AJP - Cell Physiology, Vol 263, Issue 1 C166-C171, Copyright © 1992 by American Physiological Society
Effect of forskolin on conductive anion pathways of toad skin
W. Nagel and W. Van Driessche
Physiologisches Institut, Universitat Munchen, Federal Republic of Germany.
The effect of the diterpene, forskolin, on pathways for conductive Cl-
transport was analyzed using isolated skins of Bufo viridis. Forskolin did
not stimulate the voltage-activated Cl- movement from mucosa to serosa; the
Lorentzian component in the power density spectrum, which was present at
serosa positive clamp potentials under control conditions, decreased
significantly. The observation that stimulation of cytosolic adenosine
3'-5'-cyclic monophosphate (cAMP) by forskolin has no effect on the
voltage-activated Cl- transport argues against control of this pathway by
cAMP. Our data further demonstrate that the forskolin-activated Cl-
conductive pathway is also permeable for NO3-. This pathway was studied in
absence of mucosal Cl-, which eliminates Cl- movement through the
voltage-activated pathway. With SO4(2-) and Cl- on the mucosal and serosal
sides, respectively, this forskolin-induced pathway displayed a linear
current-voltage relationship. The associated Lorentzians increased at
serosa negative clamp potentials. Transepithelial current and plateau value
of the Lorentzian were related by a quadratic function, which suggests
voltage-independence of number and open-close probability of these
conductance sites. Morphological sites for voltage-activated and
forskolin-induced conductive Cl- transport remain to be identified.
