title: Inhibition of the Na/bicarbonate cotransporter NBCe1-A by diBAC oxonol dyes relative to niflumic acid and a stilbene.
abstract: Na/HCO(3) cotransporters (NBCs) are important regulators of intracellular pH (pH(i) in a variety of organ systems where acid-base status is critical for tissue function. To characterize the pharmacology of NBCs in more detail, we used the two-electrode voltage-clamp technique to examine the effect of previously identified inhibitors of anion exchanger 1 (AE1) on the activity of rat NBCe1-A expressed in Xenopus laevis oocytes. NBC-expressing oocytes voltage-clamped at -60 mV and exposed to a 5% CO(2)/33 mM HCO(3)(-) solution displayed NBC-mediated outward currents that were inhibited by either niflumic acid or one of the two bis-oxonol dyes diBA(3)C4 and diBA(5)C4. NBCe1-A was less sensitive to niflumic acid (apparent K(i) of 100 microM) than 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS, apparent K(i) of 36 microM) but more sensitive to the diBAC dyes (apparent K(i) of approximately 10 microM). Based on current-voltage relationships, the diBAC dyes inhibited HCO(3)(-) -induced NBCe1-mediated inward currents more so than outward currents. NBCe1 sensitivity to the dyes was (1) lower in the presence of 40 microM DIDS, (2) unaffected by changes in external HCO(3)(-) concentration and (3) only modestly higher at an external Na(+) concentration of 5, but not 15 or 33, mM. Therefore, the diBAC dyes compete with DIDS but not appreciably with Na(+) or HCO(3)(-) for binding. The mechanism of diBAC inhibition of NBCe1 appears similar to that previously reported for AE1.
authors.affiliation: Department of Physiology and Biophysics, University of Alabama at Birmingham, 831 MCLM, 1918 University Boulevard, Birmingham, AL 35294-0005, USA.
authors.forename: Xiaofen
authors.initials: X
authors.lastname: Liu
authors.forename: Jennifer B
authors.initials: JB
authors.lastname: Williams
authors.forename: Brandon R
authors.initials: BR
authors.lastname: Sumpter
authors.forename: Mark O
authors.initials: MO
authors.lastname: Bevensee
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D005260:Female; D008564:Membrane Potentials / Q000187:drug effects; D008845:Microinjections; D009544:Niflumic Acid / Q000494:pharmacology*; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D018408:Patch-Clamp Techniques; D018075:RNA, Complementary / Q000008:administration & dosage / Q000235:genetics; D051381:Rats; D027982:Sodium-Bicarbonate Symporters / Q000235:genetics / Q000502:physiology*; D013267:Stilbenes / Q000494:pharmacology*; D014982:Xenopus laevis
chemical_list: D018075:RNA, Complementary; D027982:Sodium-Bicarbonate Symporters; D013267:Stilbenes; D009544:Niflumic Acid; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid