EFFECT OF MELITTIN ON ELECTROPHYSIOLOGICAL PARAMETERS IN THE FROG CORNEA EPITHELIUM

The effect of melittin on electrophysiological parameters of the bullf rog cornea was studied using an in vitro preparation. Epithelial cells of corneas were impaled with microelectrodes. Experiments were done u nder short-circuit current (I-sc) conditions. Melittin was added in co ncentrations of 10(-5) M to the stromal or 10(-6) M to the tear soluti on. The effects of melittin were as follows: (i) stromal side, a decre ase in I-sc; an increase in the apical membrane fractional resistance, fR(o); no change in the transepithelial conductance, g(t); and a depo larization of the intracellular potential, V-o; (ii) tear side, an ini tial (first 10 min) increase and then a decrease in I-sc; a decrease i n fR(o); an initial (first 10 min) increase with subsequent small decr ease in g(t); and a depolarization of V-o. Changes in tear Na+, but no t in tear K+, with melittin present in tear solution, induced changes in some electrical parameters. The effects on the tear side may be exp lained by opening of nonspecific channels in the apical membrane with some specificity for a Na+ channel. The subsequent effects on the tear and the effects on the stromal side may be explained by an inhibition of the primary transport system, that is, of the Na+/K+-ATPase pump l ocated in the basolateral membrane. In these experiments, there was no evidence of opening of channels in the basolateral membrane.