Endolymph

Endolymph is the fluid contained in the membranous labyrinth of the inner ear.

It is also called Scarpa's fluid, after Antonio Scarpa.

Composition
The main cation of this unique extracellular fluid is potassium, which is secreted from the stria vascularis. The high potassium content of the endolymph means that potassium, not sodium, is carried as the depolarizing electrical current in the hair cells. This is known as the mechano-electric transduction (MET) current.

Endolymph has a high positive charge (from 80-120 mV in the cochlea), mainly due to the presence of positively-charged amino acids. It is mainly this electrical gradient that allows potassium ions to flow into the negatively-charged hair cells during mechanical stimulation of the hair bundle. Because the hair cells are at a negative potential of about -50 mV, the electrical gradient from endolymph to hair cell is on the order of 150 mV, which is the largest electrical potential found in the body.

Pathology
Disruption of the endolymph due to jerky movements (like driving over bumps while riding in a car) can cause motion sickness. A condition where the volume of the endolymph is greatly enlarged is called endolymphatic hydrops and has been linked to Ménière's disease.