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.