance swimming. It is concluded that the depressed Ca2+-activated myofibril ATPase activity of diabetic hearts is not reversible with endurance swimming.