Voltage-dependent K Channels in Supporting Cells Isolated from Guinea Pig Cochlea
The cochlea hair cells of the mammalian inner ear are held mechanically by a surrounding network of various supporting cells in the organ of Corti located on the basilar membrane. Recently, it has been suggested that these supporting cells have both mechanical and functional connections with sensory hair cells. In this study, Deiters' cells (DCs) and Hensen's cells (HEs) were freshly isolated from the guineapig cochlea, and voltage-dependent outward currents (VDOCs) in both DCs and HEs were measured with conventional whole-cell patch recording techniques. The results obtained were as follows. 1) The whole-cell currents in both cells were VDOCs, which were evoked at about - 20 mV with depolarizing pulses, and were suppressed completely by intracellular Cs+. The current-voltage curve in DCs had a plateau phase at high depolarizing voltages. However, in a Ca-free extracellular solution, this plateau phase disappeared and the current-voltage curve showed a straight line with depolarizing voltages. 2) In an extracellular solution containing lOmM TEA, the VDOCs in both DCs and HEs were suppressed by about 80% of the control K currents. Therefore, the main currents in both cells were rectifying K currents. 3) An intracellular solution containing lOmM 4 - AP suppressed voltage-dependent outward K (VDO-K) currents in both cells. The slow components of these VDO-K currents in HEs were suppressed by more than 90% of the control currents, whereas those in DCs were suppressed by about 40% of the control currents with depolarizing voltages. But these 4-AP-resistant components were disappeared completely with an extracellular solution containing lOmM TEA. From these results, it was concluded that VDO-rectifying K currents were the main currents in the supporting cells, and that DCs also have Ca-activated K currents, which were evoked at high depolarizing voltages.
