Cardiac Na+/K+ ATPase activity and its relation to myocardial glutathione status: studies in the rat

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, 0.21 +/- 0.02 mumol/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 mumoles/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 mumol/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.