Short-term and long-term stimulation of Na+?H+ exchange in cortical brush-border membranes during compensatory growth of the rat kidney

The effect of unilateral nephrectomy on Na⁺–H⁺ exchange in rat renal cortical brush-border membrane vesicles (BBMV) was studied by the method of acridine orange fluorescence quenching. The exchanger activity in BBMV from remnant kidney increased rapidly by 70–75% within first 30 min following uninephrectomy. Only a slight further increase was found in later stages of renal growth, i.e. 30 min to 7 days following uninephrectomy. The changes in antiporter activity were restricted toV _max, whereas theK _m for Na⁺ was similar in control and compensatory growing kidney. The increase of Na⁺–H⁺ exchange at 15 min was not affected by actinomycin D in vivo, whereas the increase at 48 h was completely abolished indicating that protein synthesis could be involved in the late, but not in the initial stimulation of renal Na⁺–H⁺ exchange. The late, but not the initial stimulations of Na⁺–H⁺ exchange were associated with elevated activities of cortical (Na⁺+K⁺)-ATPase indicating that changes in antiporter activity precede those in the (Na⁺+K⁺)-pump. The early stimulation of Na⁺–H⁺ exchange in BBMV in one kidney was induced also by the occlusion of blood flow through the contralateral kidney for 15 min, without removing it. Thirty min after the occlusion was removed and the reflow established, the Na⁺–H⁺ exchange in BBMV from the intact kidney decreased to the control values. The observed modulations in renal Na⁺–H⁺ exchanger may be regulated by phosphorylation-dephosphorylation events. In support, the concentration of a well known protein kinase C activator, 1,2-diacylglycerol, in the cortical tissue of the remnant kidney increased up to 100% within 5 min following unilateral nephrectomy and preceded the increase in Na⁺–H⁺ exchange. The early stimulation of Na⁺–H⁺ exchange may be a trigger in initiating the kidney growth.