AJP - Renal Physiology, Vol 247, Issue 4 602-F606, Copyright © 1984 by American Physiological Society
Inter- and intracompartmental osmotic gradients within the rat cochlea
O. Sterkers, E. Ferrary and C. Amiel
The osmolality and the electrochemical composition of the endolymph, a
potassium-rich positively polarized extracellular fluid in the cochlea, was
studied in the rat. Endolymph of each cochlear turn was hyperosmotic to
perilymph and plasma. Osmolalities (mosmol/kg H2O) were 329 +/- 2.9 (mean
+/- SE) (n = 13) in basal turn endolymph, 322 +/- 2.7 (n = 9) in middle
turn endolymph, 317 +/- 5.2 (n = 3) in apical turn endolymph, 289 +/- 3.1
(n = 14) in perilymph of the scala vestibuli, and 298 +/- 1.8 (n = 7) in
plasma. Moreover, differences in osmolality and electrochemical composition
of endolymph, involving resting potential and K and Cl concentrations, were
observed between the basal and the middle cochlear turns, suggesting the
presence of an electrical and osmotic gradient within endolymph, declining
from the base to the apex of the cochlea. The active potassium transport
into endolymph, located presumably in the stria vascularis, could account
for both the internal and external osmotic gradients.
