抄録
Electrogenic Na+-HCO3− cotransporter (NBCe) plays an important role in mediating HCO3− efflux and influx across the basolateral membrane in various HCO3−-transporting epithelia, including kidney proximal tubules and pancreatic ducts. Its activity has been generally assessed by monitoring intracellular pH, Na+ concentration, or membrane potential, but electrophysiological properties of the cotransporter at the native state still remain largely unknown. Using the whole-cell patch clamp technique, we have recently, for the first time, identified and characterized membrane currents attributable to the activity of a NBCe expressed in acutely dissociated acinar cells (BPA cells) from bovine parotid that secretes large volumes of a HCO3−-rich fluid. Under voltage-clamp conditions, the currents were dependent upon extracellular Na+ and HCO3− and DIDS-sensitive. Further analysis of the currents indicated that the stoichiometry of the native cotransporter is most likely to be 2 HCO3− : 1 Na+. We could also demonstrate that BPA cells express transcripts of NBCe1-B (bNBCe1-B) and that recombinant bNBCe1-B currents in HEK293 cells shares common electrophysiological and pharmacological properties with those of the native currents. This study represents an initial attempt to provide electrophysiological characterization of a NBCe expressed in a native HCO3−-secreting exocrine gland. [J Physiol Sci. 2006;56 Suppl:S112]
