Effect of a chloride channel blocker on bullfrog corneal epithelium.

The effect of the chloride channel blocker, diphenylamine-2-carboxylate (DPC), was investigated on the bullfrog cornea epithelium using microelectrodes. Perfusion of 2 X 10(-4) M DPC on the tear side resulted in a 44% reduction of the corneal transepithelial potential difference (TEP) and a 9% reduction in corneal conductance. The cornea epithelial cells hyperpolarized 7.2 +/- 1.5 mV, and the apical fractional resistance increased 35% (n = 8 tissues). The basolateral potential difference depolarized 5.5 +/- 1.8 mV. The relative apical conductance decreased 29%, whereas relative changes of basolateral membranes increased 56% with prolonged DPC exposure, indicating that the DPC inhibition was acting at the apical cell membrane. DPC-treated corneas could be stimulated with isoproterenol (10(-6) M), indicating that the DPC inhibition could be reversed with the stimulation of chloride conductance. The DPC inhibitory effect was dependent on basolateral chloride. Intracellular chloride activity increases with DPC, indicating that the integrity of the basolateral chloride entry mechanism was not altered. The DPC inhibitory action was due to a reduction in apical chloride conductance.