title: Amphotericin B-induced active transport of K+ and the Na+-K+ flux ratio in frog corneal epithelium.
abstract: Transepithelial unidirectional K+ fluxes across the isolated frog cornea were primarily paracellular and proportional to the K+ concentration in the bathing solution (from 2.5 to 25 mM). The net K+ flux was not different from zero. Amphotericin B (10(-5) M) elicited a large and sustained net K+ transport from the stroma- to the tear-side bathing solution of about 10 microA/cm2. Concomitantly, a net Na+ transport occurs in the opposite direction with a short-circuit current from tear to stroma of about 25 microA/cm2. The net K+ transport exhibited saturation, increasing only 35% when the K+ concentration in the bathing solution was augmented five times. Cellular K+ content measured analytically after scraping off the epithelium was reduced by amphotericin B from 0.56 to 0.10 mueq. The amphotericin B-induced K+ transport was inhibited by ouabain and low Na+ (5 mM) in the tear-side solution. Paracellular permeability determined with mannitol or estimated from the tear-to-stroma K+ flux increased four times with amphotericin B. From the net K+ transport and the short-circuit current, the Na+-K+ flux ratio was calculated and found to vary between 2.2 and possibly as high as 5.5 among corneas in the same experimental conditions. The Na+-K+ flux ratio determined in the same cornea decreased as the K+ concentration in the bathing solution increased. Such variability suggests that in corneal epithelial cells the Na+-K+ coupling ratio is sensitive to changes in the electrochemical gradient across the basolateral membrane of the cell.
mesh_terms: D000666:Amphotericin B / Q000494:pharmacology*; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002463:Cell Membrane Permeability / Q000187:drug effects; D003315:Cornea / Q000187:drug effects / Q000378:metabolism*; D004553:Electric Conductivity; D004848:Epithelium / Q000378:metabolism; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D011892:Rana catesbeiana; D012964:Sodium / Q000378:metabolism*
chemical_list: D007473:Ion Channels; D010042:Ouabain; D000666:Amphotericin B; D012964:Sodium; D011188:Potassium