Figure 3

Proposed cell model for P2Y, PKC and PI3-K regulation of ion transport by SCCD epithelium. Na⁺ is absorbed from endolymph by entry into the cytosol across the apical membrane via the epithelial Na⁺ channel (ENaC). Na⁺ is removed from the cytosol across the basolateral membrane by the Na⁺, K⁺-ATPase (Na⁺-pump); K⁺ entering the cell on the Na⁺, K⁺-ATPase recycles across the basolateral membrane via K⁺ channels. Activity of this Na⁺ absorptive mechanism is stimulated by activation of the glucocorticoid receptor (GR), by activity of phosphoinositide-3 kinase (PI3-K) and inhibited by activity of protein kinase C (PKC). Activation of the P2Y2 receptor (P2Y2-R) in the basolateral membrane reduces the barrier to ions of the tight junctions (TJ) and stimulates Cl^- secretion.