Properties of single potassium-selective ionic channels from the apical membrane of rabbit corneal endothelium.

The corneal endothelium from several species contains a highly conductive, flickery potassium selective channel in the apical membrane. The channel flicker is not due to blockade. The single channel has an inwardly rectifying current-voltage relationship under symmetrical ionic conditions. Based on reversal potential measurements, it is more than 40:1 selective for potassium over sodium. It also shows subconductance levels. In bathing solutions lacking chloride and bicarbonate, its open probability is less than 0.1 and is quite independent of voltage in the physiological voltage range. Bicarbonate in the bath or DIDs in the pipette increase channel activity. The channel is blocked by external cesium in the 0.5 to 5 mM range. The steepness of the voltage dependence of this blockade is consistent with multiple occupancy.