Figure 3.
Schematic of the stria vascularis. The stria comprises two cellular layers separated by an intrastrial space. Marginal cells face the endolymph and intermediate/basal cells, interconnected by gap junctions (blue pairs of lines), are exposed to fibrocytes of the strial ligament and perilymph; adjacent cells in each layer are linked by tight junctions (purple). (Note that the orientation is reversed with regard to that shown in Figure 2.) Flow of K+ ions is facilitated by the inwardly-rectifying KCNJ10 K+ channel on intermediate cells and the KCNQ1/KCNE1 K+ channel on the endolymphatic aspect of the marginal cells. Ionic balance is maintained by Na/K ATPase, Na-2Cl-K and Cl transporters. The voltages given (+90, +100, +10 mV) refer to the static potentials of the extracellular spaces with respect to the scala tympani. The endolymphatic potential of +90 mV is attributable to a Nernst K+ equilibrium potential of ~100 mV across the highly K+ selective apical membrane of intermediate cells. The intrastrial space has low K+ due to uptake of the ion by the Na-2Cl-K cotransporter and the Na/K ATPase and K+ is then secreted into endolymph across the K+-selective membrane of marginal cell.