GLUCOSE-6-PHOSPHATE STIMULATION OF MGATP-DEPENDENT CA-2+ UPTAKE BY RAT-KIDNEY MICROSOMES

(1) The features of MgATP-dependent Ca2+ accumulation under stimulation with glucose 6-phosphate were studied in rat kidney microsomes. (2) ca2+ accumulated in the presence of MgATP alone does not exceed approx. 2 nmol/mg protein. (3) Glucose 6-phosphate markedly stimulates ca2+ accumulation, up to steady-state levels approx. 15-fold higher than in its absence. (4) The hydrolysis of glucose 6-phosphate by glucose-6-phosphate is essential for the stimulation, as shown by inhibiting the glucose 6-phosphate hydrolysis with adequate concentration of vanadate. Inorganic phospate is accumulated in microsomal vesicles during glucose 6-phosphate-stimulated ca2+ uptake in equimolar amounts with respects to ca2+. (5) Increasing concentrations of glucose 6-phosphate result in increasing stimulations of ca2+ uptake, until a maximal ca2+-loading capacity of approx. 27 nmol/mg microsomal protein is reached. It is suggested that the enlargement of the kidney microsomal ca2+ pool induced by glucose 6-phosphate (an important metabolite in kidney) might play a role in the regulation of ca2+ homeostatis in kidney tubular cells. © 1990.