Angiotensin II directly stimulates activity and alters the phosphorylation of Na-K-ATPase in rat proximal tubule with a rapid time course

Abstract

We present evidence that Na-K-ATPase in the rat proximal tubule is directly activated by ANG II much faster than previously observed. Specifically, we show that a 2-min exposure to 0.1 and 1 nM ANG II slowed the rate of intracellular sodium accumulation in response to an increase in extracellular sodium added in the presence of gramicidin D. From these data, we show that ANG II directly stimulates Na-K-ATPase activity at rate-limiting concentrations of intracellular sodium. Under these same conditions, exposing proximal tubules to ANG II altered the amount of 32P incorporated into multiple phosphopeptides generated from a tryptic digest of the alpha-subunit of Na-K-ATPase. Na-K-ATPase was isolated from whole cell lysates by means of a ouabain-affinity column and then separated into its individual subunits by SDS-PAGE. Na-K-ATPase bound to the column in its E2 conformation and was eluted by altering its conformation to E1 using Na+ATP. Na-K-ATPase isolated from cells treated with ANG II eluted more easily from the ouabain-affinity column than Na-K-ATPase isolated from control cells, suggesting that ANG II decreased the affinity of Na-K-ATPase for ouabain. Thus ANG II rapidly stimulated the activity of Na-K-ATPase in 2 min or less by a mechanism that could involve changes in phosphorylation and conformation of Na-K-ATPase. We suggest that the physiological role for rapid direct activation of Na-K-ATPase is greater control of intracellular sodium during sodium reabsorption.

Angiotensin II-induced hypertension increases plasma membrane Na pump activity by enhancing Na entry in rat thick ascending limbs

“…There are no previous reports in the literature to our knowledge showing the effects of chronic ANG II infusion on Na pump activity by this segment; however, there is one study showing that at longer infusion times Na pump expression decreases in the ISOM (44). Our results are consistent with studies in the proximal tubule that show that acutely ANG II stimulates Na pump activity (18,66). They are also consistent with studies showing that chronic elevations of ANG II enhance Na pump activity in other tissues (20,26).…”

Alloxan-induced diabetes reduces sarcolemmal Na+-K+ pump function in rabbit ventricular myocytes

“…The [K] pip dependence is consistent with an effect of ANG II to accelerate the backward E 1 ϩ 2K ϩ 3 E 2 (K ϩ ) 2 reaction (5). ANG II increases Na ϩ -K ϩ -ATPase activity and enhances phosphorylation of peptide fragments cleaved from the intact enzyme in rat proximal renal tubule (42). However, the effects of PKCmediated phosphorylation of the Na ϩ -K ϩ pump are varied and tissue specific.…”

Proximal Nephron

“…Many humoral factors, high salt intake, or hormones regulate proximal tubular sodium transport at least in part by altering the expression and activity of Na + -K + -ATPase or by inducing the endocytosis of Na + -K + -ATPase into proximal tubule cells (95; 132; 324). For example, Yingst et al demonstrated that the vasoactive peptide angiotensin II (ANG II) directly stimulates the activity and alters the phosphorylation of Na + -K + -ATPase in rat proximal tubules with a rapid time course (561; 562). Similar effects of ANG II on Na + -K + -ATPase activity were reported in proximal tubule cells or proximal straight tubules in vitro (126; 152).…”