MODULATION OF CARDIAC NA-K+ PUMP CURRENT - ROLE OF PROTEIN AND NONPROTEIN SULFHYDRYL REDOX STATUS()

Oxidant stress alters protein structure and function, possibly through the modification of the redox status of regulatory protein sulfhydryl groups. We used the sulfhydryl-blocking reagent p-chloromercuriphenyl sulfonic acid (pCMPSA), applied selectively and independently to eithe r the intracellular or extracellular environment, to study the relatio nship between blocking protein sulfhydryl groups and Na+-K+ pump curre nt (i(p)). In guinea pig ventricular myocytes voltage clamped at -30 m V, extracellular pCMPSA (50, 100, and 400 mu M) caused a concentration -dependent reduction in holding current. The selective intracellular a dministration of pCMPSA (100 mu M) induced a similar inhibition of i(p ), albeit over a longer time course. The inhibition of i(p) resulting from either the intracellular or extracellular application of pCMPSA ( 100 mu M) was reversed, in part, by the extracellular application of d ithiothreitol (3 mM). An intracellular oxidant stress was also imposed by using diethyl maleate to deplete the intracellular nonprotein sulf hydryl content [represented by reduced glutathione (GSH)]. In myocytes isolated from diethyl maleate-treated guinea pigs (860 mg/kg ip, 30 m in before study), intracellular GSH was depleted by 93% and i(p) was d epressed by 38% at all membrane potentials tested. We propose that Na-K+ pump function may be related to protein and nonprotein sulfhydryl status. Protein sulfhydryl oxidation and glutathione depletion may acc ount, in part, for a depression in Na+-K+ pump activity during reperfu sion-induced oxidant stress.