Regulation of acid secretion in cortical collecting duct : An Effect Mediated by Hensin.

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Metabolic acidosis causes a reversal of polarity of HCO(3)(-) flux in the cortical collecting duct(CCD). In CCDs incubated in vitro in acid media, beta-intercalated (HCO(3)(-)-secreting) cells are remodeled to functionally resemble alpha-intercalated (H(+)-secreting) cells. A similar remodeling of beta-intercalated cells, in which the polarity of H(+) pumps and Cl(-)/HCO(3)(-) exchangers is reversed, occurs in cell culture and requires the deposition of polymerized hensin in the ECM. CCDs maintained 3 h at low pH ex vivo display a reversal of HCO(3)(-) flux that is quantitatively similar to an effect previously observed in acid-treated rabbits in vivo. We followed intracellular pH in the same beta-intercalated cells before and after acid incubation and found that apical Cl/HCO(3) exchange was abolished following acid incubation. Some cells also developed basolateral Cl(-)/HCO(3)(-) exchange, indicating a reversal of intercalated cell polarity. This adaptation required intact microtubules and microfilaments, as well as new protein synthesis, and was associated with decreased size of the apical surface of beta-intercalated cells. Addition of anti-hensin antibodies prevented the acid-induced changes in apical and basolateral Cl(-)/HCO(3)(-) exchange observed in the same cells and the corresponding suppression of HCO(3)(-) secretion. Acid loading also promoted hensin deposition in the ECM underneath adapting beta-intercalated cells. Hence, the adaptive conversion of beta-intercalated cells to alpha-intercalated cells during acid incubation depends upon ECM-associated hensin.