Longitudinal endolymph flow associated with acute volume increase in the cochlea.

Salt, A.N. and DeMott, J.E.

Abstract

Endolymph volume disturbances were induced by microinjections of artificial endolymph into the second turn at rates less than 60 nl/min. Induced longitudinal movements and area changes of endolymph were quantified in the basal turn using ionic flow marker techniques. The rate of flow of endolymph measured prior to injection was close to zero, in agreement with prior studies. When artificial endolymph was injected into the second turn, basally-directed flow was observed at a rate which correlated with the injection rate. Under conditions of excess endolymph volume, longitudinal flow out of the cochlea thus provides a significant mechanism contributing to homeostasis. Flow rates measured in the third turn, on the apical side of the injection were far lower and showed characteristics consistent with there being no outlet at the apex. It can be concluded that structures outside the cochlea, such as the endolymphatic sac, play a prominent role in the correction of endolymph volume disturbances. Although the maintenance of endolymph composition is dominated by local, ion transport mechanisms, the capacity of these local mechanisms to maintain normal endolymph volume appears to be extremely limited.

This study was supported by the National Institutes of Health through the National Institute on Deafness and other Communication Disorders, Grant number DC01368

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