Influence of fasting and alloxan-diabetes on cardiac actomyosin and subcellular phosphorus levels



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Studies were undertaken to determine whether cardiac actomyosin and subcellular phosphorus fractions are altered in adult male Long- Evans rats which were fasted or injected with alloxan. The duration of fasting and of the diabetic state was investigated over a period of five days (fasting), and over 3,7, 14, 30, 60, 90, 120, 210 days (alloxan- diabetes). Actomyosin was determined by viscosimetric methods and as percent of total protein. The following cell fractions were isolated for total inorganic phosphorus determinations: total homogenate, supernatant (cytoplasm), nuclei-myofibrillar, mitochondrial, and microsomal. Fasting: Blood glucose decreased immediately, subsequently to rise toward normal levels by the third day of fasting; heart/body weight ratios followed an inverse pattern simultaneously. Actomyosin, as measured by ATPase activity (ATP sensitivity), was not significantly altered during the five day starvation period. Phosphorus in the homogenate fraction was significantly reduced at day three of fasting, while phosphorus in the other subcellular components was not significantly altered during the fasting period. Alloxan-diabetes: Fed blood glucose ranged from 395-550 mg%; heart/ body weight ratios increased and then returned toward normal by the end of the observation period. ATP sensitivity was not significantly altered, except during the first week following alloxan administration. There were slight but significant reductions and increases in inorganic phosphorus in the various subcellular compartments during the duration of alloxan-diabetes. These reductions occurred in the homogenate fraction at days 30, 60, 90, and 120; in the supernatant fraction at days 30 and 60; in the nuclei-myofibrillar fraction at days 60 and 120; in the mitochondrial fraction at days 3, 7, 30, and 60; and in the microsomal fraction at day 7. The slight increases occurred in the supernatant and microsomal fractions at days 14 and 90, respectively. Characterization of the actomyosin, as a criterion of purity, was determined by disc electrophoresis and ultra-centrifugal analysis.