Effect of the Ionophore A23187 on Chloride Transport Across Isolated Frog Cornea

The ionophore A23187 at a concentration of 10(-7) to 10(-5) M stimulated active transport of Cl across the isolated frog cornea. The ionophore had no effect in a Cl-free medium. Both unidirectional Cl fluxes were increased by A23187. The electrical resistance was decreased, and this can be totally accounted for by the increment in passive Cl fluxes. The effect of A23187 on Cl transport and permeability mimicked the effects of cyclic AMP, isoproterenol, and epinephrine. A23187 had no effect when the corneas were fully stimulated by epinephrine or isoproterenol. A23187 produced normal stimulation of the SCC in corneas pretreated with alpha- and beta-adrenergic blockers. The stimulation of the SCC by A23187 was dependent on the presence of Ca in the Ringer solution. Excess Ca (10 mM) resulted in a reduced response. Increasing the Mg concentration in the medium reduced the stimulation of the SCC with Ca concentrations of 0.1-5 mM, but prevented the relative inhibition of 10 mM Ca. Intracellular Ca concentration seemed to regulate Cl permeability of the cornea.