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Electrophysiological characterization of native Na + –HCO 3 – cotransporter current in bovine parotid acinar cells
Author(s) -
Yamaguchi Souichirou,
Ishikawa Toru
Publication year - 2005
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2005.088633
Subject(s) - dids , cotransporter , chemistry , membrane potential , extracellular , patch clamp , biophysics , pipette , niflumic acid , reversal potential , electrophysiology , intracellular , biochemistry , sodium , membrane , medicine , biology , receptor , organic chemistry
Using patch‐clamp and molecular biological techniques, we identified and characterized membrane currents most likely generated by an electrogenic Na + –HCO 3 − 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 HCO 3 − ‐free bath solution to the one containing 25 m m HCO 3 − , but not Cl − , elicited a whole‐cell current with a linear current–voltage relation. The HCO 3 − evoked current was abolished by total replacement of extracellular Na + (Na + o ) with NMDG or by 0.5 m m 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 m m )‐sensitive current induced by a change of [Na + ] o corresponded to an apparent coupling ratio of HCO 3 − 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 m m HCO 3 − ‐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.