Single potassium channels in corneal epithelium.

The basal cell layers of the rabbit and human corneal epithelia contain a frequently occurring ionic channel whose unitary currents can be recorded in cell-attached or excised membrane patches by use of a patch voltage clamp. The channel is highly conductive (165 pS in 150 mM K+ salts) and is very selective for K+ over Na+ (PK/PNa greater than 40:1). Its open probability is increased by the application of suction to the recording pipette although its gating is less sensitive to suction than that of many other "stretch-activated" channels reported. The current through the channel is a saturating function of the K+ concentration in the bathing solutions with half saturation occurring at 480 mM and a single-channel current at saturation (imax) of 31 pA. In the absence of applied suction, the open probability is extremely variable from patch to patch and shows little voltage dependence over the physiologic voltage range. The channel also gates frequently to several subconductance levels. It is blocked by external Cs+ and Ba+2 in the 0.1-10 mM range but not by most other K+ channel blockers. It is also partially blocked by Ca+2 at both its internal and external surfaces. Because of its novel properties (stretch activation and large conductance), it can be used to measure the input resistance and total capacitance of single dissociated cells.