Chemical modification of the Na+/H+ exchanger of thymic lymphocytes. Inhibition by N-ethylmaleimide.
A Na+/H+ exchanger is involved in the regulation of cytoplasmic pH and cellular volume in a variety of cells. Little is known about the molecular nature of this exchanger. The purpose of this study was to survey a variety of group-specific covalent reagents as potential inhibitors of the exchanger. Na+/H+ countertransport activity was assayed as the amiloride-sensitive rate of Na+-induced alkalinization in acid-loaded lymphocytes, or as the rate of swelling in cells suspended in sodium propionate medium. Activity was not affected by proteinases or by carboxyl-group and amino-group specific reagents. A significant inhibition was produced by diethylpyrocarbonate, a histidine-specific reagent and by N-ethylmaleimide, a sulfhydryl group reagent. A similarly reactive but nonpermeating sulfhydryl agent, glutathione-maleimide, failed to inhibit Na+-H+ exchange. Moreover, the reaction with N-ethylmaleimide was sensitive to changes in the cytoplasmic pH. The data suggest that the chemically reactive groups of the Na+/H+ exchanger of lymphocytes have limited exposure to the extracellular medium but that an internally located sulfhydryl group is critical for the cation-exchange activity.
Grinstein
S
S
Cohen
S
S
Rothstein
A
A
D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D004047:Diethyl Pyrocarbonate / Q000494:pharmacology; D005033:Ethylmaleimide / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D017923:Sodium-Hydrogen Exchangers; D013601:T-Lymphocytes / Q000187:drug effects / Q000378:metabolism*
D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D004047:Diethyl Pyrocarbonate; D005033:Ethylmaleimide