Outwardly rectifying potassium currents in lens epithelial cell membranes.

Isolated epithelial cells from chick, pig, monkey, rabbit, bovine, and human lenses contain K+ channels that often turn on with a delay after a voltage step and have a larger macroscopic conductance for outward currents than for inward currents even with the same K+ concentration on both sides of the membrane. These outward rectifiers are quite diverse between different lens types and more than one kind can be present even within a single lens species. The channels differ substantially in the voltage dependence of their opening, their deactivation time constants, and the time course of their inactivation. Most produce currents of the delayed rectifier type but others show similarities to A-type currents. Because these different channels open at different voltages, inactivate to different degrees and represent different fractions of the total conductance from one lens cell to another, their contribution to the resting voltage is not the same in all cells investigated. These currents are the most frequently occurring in bovine, pig, monkey, and human lens epithelium and also occur commonly in chick lens epithelium. They occur less frequently in rodents.