Ionic channels in corneal endothelium

Single-channel patch-clamp techniques as well as standard and perforated- patch whole cell voltage-clamp techniques have been applied to the study of ionic channels in the corneal endothelium of several species. These studies have revealed two major K⁺ currents. One is due to an anion- and temperature-stimulated channel that is blocked by Ca⁺ but not by most other K⁺ channel blockers, and the other is similar to the family of A-currents found in excitable cells. The A-current is transient after a depolarizing voltage step and is blocked by both 4-aminopyridine and quinidine. These two currents are probably responsible for setting the -50 to -60 mV resting voltage reported for these cells. A Ca²⁺activated ATP-inhibited nonselective cation channel and a tetrodotoxin-blocked Na⁺ channel are possible Na⁺ inflow pathways, but, given their gating properties, it is not certain that either channel works under physiological conditions. A large- conductance anion channel has also been identified by single-channel patch- clamp techniques. Single corneal endothelial cells have input resistances of 5-10 GΩ and have steady-state K⁺ currents that are ~10 pA at the resting voltage. Pairs or monolayers of cells are electrically coupled and dye coupled through gap junctions.