Forskolin-induced HCO3- current across apical membrane of the frog corneal epithelium.
Forskolin (and other Cl- secretagogues) does not affect the very small Na(+)-originated short-circuit current (Isc) across frog corneal epithelium bathed in Cl- free solutions. However, forskolin in combination with increased PCO2 bubbling of the solutions (5-20% CO2) stimulated Isc proportionally to PCO2 to a maximum of approximately 8 microA/cm2. This current could be eliminated and reinstated by sequentially changing the gas composition of the bubbling to 100% air and 20% CO2-80% air. The same effects were observed when PCO2 changes were limited to the apical-side solution. Stroma-to-tear HCO3- movement was deemed unlikely, since the increase in Isc was observed with a HCO3(-)-free solution on the stromal side and CO2 gassing limited to the tear side. From the effects of ouabain and tryptamine, at least 80% of the Isc across the basolateral membrane can be accounted for by the Na+ pump current plus K+ movement from cell to bath. Methazolamide also inhibited Isc. Current across the apical membrane cannot be attributed to an electronegative Na(+)-HCO3- symport given the insensitivity of Isc to a disulfonic stilbene and the fact that stroma-to-tear Na+ fluxes did not increase on stimulation of Isc. The tear-to-stroma Na+ flux also remained unaltered, negating an increased apical bath-to-cell Na+ flow. The forskolin-20% CO2 manipulation produced a depolarization of the intracellular potential, a reduction in the apical-to-basolateral resistance ratio, and a decrease in transepithelial resistance.(ABSTRACT TRUNCATED AT 250 WORDS)
Candia
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Department of Ophthalmology, Mount Sinai School of Medicine, New York, New York 10029.
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D002245:Carbon Dioxide / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D005576:Colforsin / Q000494:pharmacology*; D003315:Cornea / Q000502:physiology*; D004553:Electric Conductivity; D004594:Electrophysiology / Q000379:methods; D004848:Epithelium / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D008704:Methazolamide / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D010313:Partial Pressure; D011802:Quinidine / Q000494:pharmacology; D011892:Rana catesbeiana; D014363:Tryptamines / Q000494:pharmacology
D001639:Bicarbonates; D014363:Tryptamines; D002245:Carbon Dioxide; D005576:Colforsin; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; C030820:tryptamine; D010042:Ouabain; D011802:Quinidine; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D008704:Methazolamide