Responses of the Endolymphatic Sac to Perilymphatic Pressure Manipulations Suggest the Presence of a One-way Valve.

Salt, A.N. and Rask-Andersen, H.

Abstract

It has not been well established what situations result in endolymph movements to or from the endolymphatic sac (ES). In a prior study, we showed with ES recordings that changes of luminal K+, Na+ and endolymphatic sac potential (ESP) could be induced by manipulations of endolymph volume in the cochlea (Salt and DeMott, 2000, Hear. Res. 149, 46). The direction of change was opposite for injections and withdrawals of fluid, suggesting that endolymph movements could occur in either direction. We have now studied the influence of perilymphatic manipulations on K+ and ESP changes in the ES of guinea pigs. Although perilymph withdrawals caused K+ and ESP reductions, the majority of perilymph injections did not induce measurable changes in the ES. Pressure measurements from the ES showed that transmission of labyrinthine pressures to the sac lumen was directionally sensitive, with negative pressures transmitted more effectively than positive ones. These physiologic data suggest that the endolymphatic duct is closed in most animals when pressure in the vestibule is increased. Anatomic study of the region where the endolymphatic duct enters the vestibule shows that the wall of the membranous sinus of the endolymphatic duct could collapse against the bony wall during pressure applications. This would close the entrance to the endolymphatic duct and act as a mechanical one-way valve, restricting flow of endolymph from the saccule to the ES. The endolymphatic sinus could potentially play an important role in detecting and compensating for abnormal endolymph volume states.
 

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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