Forskolin-induced HCO3- current across apical membrane of the frog corneal epithelium

O. A. Candia

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Forskolin (and other Cl- secretagogues) does not affect the very small Na+-originated short-circuit current (I(sc)) across frog corneal epithelium bathed in Cl- free solutions. However, forskolin in combination with increased PCO2 bubbling of the solutions (5-20% CO2) stimulated I(sc) proportionally to PCO2 to a maximum of ~8 μA/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 I(sc) 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 I(sc) across the basolateral membrane can be accounted for by the Na+ pump current plus K+ movement from cell to bath. Methazolamide also inhibited I(sc). Current across the apical membrane cannot be attributed to an electronegative Na+-HCO3- symport given the insensitivity of I(sc) to a disulfonic stilbene and the fact that stroma-to-tear Na+ fluxes did not increase on stimulation of I(sc). 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 protein, a reduction in the apical-to-basolateral resistance ratio, and a decrease in transepithelial resistance. The results suggest that forskolin induces a conductance across the apical membrane to intracellularly accumulate HCO3-, the efflux of which produced, with a K+ current across the basolateral membrane, the observed I(sc).

Original languageEnglish
Pages (from-to)C215-C223
JournalAmerican Journal of Physiology - Cell Physiology
Issue number2 28-3
StatePublished - 1990


  • Anion channel
  • Bicarbonate permeability
  • Chloride secretagogues
  • Methazolamide
  • Microelectrode study
  • Quinidine
  • Tryptamine


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