Expression of rat kidney anion exchanger 1 in type A intercalated cells inmetabolic acidosis and alkalosis

By enzyme-linked in situ hybridization (ISH), direct evidence is provided t hat acid-secreting intercalated cells (type A IC) of both the cortical and medullary collecting ducts of the rat kidney selectively express the mRNA o f the kidney splice variant of anion exchanger 1 (kAE1) and no detectable l evels of the erythrocyte AE1 (eAE1) mRNA. Using single-cell quantification by microphotometry of ISH enzyme reaction, medullary type A IC were found t o contain twofold higher kAE1 mRNA levels compared with cortical type A IC. These differences correspond to the higher intensity of immunostaining in medullary versus cortical type A IC. Chronic changes of acid-base status in duced by addition of NH4Cl (acidosis) or NaHCO3 (alkalosis) to the drinking water resulted in up to 35% changes of kAE1 mRNA levels in both cortical a nd medullary type A IC. These experiments provide direct evidence at the ce llular level of kAE1 expression in type AIC and show moderate capacity of t ype A IC to respond to changes of acid-base status by modulation of kAE1 mR NA levels.