Cardiac [formula omitted] ATPase activity and its relation to myocardial glutathione status: Studies in the rat

Abstract

Cardiac Na + K + ATPase (which has previously been suggested to be regulated by a thiol-dependent process) is inactivated during ischemia. Moreover, myocardial glutathione (which controls the redox state of protein-thiol groups) is depleted during ischemia and thus may contribute to the changes in Na + K + ATPase activity. The objectives of the present study were to use the rat to: (1) pharmacologically manipulate myocardial glutathione to mimic ischemia-reperfusion-induced glutathione depletion and (2) determine (in the absence of ischemia) the relationship between myocardial glutathione content and Na + K + ATPase activity. Tissue glutathione was depleted by injecting rats with diethylmaleate (0, 55, 110, 215, 430 or 860 mg/kg; i.p.) 30 min before study. Total glutathione content fell from 1.72±0.03 to 1.66±0.04, 1.50±0.05, 0.93±0.03, 0.23±0.04 and 0.21±0.02 μmol/g wet weight, respectively. There was a linear correlation ( r=0.96) between Na + K + ATPase activity and glutathione content in diethylmaleate-treated animals. A separate group of animals were treated with phorone (0, 25, 50, 100, 150, 200 or 250 mg/kg; i.p. 120 min before study) which also depletes glutathione. Myocardial glutathione fell from its control value of 1.74±0.03 to 1.52±0.04, 1.35±0.06, 1.14±0.05, 0.84±0.04, 0.64±0.04, 0.54±0.03 μmoles/g wet weight, respectively. In these animals Na + K + ATPase activity was also linearly-related ( r=0.98) to glutathione content. We also characterized the temporal relationship between diethylmaleate-induced glutathione depletion and Na + K + ATPase activity. Diethylmaleate (216 mg/kg; i.p.) was given to rats and at various times (0–200 min), after administration the hearts were removed and assayed for glutathione. During the first 30 min after administration glutathione fell from 1.74±0.03 to its lowest value of 0.90±0.04 μmol/g wet weight. It then progressively recovered to within control levels by 150 min after administration. Na + K + ATPase activity paralleled the recovery of glutathione status. In additional studies, the cell-permeant glutathione analogue YM 737 (glutathione isopropyl ester: 1 mmol/kg, i.p.) accelerated the recovery of tissue glutathione and evoked a commensurate and parallel increase in the rate of recovery of Na + K + ATPase activity. Our studies suggest there is a close coupling between tissue glutathione content and Na + K + ATPase activity and that this may be an important factor in ischemia and reperfusion-induced changes in Na + K + ATPase activity.