The effect of adenylate cyclase stimulation on endocochlear potential in the guinea pig.

Forskolin, a diterpene extracted from Coleus forskohlii, is potentially an important tool for studying the modulation of ionic currents by cAMP because it stimulates adenylate cyclase in a variety of cells. We studied the effect of forskolin on cochlear potentials and found that its perfusion of the scala vestibuli (SV) to a concentration more than 10(-5) M and the scala tympani (ST) to more than 10(-4) M produced a reversible elevation of the endocochlear potential (EP) in a dose-dependent manner. The cochlear microphonics recorded simultaneously with the EP was not depressed during the EP elevation. A large negative EP was induced by anoxia following the SV perfusion with forskolin (2 X 10(-4) M). The results suggest that the EP elevation produced by forskolin does not result from the decrease in the negative component of EP but from the increase in the positive component of EP.