Failure of forskolin to elevate the endocochlear potential in experimental endolymphatic hydrops of the guinea pig

The effect of forskolin (FSK) on the endocochlear potential (EP) in scala media (SM) was examined in experimental endolymphatic hydrops of the guinea pig. Two weeks after obliteration of the endolymphatic sac the EP of hydroptic ears and that of the contralateral control ears were measured by means of microelectrodes. The perfusion of scala vestibuli (SV) with FSK (200 microM) produced EP elevation in the contralateral control ears but failed to do so in the experimental hydroptic ears. Histological examination of experimental endolymphatic hydrops showed mild hydrops with intact appearance of outer and inner hair cells, and the stria vascularis. The mechanism underlying the failure of FSK to elevate the EP in experimental endolymphatic hydrops is discussed.