Na+,K(+)-ATPase activity in the cochlear lateral wall of the gerbil

We examined Na+,K(+)-ATPase activity in four regions of the gerbil cochlear lateral wall by measuring intracellular Na+ concentration ([Na+]i). The application of 1 mM ouabain and removal of external K+ caused a most striking increase in [Na+]i of the suprastrial fibrocytes, followed by the stria vascularis and the type II fibrocytes, but no detectable response in the type I fibrocytes. These results may imply the potency of the Na+,K(+)-ATPase activity. The high values of the resting [Na+]i in these cells under perilymph-like solution returned to the [Na+]i within physiological values after exposure to low-Na+ conditions similar to endolymph. Our results are interpreted in the light of recent morphological findings with regard to the roles in the secretion of K+ into endolymph of several cell types within the lateral wall.