Abstract
Microsomes isolated from canine submandibular glands were examined for ATP-dependent calcium accumulation and calcium release. Calcium uptake (10 to 20 nmoles per min per mg protein at 37 °C) was linear with time up to 20 min and with the amount of microsomal protein in the range of 15 to 200 μg/ml of incubation medium. Of the nucleotide triphosphates tested, only adenosine triphosphate (ATP) supported calcium accumulation. Ruthenium red and ethacrynic acid, at concentrations of 90 μg/ml and 10 −4 M respectively, almost completely inhibited calcium uptake. Metabolic inhibitors such as 2,4 dinitrophenol, azide and oligomycin only partially affected microsomal calcium uptake. Incubation of prelabelled microsomes in a calcium-free solution resulted in the release of calcium at a rate of 0.025/min. The rate was decreased at 0 °C and by inclusion of 4.5 mM ATP in the medium. Addition of 2 mM calcium or removal of magnesium also reduced release. Ruthenium red at a concentration that decreased calcium uptake by greater than 90 per cent did not affect calcium outflow; whereas ethacrynic acid (5 × 10 −4M) induced a significant increase in calcium loss.
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