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This Article Full Text Full Text (PDF) All Versions of this Article: 568/1/181    most recent jphysiol.2005.088633v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Yamaguchi, S. Articles by Ishikawa, T. Search for Related Content PubMed PubMed Citation Articles by Yamaguchi, S. Articles by Ishikawa, T.

¹ Laboratory of Physiology, Department of Biomedical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan

Using patch-clamp and molecular biological techniques, we identified and characterized membrane currents most likely generated by an electrogenic Na⁺–HCO₃^– cotransporter (NBCe) in acutely dissociated bovine parotid acinar (BPA) cells. When BPA cells were dialysed with a N-methyl-D-glucamine (NMDG)-glutamate-rich pipette solution, switching a Na-glutamate-rich, nominally HCO₃^–-free bath solution to the one containing 25 mM HCO₃^–, but not Cl^–, elicited a whole-cell current with a linear current–voltage relation. The HCO₃^– evoked current was abolished by total replacement of extracellular Na⁺ (Na⁺_o) with NMDG or by 0.5 mM 4,4'-diisothiocyanato-stilbene-2,2'-disulfonic acid (DIDS), and was only partially supported by Li⁺_o, but not by K⁺_o, Cs⁺_o, and choline_o. The reversal potential shift of DIDS (0.5 mM)-sensitive current induced by a change of [Na⁺]_o corresponded to an apparent coupling ratio of HCO₃^– to Na⁺ of 2. RT-PCR analysis showed the presence of transcripts of NBCe1-B, but not NBCe1-A in BPA cells. Electrophysiological and pharmacological properties of whole-cell currents recorded from HEK293 cells transfected with the NBCe1-B, which was cloned from BPA cells resembled those of the native currents. Non-invasive measurements of membrane potential changes in the cell-attached patch configuration indicated that an NBCe activity is present in intact unstimulated BPA cells bathed in a 25 mM HCO₃^–-containing solution. Collectively, these results not only suggest that an NBCe is present, functional and may be mediated, at least in part, by NBCe1-B in BPA cells, but also provide the first electrophysiological characterization of transport properties of NBCe expressed in native exocrine glands.

(Received 15 April 2005; accepted after revision 18 July 2005; first published online 21 July 2005)
Corresponding author T. Ishikawa: Laboratory of Physiology, Department of Biomedical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan. Email: torui{at}vetmed.hokudai.ac.jp

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