Regulation of the apical Cl−/HCO 3 − exchanger pendrin in rat cortical collecting duct in metabolic acidosis

Abstract

Pendrin is an apical Cl−/OH−/HCO[Formula: see text] exchanger in β-intercalated cells (β-ICs) of rat and mouse cortical collecting duct (CCD). However, little is known about its regulation in acid-base disorders. Here, we examined the regulation of pendrin in metabolic acidosis, a condition known to decrease HCO[Formula: see text]secretion in CCD. Rats were subjected to NH4Cl loading for 4 days, which resulted in metabolic acidosis. Apical Cl−/HCO[Formula: see text] exchanger activity in β-ICs was determined as amplitude and rate of intracellular pH change when Cl was removed in isolated, microperfused CCDs. Intracellular pH was measured by single-cell digital ratiometric imaging using fluorescent pH-sensitive dye 2′,7′-bis-(3-carboxypropyl)-5-(and-6)-carboxyfluorescein-AM. Pendrin mRNA expression in kidney cortex was examined by Northern blot hybridizations. Expression of pendrin protein was assessed by indirect immunofluorescence. Microperfused CCDs isolated from acidotic rats demonstrated ∼60% reduction in apical Cl−/HCO[Formula: see text] exchanger activity in β-ICs ( P < 0.001 vs. control). Northern blot hybridizations indicated that the mRNA expression of pendrin in kidney cortex decreased by 68% in acidotic animals ( P < 0.02 vs. control). Immunofluorescence labeling demonstrated significant reduction in pendrin expression in CCDs of acidotic rats. We conclude that metabolic acidosis decreases the activity of the apical Cl−/HCO[Formula: see text] exchanger in β-ICs of the rat CCD by reducing the expression of pendrin. Adaptive downregulation of pendrin in metabolic acidosis indicates the important role of this exchanger in acid-base regulation in the CCD.