Effect of substrate-free vascular perfusion upon cochlear potentials and glycogen of the stria vascularis

The effect of vascular perfusion of the anterior inferior cerebellar artery with synthetic blood containing no metabolic substrates upon the endolymphatic potential (EP) and the cochlear microphonics (CM) was determined in the guinea pig. In substrate-free perfusion the potentials were maintained for an average of 84 min. Subsequently, the EP declined at an average rate of 1.4 mV/min until a new steady-state level was temporarily established when the potential had dropped to about 30 mV. The decline of the CM appeared to be accounted for largely by the decline of the EP. During substrate-free perfusion prior to the onset of the decline of the potentials, the level of strial glycogen remained unchanged; glycogen decreased significantly only after the potentials had started to decline. When substrate-free vascular perfusion was accompanied by simultaneous substrate-free perilymphatic perfusion, the potentials started to decline immediately. On the basis of these data, we conclude that strial glycogen plays no role in the prolonged maintenance of the EP during substrate-free perfusion; rather, the potential seems to be maintained by entry of glucose (and presumably other substrates) from perilymph into the stria vascularis.