Effect of hypocalcemia on divalent cation-activated ATPase and Ca²⁺ uptake in microsomes of rat kidney cortex

Effects of hypocalcemia on Ca²⁺ metabolism of microsomes from rat kidney cortex were studied. Microsomal activities of Ca²⁺-ATPase, Mg²⁺-ATPase and (Na⁺+K⁺)-ATPase increased 30-33 days after Ca²⁺ restriction or low Ca²⁺ vitamin D depletion, but alkaline phosphatase activity decreased. Calcium repletion in diet and injection of 1α-hydroxycholecalciferol or 1,25-dihydroxycholecalciferol were partially successful in returning Ca²⁺-ATPase and Mg²⁺-ATPase activity, but not (Na⁺+K⁺)-ATPase and alkaline phosphatase activity, to normal. Correlations between serum Ca²⁺ level and both ATPase activities were significant. ATP-dependent Ca²⁺ uptake of microsomes was not affected by hypocalcemia and vitamin D metabolites.