Temperature, pH and seasonal dependence of Ca-uptake and ATPase activity of white and red muscle microsomes

Abstract

The total Ca ++-uptake of fragmented sarcoplasmic reticulum (FSR) of either white or red skeletal muscle was optimal between pH 6.5–7.0 and 5.7–6.4 in the presence or absence of oxalate, respectively. Both the total Ca ++-uptake and the initial rate of uptake were considerably lower in red FSR than in white FSR. The Ca ++-uptake ability of either FSR showed seasonal variations; in the summer the activity was considerably less than during the winter or springtime. Under optimal conditions Ca ++-uptake in the absence of oxalate was 250 nmoles/mg for white and 40 nmoles/mg for red FSR; corresponding uptakes in the presence of oxalate were 6.0 and 1.2μmoles/ mg. The initial rates measured over the first seconds were 1.8 and 0.15μmoles/mg/min for white and red FSR, respectively, regardless whether oxalate was present or absent. The initial rate of the “basal” ATPase activity of particulate or solubilized red FSR was almost one order of magnitude higher than that of white FSR. The latter, however, showed a significant calcium dependence while the red FSR ATPase was insensitive to calcium. The temperature dependence of Ca ++-uptake was the same for the two types of FSR's; the activation energies were 11 and 25 kcal/mole in the absence and in the presence of oxalate, respectively. The activation energy of the hydrolysis of ATP in the absence of Ca ++ (basal ATPase) was the same for both FSR (11 kcal/mole); Ca ++ roughly doubled the activation energy for white, but had little or no effect on red FSR. 32P incorporation from γ- 32P-ATP was eight times less for red FSR than for white FSR.