Acid incubation reverses the polarity of intercalated cell transporters, an effect mediated by hensin
George J. Schwartz, Shuichi Tsuruoka, Soundarapandian Vijayakumar, Snezana Petrovic, Ayesa Mian, Qais Al-Awqati
George J. Schwartz, Shuichi Tsuruoka, Soundarapandian Vijayakumar, Snezana Petrovic, Ayesa Mian, Qais Al-Awqati
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Acid incubation reverses the polarity of intercalated cell transporters, an effect mediated by hensin

Abstract

Metabolic acidosis causes a reversal of polarity of HCO3– flux in the cortical collecting duct (CCD). In CCDs incubated in vitro in acid media, β-intercalated (HCO3–-secreting) cells are remodeled to functionally resemble α-intercalated (H+-secreting) cells. A similar remodeling of β-intercalated cells, in which the polarity of H+ pumps and Cl–/HCO3– 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 HCO3– flux that is quantitatively similar to an effect previously observed in acid-treated rabbits in vivo. We followed intracellular pH in the same β-intercalated cells before and after acid incubation and found that apical Cl/HCO3 exchange was abolished following acid incubation. Some cells also developed basolateral Cl–/HCO3– 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 β-intercalated cells. Addition of anti-hensin antibodies prevented the acid-induced changes in apical and basolateral Cl–/HCO3– exchange observed in the same cells and the corresponding suppression of HCO3– secretion. Acid loading also promoted hensin deposition in the ECM underneath adapting β-intercalated cells. Hence, the adaptive conversion of β-intercalated cells to α-intercalated cells during acid incubation depends upon ECM-associated hensin.

Authors

George J. Schwartz, Shuichi Tsuruoka, Soundarapandian Vijayakumar, Snezana Petrovic, Ayesa Mian, Qais Al-Awqati

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Acid incubation converts HCO3– secretion to HCO3– absorption, a process ...
Acid incubation converts HCO3– secretion to HCO3– absorption, a process that is hensin-dependent. Upper panel: five CCDs (control serum, basal, white bars) secrete HCO3–. When Cl– was removed (Cl-free lumen), HCO3– absorption resulted; the difference is the rate of Cl–-dependent HCO3– secretion (HCO3 flux). After 3-hour incubation at pH 6.8 (black bars), net HCO3– absorption was observed (basal). Removal of luminal Cl– caused a small increase in HCO3– absorption (Cl–-free lumen), and the Cl–dependent HCO3– secretion (HCO3 flux) was substantially less than before acid incubation. Middle panel: five CCDs (anti-hensin antiserum) were incubated similarly, except anti-hensin Ab was included in the bath. Anti-hensin antiserum (black bars) blocked half of the acid-induced change in HCO3– transport (basal) but did not change the flux after removal of luminal Cl– (Cl-free lumen), so that the Cl–-dependent rate of HCO3– secretion (HCO3 flux) was only slightly smaller than preincubation values. Lower panel: four CCDs (anti-hensin antiserum + fusion protein) were incubated similarly, except that hensin Ab had been preincubated with the fusion protein that had been used as the immunogen. After acid incubation (black bars), the pattern of net HCO3– transport (basal), HCO3– absorption (Cl-free lumen), and HCO3– secretory flux was similar to that observed in the upper panel for control serum. *Significantly different from preincubation (P < 0.05); **significantly different from incubation in control serum (P < 0.05).