VOLTAGE-ACTIVATED K-CHANNEL IN LUMINAL MEMBRANE OF MARGINAL CELLS OF STRIA-VASCULARIS DISSECTED FROM GUINEA-PIG

Inward rectifying K channel activity was observed in the luminal membrane of the marginal cell by use of the patch clamp technique. When pipette solution contained 150 mM KCl, the current reversed at 10.2 +/- 8.8 mV (N = 27). The channel current showed multiple subconductance levels and depolarization activated the channel very slowly (order of seconds). Current-voltage relationships in cell-attached mode showed inward rectification. The calculated slope conductance of inward and outward currents were 18 +/- 7 pS and 5.4 +/- 2.0 pS (N = 27), respectively. When pipette solution contained 75 mM NaCl and 75 mM KCI, the current reversed - 7.0 +/- 7.6 mV (N = 6). When pipette solution contained NaCl or Na gluconate, the channel currents were outwardly directed within a range of -60 to 60 mV. These results suggested that the channel is selective to K+. The channel showed immediate run down after excision, and this rundown was not prevented by elimination of cytoplasmic Ca2+. The channel activity was not affected by an increase of intracellular cAMP and cGMP, an application of cytoplasmic catalytic subunit of PKA with ATP. Taking its density into consideration, the channel seems to contribute considerably to the K+ conductance of the luminal membrane of the marginal cell.