Candia O A, Yorio T
Department of Ophthalmology, Mount Sinai School of Medicine, New York, New York 10029, USA.
Am J Physiol. 1997 Feb;272(2 Pt 2):R640-7. doi: 10.1152/ajpregu.1997.272.2.R640.
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 (14)CO2 and H(14)CO3 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(2alpha) 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(2alpha) 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.
两栖动物的皮肤是渗透调节的重要器官，与哺乳动物的肾脏一样，通过分泌质子或碱来维持酸碱平衡。然而，缺乏一种可靠且准确的方法来测量HCO3-离子单向通量对这一机制的贡献，一直是确定碳酸氢盐在上皮酸碱稳态中作用的障碍。最近，我们中的一位开发了一种方法，可以可靠地测定碳酸氢盐的跨上皮通量，并将该方法应用于在各种条件下测定(14)CO2和H(14)CO3的单向通量。我们报告，在5% CO2条件下，CO2和HCO3-从黏膜到浆膜的联合通量比反向通量大40%，产生了从黏膜到浆膜方向的净通量。这种净通量受到乙酰唑胺的抑制。在无CO2条件下，没有可检测到的净通量；然而，乙酰唑胺和PGF(2α)减弱了从黏膜到浆膜的通量，并导致了明显的HCO3-分泌。本文提出了一个模型，描述了青蛙皮肤中CO2加HCO3-通量的12个向量或组成部分。该模型可以准确地再现从各种条件下CO2和HCO3-单向通量测量得到的实验值，并可以解释PGF(2α)对单向14C标记通量的影响，这是由于抑制了向顶端浴液的H+分泌，类似于我们实验室之前使用不同方法所提出的。利用放射性标记的HCO3-的本方法，可能作为一种手段来评估激素和药物的作用机制，这些激素和药物可能通过改变质子和碳酸氢盐转运过程来调节酸碱稳态。
