title: 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(3)(-) exchanger in beta-intercalated cells (beta-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(3)(-) secretion in CCD. Rats were subjected to NH(4)Cl loading for 4 days, which resulted in metabolic acidosis. Apical Cl(-)/HCO(3)(-) exchanger activity in beta-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 approximately 60% reduction in apical Cl(-)/HCO(3)(-) exchanger activity in beta-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(3)(-) exchanger in beta-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.
authors.affiliation: Department of Medicine, University of Cincinnati, Ohio 45267-0485, USA.
authors.forename: Snezana
authors.initials: S
authors.lastname: Petrovic
authors.forename: Zhaohui
authors.initials: Z
authors.lastname: Wang
authors.forename: Liyun
authors.initials: L
authors.lastname: Ma
authors.forename: Manoocher
authors.initials: M
authors.lastname: Soleimani
mesh_terms: D000136:Acid-Base Equilibrium / Q000502:physiology; D000138:Acidosis / Q000378:metabolism*; D000595:Amino Acid Sequence; D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism*; D027963:Chloride-Bicarbonate Antiporters / Q000235:genetics* / Q000378:metabolism*; D004232:Diuretics / Q000494:pharmacology; D005260:Female; D005455:Fluorescent Antibody Technique; D015870:Gene Expression / Q000502:physiology; D007672:Kidney Cortex / Q000378:metabolism; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D000076988:Sulfate Transporters
chemical_list: D002352:Carrier Proteins; D027963:Chloride-Bicarbonate Antiporters; D004232:Diuretics; D026901:Membrane Transport Proteins; D012333:RNA, Messenger; C085609:SLC26A4 protein, human; D000076988:Sulfate Transporters; D000643:Ammonium Chloride