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  • Title: A new member of the HCO3(-) transporter superfamily is an apical anion exchanger of beta-intercalated cells in the kidney.
    Author: Tsuganezawa H, Kobayashi K, Iyori M, Araki T, Koizumi A, Watanabe S, Kaneko A, Fukao T, Monkawa T, Yoshida T, Kim DK, Kanai Y, Endou H, Hayashi M, Saruta T.
    Journal: J Biol Chem; 2001 Mar 16; 276(11):8180-9. PubMed ID: 11102437.
    Abstract:
    The kidneys play pivotal roles in acid-base homeostasis, and the acid-secreting (alpha-type) and bicarbonate-secreting (beta-type) intercalated cells in the collecting ducts are major sites for the final modulation of urinary acid secretion. Since the H(+)-ATPase and anion exchanger activities in these two types of intercalated cells exhibit opposite polarities, it has been suggested that the alpha- and beta-intercalated cells are interchangeable via a cell polarity change. Immunohistological studies, however, have failed to confirm that the apical anion exchanger of beta-intercalated cells is the band 3 protein localized to the basolateral membrane of alpha-intercalated cells. In the present study, we show the evidence that a novel member of the anion exchanger and sodium bicarbonate cotransporter superfamily is an apical anion exchanger of beta-intercalated cells. Cloned cDNA from the beta-intercalated cells shows about 30% homology with anion exchanger types 1-3, and functional expression of this protein in COS-7 cells and Xenopus oocytes showed sodium-independent and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid-insensitive anion exchanger activity. Furthermore, immunohistological studies revealed that this novel anion exchanger is present on the apical membrane of beta-intercalated cells, although some beta-intercalated cells were negative for AE4 staining. We conclude that our newly cloned transporter is an apical anion exchanger of the beta-intercalated cells, whereas our data do not exclude the possibility that there may be another form of anion exchanger in these cells.
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