Distribution of Cl-/HCO3- exchange and intercalated cells in rabbit cortical collecting duct

Abstract

At least two cortical collecting duct (CCD) intercalated cell populations mediate HCO3- secretion and reabsorption. The present study examined the membrane location of intercalated cell Cl-/base exchange activity and the axial distribution of CCD intercalated cells. CCD were studied using in vitro microperfusion in CO2/HCO3(-)-containing solutions; intracellular pH was measured using 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. The A-type intercalated cell (A cell) and B-type intercalated cell (B cell) were identified functionally by the absence and presence of apical Cl-/HCO3- exchange activity, respectively. When a 0 mM Cl-, 0 mM HCO3- luminal solution was used, removal of Cl- from the peritubular solution caused intracellular alkalinization in all B cells. The alkalinization required neither extracellular Na+ nor changes in membrane potential. Peritubular 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) (10(-4) M) inhibited A cell but not B cell basolateral Cl-/base exchange activity. In comparison to studies performed with a 0 mM Cl- 0 mM HCO3- luminal solution, the use of a 0 mM Cl-, 25 mM HCO3- luminal solution inhibited both the identification and the magnitude of B cell basolateral Cl-/base exchange activity. When CCD from the inner and outer cortex were separately studied, only 7% of outer CCD intercalated cells were A cells, whereas 93% were B cells. In contrast, in the inner CCD, 58% of intercalated cells were A cells and 42% were B cells. Under stop-flow conditions, outer CCD alkalinized the luminal fluid, whereas inner CCD acidified the luminal fluid. These results indicate that all CCD intercalated cells possess basolateral Cl-/base exchange activity; however, A cell and B cell basolateral Cl-/base exchange activity differs, at least in terms of sensitivity to DIDS. Furthermore, there is axial heterogeneity in both intercalated cell type and function.

Acid incubation reverses the polarity of intercalated cell transporters, an effect mediated by hensin

“…We had used the pH sensitive dye, BCECF, to identify subtypes of intercalated cells, finding that removal of luminal Clled to alkalinization of β-type intercalated cells (4,5,10,29) since HCO 3 -secretion was inhibited, whereas α-type intercalated cells did not respond because they lacked apical anion exchangers or channels (30). Removal of bath Cl -resulted in alkalinization of α-intercalated cells, because basolateral base exit via the Cl -/HCO 3 -exchanger is inhibited (4, 6, 15).…”

“…Initially, we based our analysis of subtypes of intercalated cells on the presence of PNA, the polarized location of Cl -/HCO 3 -exchange, and the presence of apical endocytosis (4,6). While this provided a simplified distribution of two canonical subtypes, others (9,15,29,38) have shown using a variety of methods that there are more than two subtypes of intercalated cells. In a comprehensive analysis of the pattern of expression of H + -ATPase, Bastani et al (7) concluded that there were six subtypes of intercalated cells and that acidosis shifted the population density toward the α type, while alkalosis shifted it toward the β type.…”

Acid incubation reverses the polarity of intercalated cell transporters, an effect mediated by hensin

“…We had used the pH sensitive dye, BCECF, to identify subtypes of intercalated cells, finding that removal of luminal Clled to alkalinization of β-type intercalated cells (4,5,10,29) since HCO 3 -secretion was inhibited, whereas α-type intercalated cells did not respond because they lacked apical anion exchangers or channels (30). Removal of bath Cl -resulted in alkalinization of α-intercalated cells, because basolateral base exit via the Cl -/HCO 3 -exchanger is inhibited (4, 6, 15).…”

“…Initially, we based our analysis of subtypes of intercalated cells on the presence of PNA, the polarized location of Cl -/HCO 3 -exchange, and the presence of apical endocytosis (4,6). While this provided a simplified distribution of two canonical subtypes, others (9,15,29,38) have shown using a variety of methods that there are more than two subtypes of intercalated cells. In a comprehensive analysis of the pattern of expression of H + -ATPase, Bastani et al (7) concluded that there were six subtypes of intercalated cells and that acidosis shifted the population density toward the α type, while alkalosis shifted it toward the β type.…”

Three N-terminal Variants of the AE2 Cl-/HCO3- Exchanger Are Encoded by mRNAs Transcribed from Alternative Promoters

“…If future experiments prove this hypothesis to be correct, it would not rule out the possibility that the same variant can be sorted to different membranes depending on the cell-type in which it is expressed, but it would provide an explanation of at least one mechanism by which AE2 can be localized to either apical or basolateral membranes. Also, it would implicate AE2b as a possible candidate for the Cl Ϫ /HCO 3 Ϫ exchanger that functions on the basolateral membranes of epithelial cells of renal proximal tubules (36), the thick ascending limb (37), and ␤-intercalated cells of the cortical collecting duct (38).…”