ROLE OF ENDOLYMPHATIC ANION TRANSPORT IN FORSKOLIN-INDUCED CL- ACTIVITY INCREASE OF SCALA MEDIA

To determine the role of anion transport in the forskolin-induced Cl- increase of scala media (SM), effects of forskolin on the EP (endococh lear potential) and Cl- activity (A(Cl)) in SM were examined with doub le-barrelled Cl--selective microelectrodes. The experiments were carri ed out on guinea pig cochleae, using a few anion transport inhibitors: IAA-94 for a Cl- channel blocker, bumetanide (BU) for an Na+/K+/2Cl(- ) cotransport blocker, and SITS and DIDS for Cl-/HCO3- exchange blocke rs. The application of forskolin (200 mu M) into scala vestibuli (SV) caused a 20 mEq increase of endolymphatic A(Cl) and a 15 mV elevation of EP, and IAA-94 with forskolin completely abolished these responses. Although each application of BU, SITS or DIDS did not completely supp ress EP elevation, the concurrent application of these inhibitors comp letely suppressed EP with endolymphatic A(Cl) increase. The results in dicate the involvement of Cl- channels, Na+/K-/2Cl(-) cotransport and Cl-/HCO3- exchange in forskolin-induced increase of A(Cl) and EP. The role of adenylate cyclase activation and Cl- transport in endolymph ho meostasis was discussed.