Bicarbonate and CO2 transport across the skin of the leopard frog, Rana pipiens: Effect of PGF(2α)

Oscar A. Candia, Thomas Yorio

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The amphibian skin represents an important organ for osmoregulation and, like the mammalian kidney, maintains acid-base balance by secreting protons or base. However, the lack of a reliable and accurate method to measure the contribution of unidirectional fluxes of HCO3 ions to this mechanism has been an obstacle for the determination of the role of bicarbonate in epithelial acid-base homeostasis. Recently, one of us developed a method that allows for the reliable determination of transepithelial fluxes of bicarbonate, and this method was applied to determine unidirectional fluxes of 14CO2 and H14CO3/- under a variety of conditions. We report that the combined CO2 and HCO3/- mucosal-to-serosal flux under 5% CO2 was 40% larger than the opposing flux, giving a net flux in the mucosal-to-serosal direction. This net flux was inhibited by acetazolamide. In CO2-free conditions, there was no detectable net flux; however, acetazolamide and PGF(2α) attenuated the mucosal-to-serosal flux and established an apparent secretion of HCO3/-. A model is presented that depicts twelve vectors or components to the CO2 plus HCO3/- fluxes in the frog skin. This model can accurately reproduce the experimental values measured from unidirectional fluxes of CO2 and HCO3 under a variety of conditions and can explain the effects of PGF(2α) on unidirectional 14C-labeled fluxes as a consequence of inhibition of H+ secretion to the apical bath, similar to what was previously suggested by our laboratory using a different methodological approach. The present method, utilizing radiolabeled HCO3/-, may be useful as a means to evaluate the mechanism of action of hormones and drugs that may regulate acid-base homeostasis by altering proton and bicarbonate transport processes.

Original languageEnglish
Pages (from-to)R640-R647
JournalAmerican Journal of Physiology - Regulatory Integrative and Comparative Physiology
Issue number2 41-2
StatePublished - 1997


  • acetazolamide
  • acid-base balance
  • bicarbonate transport
  • carbonic anhydrase
  • electrolyte transport
  • prostaglandins


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