Effects of forskolin and 1,9-dideoxy-forskolin on cochlear potentials

Endocochlear potential (EP) and cochlear microphonics (CM) were recorded during the perilymphatic perfusion with forskolin known as an adenylate cyclase stimulant. Forskolin produced a reversible EP elevation in a dose-dependent manner. Perfusion with 1,9-dideoxy-forskolin, an analogue of forskolin that does not stimulate adenylate cyclase, had no effect on EP, whereas perfusions with other agents that raise the cAMP-level (IBMX, a phosphodiesterase inhibitor, and dbcAMP) duplicated the effect of forskolin. The vigorous CM during the EP elevation and the large negative EP induced by anoxia superimposed on the elevated EP indicate that the K+ diffusion potential through the hair cell membrane cannot be altered by forskolin. The results suggest that the adenylate cyclase system in the stria vascularis and/or Reissner's membrane may modulate the generation of EP.