Amphotericin B-induced sodium transport and water flow across rabbit corneal epithelium

Abstract

We have determined fluid translocation across the cellular layers lining the cornea by measuring changes in corneal transparency. The loss of 1.3 μ1/cm 2 fluid from the stroma causes an increase of +1% in transparency. Amphotericin B ( 2 · 10 -6 M ) when added to the tear side (=mucosal side) of the epithelium causes a rapid increase in potential difference of 12.3 ± 0.7 mV ( mean ± S.E., n=6 ) followed by a slower increase of 18.6 ± 1.5 mV . The electrical resistance is reduced from 3.2 ± 0.3 kΩ · cm 2 to 0.6 ± 0.1 kΩ · cm 2 . The resulting increase in calculated short circuit current is accompanied by a decrease in transparency at a rate of 3.6 ± 1.0% per h , corresponding to an uptake of fluid by the cornea of 4.7 μ l · cm -2 · h -1 . Replacement of the fluid bathing the endothelial side of the cornea, in order to prevent water movement from the aqueous compartment into the stroma, did not significantly alter this uptake of fluid. Thus the epithelial fluid transport which is reported to be normally slightly secretory, becomes absorptive in the presence of amphotericin B. Serosal hypertonicity (20 mM mannitol) increases the water influx into the cornea induced by amphotericin B. These results indicate that amphotericin B induces sodium-selective channels in the epithelium leading to an accumulation of NaCl and water in the stromal layer of the cornea. Ouabain reduces the potential and calculated short circuit current in epithelia pretreated with amphotericin B. Following addition of ouabain, the NaCl and water accumulated in the stroma leak away resulting in a transient increase in transparency. Finally, a model is proposed that includes a stromal compartment involved in fluid transport and that agrees with the results presented here.