Effect of forskolin on conductive anion pathways of toad skin.
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.
Nagel
W
W
Physiologisches Institut, Universität München, Federal Republic of Germany.
Van Driessche
W
W
D000818:Animals; D000838:Anions / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002025:Bufonidae; D002712:Chlorides / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology*; D004553:Electric Conductivity; D009566:Nitrates / Q000378:metabolism / Q000502:physiology; D012879:Skin Physiological Phenomena; D013431:Sulfates / Q000378:metabolism
D000838:Anions; D002712:Chlorides; D009566:Nitrates; D013431:Sulfates; D005576:Colforsin