Lithium transport across isolated frog skin epithelium

Abstract

Transepithelial Li + influx was studied in the isolated epithelium from abdominal skin of Rana catesbeiana . With Na + -Ringer's as inside medium and Li + -Ringer's as outside medium, the Li + influx across the epithelium was 15.6 μA/cm 2 . This influx was considerably reduced by removal of either Na + or K + from the inside bath or by the addition of ouabain or amiloride. Epithelial K + or Na + concentration was respectively lower in epithelia bathed in K + -free Ringer's or Na + -free Ringer's. In conditions of negligible Na + transport, a 20 mm Li + gradient (out→in) produced across the short-circuited epithelium a Li + influx of 11.8 μA/cm 2 and a mean short-circuit current of 10.2 μA/cm 2 . The same Li + gradient in the opposite direction produced a Li + outflux of only 1.9 μA/cm 2 . With equal Li + concentration (10.3 and 20.6 mm ) on both sides of the epithelium, plus Na + in the inside solution only, a stable Li + -dependent short-circuit current was observed. Net Li + movement (out→in) was also indirectly determined in the presence of an opposing Li + gradient. Although Li + does not substitute for Na + as an activator of the (Na + +K + )-ATPase from frog skin epithelium, Li + influx appears to be related to Na + −K + pump activity. It is proposed that the permeability of the “outer barrier” to Na + and Li + is regulated by the electrical gradient produced by electrogenic Na + −K + pumps located in the membrane of the deeper epithelial cells.