Involvement of Cl − transport in forskolin-induced elevation of endocochlear potential

To determine the possible involvement of Cl − transport in the forskolin-induced endocochlear potential (EP) elevation, the effect of forskolin on the EP was examined in Cl −-free artificial perilymph (aPL) as well as in the presence of Cl − channel blockers. The perfusion of scala vestibuli (SV) with forskolin (200 μM) dissolved in Cl −-free aPL failed to produce an EP elevation, while SV perfusion of forskolin dissolved in normal aPL elevated the EP. The application of DPC and IAA-94 (blockers of cAMP-activated Cl − channel) into SV completely suppressed the forskolin-induced EP elevation, while niflumic acid (a Ca 2+-activated Cl − channel blocker) failed to do so. IAA-94 applied into scala tympani (ST) did not suppress this EP elevation. The results suggest that adenylate cyclase may modulate the EP by changing Cl − transport between SV and scala media (SM) across Reissner's membrane.