Effects of Ischemia on the Specific Activity of Ca++ - Mg++ -Activated ATPase in the Subcellular Fraction of Renal Tissues in Rabbits

Lee, Young Ho; Chai, Soo Eung

Abstract

Calcium has been implicated as a primary pathogenetic mediator of cellular injury under conditions of oxygen and substrate deprivation in the kidney aswell as other tissues. It has been proposed that calcium entry from the external medium increases intracellular free calcium to toxic levels there-by converting cellular injury from a potentially reversible to an irreversible state. Cellular calcium homeostasis is a fundamental prerequisite for many coordinate cellular functions. The regulation of cellular Ca++ -metabolism is maintained mainly by Ca++ -ATPase. The purpose of the present study was to determine the effects of ischemia on the subcellular specific activity of Ca++ -ATPase of renal tissues in the rabbits. 1. In both normal cortical and medullary tissues, the specific activities Ca++ -ATPase were higher in mitochondria than in cytosol. 2. In cortical tissue, the specific activities of mitochondrial Ca++ -ATPase were increased with duration of ischemic time under normothermia. But the specific activities were decreased comparing to those of control under hypothermia, and the activities were not different with those of control in Verapamil treated group. 3. The specific activities of Ca++ -ATPase of cortical cytosol were increased as in mitochondria under normothermia. And the activities were similar with those of control in hypothermic and Verapamil treated groups. 4. In medullary tissues, the specific activities of mitochondrial Ca++ -ATPase were increased with duration of ischemic time under normothermia. In Verapamil treated group, the activities were decreased comparing to those of control. And there was no difference of activities between hypothermia and control groups. 5. As in cortical tissues, the specific activities of Ca++ -ATPase of medullary, cytosol were increased in normothermic group. And the activities were similar with those of control in hypothermic and Verapamil treated groups. Above results suggested that calcium contents of mitochondria and cytosol were increased with duration of ischemic time under normothermia. Hypothermia and Verapamil treatment seemed to be beneficial effects in prevention of calcium accumulation in the renal tissues.