Phorbol ester-induced alkalinization of canine renal proximal tubular cells

To determine whether exposure of renal proximal tubular cells to tumor-promoting phorbol esters results in intracellular alkalinization, we incubated suspensions of proximal tubular segments isolated from dog kidney with these compounds. Changes in intracellular pH were detected by measurements of the distribution of [14C]5,5-dimethoxazolidine-2-4-dione (DMO). Incubations of segments with 10(-6) M of the tumor-promoting phorbol esters phorbol-12,13-dibutyrate or 12-O-tetradecanoylphorbol-13-acetate (TPA), under conditions such that extracellular [Na+] greater than intracellular [Na+], effected intracellular alkalinization detectable within 1-2 min. Incubation with the inactive phorbol ester 4 alpha-phorbol did not. Incubation with as little as 10(-10) M phorbol-12,13-dibutyrate effected intracellular alkalinization. Incubation with 10(-12) M phorbol-12,13-dibutyrate did not. Alkalinization was not observed under conditions such that extracellular [Na+] = intracellular [Na+]. Alkalinization could be prevented by inclusion of 10(-3) M amiloride in incubations. Our findings are consistent with an action of tumor-promoting phorbol esters to stimulate Na+-H+ exchange across the plasma membrane of the renal proximal tubular cell. It is possible that the stimulation reflects a mechanism by which hormones and/or growth factors exert actions in proximal tubule.