Electrochemical profiles for monovalent ions in the stria vascularis: cellular model of ion transport mechanisms.

The electrochemical profiles for K+, Na+, and Cl- ions in tissues of the lateral wall of the cochlea in the chinchilla were measured using an ion-selective microelectrode. Based upon the changes of the d.c. resting potential and ion composition, five distinct compartments were identified in the lateral wall. The first compartment, corresponding to the spiral ligament, showed an ionic composition similar to perilymph. The second, corresponding to the basal cell layer of the stria vascularis, showed a characteristic recording of the ion-sensitive barrel: a spike-like change of the ion concentration (K+: 100.1 +/- 16.8 mM, Na+: 33.9 +/- 20.2 mM, Cl-: 70.2 +/- 9.4 mM). The third compartment, corresponding to the extracellular space of the stria vascularis, showed a higher d.c. potential (60.4 +/- 9.5 mV) than that of the second region, with a low K+ concentration (22.1 +/- 14.9 mM) and a high Na+ (78.3 +/- 5.7 mV) than the fifth compartment, corresponding to the scala media (78.1 +/- 4.1 mV), and K+ and Na+ concentrations similar to those of endolymph, while the Cl- concentration in the fourth compartment (117.6 +/- 21.5 mM) was lower than that of endolymph (143.3 +/- 13.9 mM). A thermodynamic study of electrochemical potential gradients suggests the possibility that the Na-K pump and Na-K-2Cl cotransport exist at the basolateral membrane of the marginal cells.