Protein kinase C activates the renal apical membrane Na+/H+ exchanger.
Studies were performed on purified brush-border membranes from the kidney of the rabbit to examine the relation between protein kinase C and the Na+/H+ exchanger in these membranes. The brush-border membranes were transiently opened by exposure to hypotonic media and the membrane proteins phosphorylated by exposure to ATP and phorbol esters or partially purified protein kinase C. The membranes were resealed and the intravesicular space acidified by incubation in a sodium-free isotonic solution (pH 5.5). The rate of uptake of 1 mM 22Na+ (pH 7.5), with and without amiloride (1 mM), was assayed and the proton gradient-stimulated, amiloride-inhibitable component of 22Na+ taken as a measure of the activity of the Na+/H+ exchanger. 12-0-tetradecanoyl phorbol-13-acetate (TPA) increased the amiloride-sensitive component of 22Na+ uptake. TPA did not affect the amiloride-insensitive component of 22Na+ uptake or the equilibrium concentration of sodium. TPA also did not affect the rate of dissipation of the proton gradient in the absence of sodium or the rate of sodium-dependent or -independent uptake of D-glucose. Other "active" phorbol esters stimulated the rate of Na+/H+ exchange, but phorbol esters of the 4 alpha configuration did not. Incubation of the opened membranes in partially purified protein kinase C increased the rate of proton gradient-stimulated, amiloride-inhibitable sodium uptake. The stimulatory effect of TPA and protein kinase C was not additive. In the absence of ATP, neither TPA nor protein kinase C affected Na+/H+ exchange transport. To determine the membrane-bound protein substrates, parallel experiments were conducted with gamma-[32P] ATP in the phosphorylating solutions.(ABSTRACT TRUNCATED AT 250 WORDS)
Weinman, EJ; Shenolikar, S
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