Potassium channels from chick lens epithelium

The technique of patch-voltage clamp has been used to demonstrate several different kinds of K+ channels in the apical membrane of the chick lens epithelium. These include a 200- to 250-ps Ca2+-activated channel, a 200- to 250-ps non-Ca2+-activated channel whose probability of being open increases with hyperpolarization, a 35-ps flickery channel, and a 30-ps inward rectifier, all characterized in symmetrical 150 mM K+. The inward rectifier allows little if any outward current. The probability that the channel is open increases as the membrane patch is depolarized, whereas the mean open and closed times of the channel decrease with depolarization. It is proposed that the rectification is a property of the open channel rather than of its gating. External Cs+ at micromolar concentrations produces a flickery block that increases with hyperpolarization and blocker concentration. The mean open time inside bursts decreases with increasing blocker concentration, whereas the mean intraburst closed time is unaffected. Thus, Cs+ blocks the open channel. The steepness of the voltage dependence of the block suggests that multiple occupancy of the channel is possible.