Characteristics of bicarbonate and co2 transport across the skin of
the leopard frog, rana pipiens: effect of pgf2[alpha].
Candia, Oscar A., and Thomas Yorio.
Departments of Ophthalmology, and of Physiology and Biophysics,
Mount Sinai School of Medicine, 100th Street and 5th Avenue, New
York, NY 10029, Department of Pharmacology, University of North Texas
Health Science Center at Fort Worth, 3500 Camp Bowie Boulevard, Fort
Worth, TX 76107
APStracts 3:0333R, 1996.
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 HCO 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 H14CO under a variety of conditions. We report that the
combined CO2 and HCO 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 PGF2[alpha] attenuated the mucosal to serosal flux
and established an apparent secretion of HCO. A model is presented
that depicts twelve vectors or components to the CO2 plus HCO fluxes
in the frog skin. This model can accurately reproduce the
experimental values measured from unidirectional fluxes of CO2 and
HCO under a variety of conditions, and can explain the effects of
PGF2[alpha] on unidirectional 14C-labelled 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 radiolabelled
HCO, may be useful as a means to evaluate the mechanism of action of
hormones and drugs which may regulate acid-base homeostasis by
altering proton and bicarbonate transport processes.
Received 8 March 1996; accepted in final form 30 August 1996.
APS Manuscript Number R144-6.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 September 1996