Fig. 3.

Mechanisms of endolymphatic volume marker increase during perilymphatic perfusion with hypertonic media in the in vivo experimental study of Salt and DeMott [78]. Hypertonic (400 mOsm (kg H₂O)⁻¹) perfusion of the perilymphatic scalae (scala vestibuli, SV; scala tympani, ST) in the adult guinea pig cochlea induced osmotic volume changes of the endolymph in the scala media (SM). These volume changes were quantified by Salt and DeMott [78] by measuring the concentration change of the ionic volume marker tetramethylammonium (TMA⁺) after its iontophoretic injection into the endolymph prior to hypertonic perilymphatic perfusion. Salt and DeMott identified two different mechanisms that accounted for the increase in endolymphatic TMA⁺, i.e. shrinkage of the endolymphatic compartment (a and b, area; TMA⁺ increased by 22.1 %) and apically directed longitudinal flow of TMA⁺-loaded endolymph (a and c, movement; TMA⁺ increased by 12.29 %). As the epithelial boundary of the cochlear duct is nearly impermeable to TMA⁺, the induced endolymphatic TMA⁺ increase can be attributed to a loss of endolymph volume that was proportional to the measured TMA⁺ increase. DR, ductus reunions; adapted from [78] with permission from the publisher, Elsevier