Intracellular pH-regulating ion transport mechanisms in parietal cell basolateral membrane vesicles.
Na(+)-H+ and Cl(-)-base exchangers on the parietal cell have been demonstrated by several authors. Controversy exists concerning a basolateral Na(+)-HCO3- cotransporter in the parietal cell. To clarify this issue, we prepared highly enriched basolateral membrane (BLM) and apical-tubulovesicular membrane (to serve as negative controls) vesicles from rabbit fundic mucosa. Na(+)-H+ exchange was demonstrated by measuring pH gradient-driven amiloride-sensitive 22Na+ uptake and Na+ gradient-driven proton uptake into voltage-clamped BLM but not into apical-tubulovesicular vesicles. Anion exchange was demonstrated by measuring 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS)-inhibitable influx of 36Cl- into Cl(-)- or HCO3(-)-loaded voltage-clamped BLM vesicles. Na(+)-HCO3- cotransport was assessed by comparing HCO3(-)-driven 22Na uptake with uptake driven by an identical pH gradient. No significant difference was found between 22Na uptake in the presence and absence of HCO3-; 1 mM amiloride inhibited 22Na uptake > 90% in both conditions, whereas 2 mM DIDS had no effect. In BLM vesicles prepared from rabbit renal cortex, however, a HCO3- gradient stimulated 22Na uptake much more than an equivalent pH gradient, and DIDS inhibited this HCO3- gradient-driven 22Na uptake. This indicates that our experimental setup was suitable to detect a Na(+)-HCO3- cotransporter if present. Our data suggest that the parietal cell BLM contains Na(+)-H+ exchangers and Cl(-)-HCO3- exchangers but no Na(+)-HCO3- cotransporter.
Lamprecht
G
G
II. Department of Medicine, Technische Universität München, Germany.
Seidler
U
U
Classen
M
M
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D015415:Biomarkers / Q000032:analysis; D002352:Carrier Proteins / Q000378:metabolism; D002458:Cell Fractionation / Q000379:methods; D002462:Cell Membrane / Q000378:metabolism* / Q000648:ultrastructure; D002499:Centrifugation, Density Gradient / Q000379:methods; D002712:Chlorides / Q000378:metabolism; D017506:H(+)-K(+)-Exchanging ATPase / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008297:Male; D009245:NADH Dehydrogenase / Q000032:analysis; D010295:Parietal Cells, Gastric / Q000378:metabolism* / Q000648:ultrastructure; D011817:Rabbits; D012964:Sodium / Q000378:metabolism; D027982:Sodium-Bicarbonate Symporters; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000032:analysis; D013385:Succinate Dehydrogenase / Q000032:analysis
D001639:Bicarbonates; D015415:Biomarkers; D002352:Carrier Proteins; D002712:Chlorides; D027982:Sodium-Bicarbonate Symporters; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride; D012964:Sodium; D013385:Succinate Dehydrogenase; D009245:NADH Dehydrogenase; D017506:H(+)-K(+)-Exchanging ATPase; D000254:Sodium-Potassium-Exchanging ATPase; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid