Na+-H+ exchanger in proximal cells isolated from kidney. II. Short-term regulation by glucocorticoids

The purpose of this study was to investigate the acute regulation by glucocorticoid of the Na+-H+ exchanger in isolated renal proximal cells of the rabbit. The changes of intracellular pH (pHi) were determined in a bicarbonate-free buffer by the use of a fluorescent pH probe that may be trapped intracellularly, 2,7-biscarboxyethyl- 5(6)- carboxyfluorescein (BCECF). The activity of the Na+-H+ exchanger was estimated by measuring the Na+-induced H+ efflux in BCECF-loaded cells acid loaded with nigericin in choline medium. The uptake of 1.5 mM 22Na was also studied in Na+-depleted cells. Acute application of dexamethasone increased the activity of the Na+-H+ exchanger. The effect on the kinetics of amiloride-sensitive Na+-H+ exchange indicated that dexamethasone (DEX) increased the activity by increasing the Vmax of the carrier for external sodium and for external H+. The apparent affinity was not modified either for Na+ or for H+. The glucocorticoid action was undetectable after pretreatment of cells with actinomycin D or cycloheximide. Acute glucocorticoid activation of the Na+-H+ exchanger in isolated proximal cells required RNA and protein synthesis and was consistent with an increase in the number of carriers in the membrane