Ion channels in basolateral membrane of marginal cells dissociated from gerbil stria vascularis

The basolateral membrane of isolated strial marginal cells has been probed for conductive pathways by the patch-clamp technique. Two types of voltage-insensitive channels were identified in both cell-attached and excised patches. Of these, frequently (69% of excised patches) observed was a Ca²⁺-activated nonselective cation channel having a unit conductance of 24.9 ± 0.5 pS (N = 16). Other characteristics of this type in excised patches include: 1) linear I-V relations with 150 mM K⁺ (pipette)/150 mM Na⁺ (bath), 2) a permeability sequence of NH₄⁺> Na⁺ = K⁺ = Rb⁺>Li⁺, 3) a flickering block by quinine or quinidine (both 1 mM), and 4) a dose dependent block of its activity by ADP or ATP (IC_50,ATP/IC_50,ADP = 20-35), both from the cytosolic side. Channels with similar characteristics were found in the apical membrane of the same cell; however, the basolateral channels were 2-4 times more densely distributed than the apical counterparts. Also frequently (57%) detected was a Cl^- channel of 80.0 ± 0.5 pS (N = 6), whose activity was Ca²⁺ independent. Additionally, this Cl^- channel had: 1) linear I-V relations with symmetric Cl^-, 2) a permeability sequence of Cl^->Br^->I^-≥NO₃^-≥gluconate^-, and 3) a complete and reversible block by 1 mM diphenylamine-2-carboxylate. In contrast to the apical Cl^- channels, the basolateral ones had a much higher density (57% vs. <1%) as well as a higher unit conductance (80 pS vs. 50 pS) than the apical counterpart. The relative abundance of these two types as the major conductive pathways for Na⁺, K⁺, and Cl^- in the basolateral region must be taken into account when addressing the role of strial marginal cells in generating the positive endocochlear potential. The Cl^- channel may facilitate Cl^- distribution across the basolateral membrane.