FAILURE OF FORSKOLIN TO ELEVATE THE ENDOCOCHLEAR POTENTIAL IN KANAMYCIN-POISONED ANIMALS

The effect of forskolin (FSK) on the endocochlear potential (EP), K+ a ctivity (A(K)), Na+ activity (A(Na)) and Cl- activity (A(Cl)) in scala media (SM) was compared between normal and kanamycin (KM)-poisoned gu inea pigs by means of double-barrelled ion-selective microelectrodes. The perfusion of the scala vestibuli (SV) with FSK (200 mu M) produced EP elevation in normal animals whereas FSK failed to do it in KM-pois oned animals. FSK increased A(Cl) of SM with no significant change in A(k), and A(Na) of SM in both groups of animals. Histological examinat ion of KM-poisoned animals showed damaged outer and inner hair cells w ith an intact appearance of the stria vascularis. The mechanism underl ying the failure of FSK to elevate the EP in KM-poisoned animals is di scussed.