title: Na+/HCO3-co-transport in basolateral membrane vesicles isolated from rabbit renal cortex.
abstract: Recent studies suggest that the major pathway for exit of HCO3- across the basolateral membrane of the proximal tubule cell is electrogenic Na+/HCO3- co-transport. We therefore evaluated the possible presence of Na+/HCO3- co-transport in basolateral membrane vesicles isolated from the rabbit renal cortex. Imposing an inward HCO3- gradient induced the transient uphill accumulation of Na+, and imposing an outward Na+ gradient caused HCO3- -dependent generation of an inside-acid pH gradient as monitored by quenching of acridine orange fluorescence, findings consistent with the presence of Na+/HCO3- co-transport. In the absence of other driving forces, generating an inside-positive membrane potential by imposing an inward K+ gradient in the presence of valinomycin caused net Na+ uptake via a HCO3- -dependent pathway, indicating that Na+/HCO3- co-transport is electrogenic and associated with a flow of negative charge. Imposing transmembrane Cl- gradients did not appreciably affect HCO3- gradient-stimulated Na+ influx, suggesting that Na+/HCO3- co-transport is not Cl- -dependent. The rate of HCO3- gradient-stimulated Na+ influx was a simple, saturable function of the Na+ concentration (Km = 9.7 mM, Vmax = 160 nmol/min/mg of protein), was inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (I50 = 100 microM), but was inhibited less than 10% by up to 1 mM amiloride. We could not demonstrate a HCO3- -dependent or 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid-sensitive component of Na+ influx in microvillus membrane vesicles. This study thus indicates the presence of a transport system mediating electrogenic Na+/HCO3- co-transport in basolateral, but not luminal, membrane vesicles isolated from the rabbit renal cortex. Analogous to the use of renal microvillus membrane vesicles to study Na+/H+ exchange, renal basolateral membrane vesicles may be a useful model system for examining the kinetics and possible regulation of Na+/HCO3- co-transport.
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism* / Q000494:pharmacology; D001692:Biological Transport; D002458:Cell Fractionation; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D002712:Chlorides / Q000494:pharmacology; D007672:Kidney Cortex / Q000378:metabolism*; D007700:Kinetics; D008954:Models, Biological; D011817:Rabbits; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D017693:Sodium Bicarbonate
chemical_list: D001639:Bicarbonates; D002712:Chlorides; D000584:Amiloride; D017693:Sodium Bicarbonate; D012964:Sodium