Fig. 6

Cell model of H⁺ and K⁺ secretion by strial marginal cells in the cochlea. Transepithelial secretion of K⁺ is mediated by uptake of K⁺ from the basolateral side of the strial marginal cells (SMC) via the Na⁺,K⁺-ATPase and the Na⁺,2Cl⁻,K⁺-cotransporter (NKCC1). The contribution to K⁺ flux by the gastric H⁺,K⁺-ATPase is minimal. K⁺ transport from the cytosol into endolymph is mediated by KCNQ1/KCNE1 K⁺ channels in the apical membrane. Metabolically-generated acid exits the cell via the basolateral gastric H⁺,K⁺-ATPase and the apical Na⁺,H⁺-exchangers. Apical membrane H⁺ exit is increased when the basolateral H⁺,K⁺-ATPase is inhibited and the H⁺ flux re-routed to the apical membrane. Cl⁻ that was taken up into the cytosol via the Na⁺,2Cl⁻,K⁺-cotransporter is recycled across the basolateral membrane via the ClC-K/barttin Cl⁻ channels. Additional putative acid/base transporters, such as basolateral DIDS-sensitive HCO₃ ⁻ efflux via NBCe1, are not shown