Stimulation of sodium and of chloride transport in epithelia by forskolin.

The diterpene, forskolin, is shown to produce a concentration-dependent, increase in short circuit current in two epithelial preparations, amphibian skin and rat colon. In the amphibian tissue the increase is sensitive to amiloride and due to an increase in electrogenic transepithelial sodium transport towards the serosal side. In the rat colon piretanide attenuated the forskolin effect, suggesting the terpene increases electrogenic transepithelial chloride transport towards the mucosal side. Half-maximal activation of both processes was achieved with concentration of 1-3 microM, similar to those required to activate half-maximally the catalytic subunit of adenylate cyclase.