Anion channels in the apical membrane of mammalian corneal epithelium primary cultures.

Chloride ion (Cl-) secretion by the rabbit corneal epithelium involves a catecholamine-stimulated Cl- conductance at the apical membrane, but the characteristics of the ion channel(s) responsible are unknown. A primary cell culture system was developed that induces stratified epithelial differentiation of rat and rabbit corneal epithelial cells, as detected by differential interference contrast light and transmission electron microscopy. In patch clamp studies, gigaOhm seal, were obtained easily during the first 1-4 days in vitro, and patches contained a voltage-dependent outwardly rectifying channel. Single-channel conductance at 24 degrees C was about 10, 29, and 72 pS in symmetric 150 mM NaCl at membrane potentials of -60, 0, and +60 mV, respectively. The current-voltage relationship measured with 75 mM NaCl and sucrose in the bath indicated anion selectivity. Increasing the temperature to 37 degrees C and replacing HEPES buffer with tricine, increased channel conductance and decreased rectification. Characteristics of this channel and a low conductance Cl- channel are compared with those of anion channels of other vertebrate epithelia.