title: Na-H exchange in rat liver basolateral but not canalicular plasma membrane vesicles.
abstract: Na+-stimulated H+ movement and H+-stimulated Na+ uptake were studied in basolateral (blLPM) and canalicular (cLPM) rat liver membrane vesicles. H+ movement was monitored with the fluorescent amine acridine orange; 22Na uptake was assayed by a rapid Millipore filtration technique. In blLPM, inwardly directed Na+ gradients stimulated H+ efflux and outwardly directed Na+ gradients stimulated proton influx. Outwardly directed proton gradients (pH in 5.9/pH out 7.9) stimulated initial 22Na uptake rates 5- to 10-fold over pH-equilibrated conditions (pH in 7.9/pH out 7.9). Conversely, inwardly directed proton gradients (pH in 7.9/pH out 5.9) inhibited 22Na uptake. pH-dependent 22Na uptake was inhibited by amiloride and harmaline but not by other transport inhibitors, bumetanide, furosemide, 4,4'-diisothiocyano-2,2'-disulfonic acid stilbene, 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid, and acetazolamide. Lithium also inhibited H+-stimulated 22Na uptake. Although a component of pH-stimulated 22Na uptake appeared to be dependent on membrane potential, this electrogenic component was amiloride insensitive. Proton gradient-stimulated 22Na uptake in blLPM was saturable, with a Km of 5.4 mM and a Vmax of 14 nmol . min-1 . mg prot-1. In contrast, in cLPM, no Na+ gradient-stimulated proton movement and no pH-dependent Na+ uptake occurred. These findings establish an electroneutral Na-H antiport in blLPM but not cLPM in rat liver. The polarity of this exchanger supports a model of bile formation that is dependent, in part, on canalicular HCO-3 and/or OH- excretion.
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000165:Acridine Orange / Q000378:metabolism; D000584:Amiloride / Q000378:metabolism; D000641:Ammonia / Q000494:pharmacology; D000818:Animals; D001485:Basement Membrane / Q000378:metabolism; D001693:Biological Transport, Active / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D005374:Filtration; D006863:Hydrogen-Ion Concentration; D008094:Lithium / Q000494:pharmacology; D008099:Liver / Q000648:ultrastructure*; D008297:Male; D008564:Membrane Potentials; D009994:Osmolar Concentration; D011188:Potassium / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D014634:Valinomycin; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D000641:Ammonia; D000584:Amiloride; D008094:Lithium; D012964:Sodium; D000165:Acridine Orange; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D011188:Potassium