The gamma subunit modulates Na+ and K+ affinity of the renal Na,K-ATPase

The Na+,K+F-ATPase catalyzes the active transport of ions. It has two neces sary subunits, alpha and beta, but in kidney it is also associated with a 7 .4-kDa protein, the gamma subunit. Stable transfection was used to determin e the effect of gamma on Na,K-ATPase properties. When isolated from either kidney or transfected cells, alpha beta gamma had lower affinities for both Na+ and K-_ than alpha beta. A post-translational modification of gamma se lectively eliminated the effect on Naf affinity, suggesting three configura tions (alpha beta, alpha beta gamma, and alpha beta gamma*) conferring diff erent stable properties to Na,H-ATPase, In the nephron, segment-specific di fferences in Na+ affinity have been reported that cannot be explained by th e known alpha and beta subunit isoforms of Na,K-ATPase, Immunofluorescence was used to detect gamma in rat renal cortex. Cortical ascending limb and s ame cortical collecting tubules lacked gamma, correlating with higher Na+ a ffinities in those segments reported in the literature. Selective expressio n in different segments of the nephron is consistent with a modulatory role for the gamma subunit in renal physiology.