Differential regulation of Na+/H+ exchange and H+ -ATPase by pH and HCO3 - in kidney proximal tubules

This study examines the effects of acute in vitro acid-base disorders on Na+/H+ and H+-ATPase transporters in rabbit kidney proximal tubules (PT). PT suspensions were incubated in solutions with varying acid base conditions for 45 min and utilized for brush border membrane (BBM) vesicles preparation. BBM vesicles were studied for Na+/H+ exchange activity (assayed by 22Na+ influx) or abundance (using NHE-3 specific antibody) and H+-ATPase transporter abundance (using antibody against the 31 kDa subunit). The Na+/ H+ exchanger activity increased by 55% in metabolic acidosis (pH 6.5, HCO 3 − 3 mm) and decreased by 41% in metabolic alkalosis (pH 8.0, HCO 3 − 90 mm). The abundance of NHE-3 remained constant in acidic, control, and alkalotic groups. H+-ATPase abundance, however, decreased in metabolic acidosis and increased in metabolic alkalosis by 57% and 42%, respectively. In PT suspensions incubated in isohydric conditions (pH 7.4), Na+/H+ exchanger activity increased by 29% in high HCO 3 − group (HCO 3 − 96 mm) and decreased by 16% in the low HCO 3 − groups (HCO 3 − 7mm. The NHE-3 abundance remained constant in high, normal, and low [HCO 3 − ] tubules. The abundance of H+-ATPase, however, increased by 82% in high [HCO 3 − ] and decreased by 77% in the low [HCO 3 − ] tubules. In PT suspensions incubated in varying pCO2 and constant [HCO 3 − ], Na+/H+ exchanger activity increased by 35% in high pCO2 (20% pCO2, respiratory acidosis) and decreased by 32% in low pCO2 (1.5% pCO2, respiratory alkalosis) tubules. The NHE-3 abundance remained unchanged in high, normal, and low pCO2 tubules. However, the H+-ATPase abundance increased by 74% in high pCO2 and decreased by 69% in low pCO2 tubules.