The origin of the basal cell potential in frog corneal epithelium.

1. As the micro-electrode penetrated through the epithelial cell membranes of frog cornea, a stepwise increase in the potential reaching a maximum value of - 60 mV (;basal cell potential') was observed. Upon penetrating the stroma, the potential dropped abruptly but remained negative (;stroma potential').2. The basal cell potential was determined as a K(+) or a Cl(-) electrode, but the cell membrane was far more permeable to Cl(-) than to K(+). It was also permeable to Na(+), but to a smaller extent.3. When the product [K](o).[Cl](o) was kept constant, for a tenfold increase in [K](o) the slope of the basal cell potential approached 58 mV at high [K](o). The slope was greater in the excised cornea than in the whole eye.4. The basal cell membrane was more permeable to SCN(-) than to Cl(-). Its selectivity towards cations was in the order K(+) > Rb(+) > Cs(+) > NH(4) (+).5. In Li(+) solution the basal cell membrane in the excised cornea caused a hyperpolarization, followed by a gradual depolarization. In contrast, a slow progressive hyperpolarization occurred in the whole eye.6. Ouabain applied to the epithelial surface of both kinds of preparations did not affect the basal cell potential, but the potential was reduced when applied to the endothelium. MIAA and FDNB also depolarized when applied to both sides of the basal cell.7. With 90 mM-K(+) solution containing Cl(-) or CH(3)SO(4) (-) applied to the epithelial surface, the potential change occurred only in the high K(+) solution with CH(3)SO(4) (-).8. The significance of these results for understanding the role of the epithelial boundary regulating the influence of Na(+), K(+), Cl(-) and drugs is discussed.