SV perilymph has a significantly higher potassium level, and slightly lower sodium. Endolymph is a totally unique extracellular fluid, with an ion composition unlike that that found anywhere else in the body. The major cation in endolymph is potassium , and there is virtually no sodium. Because endolymph is so unlike other body fluids, the processes by which it is maintained and regulated cannot be extrapolated from other fluid systems. As shown in the chart above, the total ion content of endolymph is significantly higher than that of perilymph.
Cochlear endolymph is also unique in other respects, as shown in the table below.
It is held at a positive voltage with respect to perilymph, of approximately 85 mV. This is called the endocochlear potential Both the low Ca level and endocochlear potential are extremely important for the cochlea to function normally. Even small changes from the normal state result in a decrease of hearing sensitivity.