Lithium transport across isolated frog skin epithelium |
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Authors: | Peter S. Reinach Oscar A. Candia George J. Siegel |
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Affiliation: | (1) Department of Ophthalmology, Mount Sinai School of Medicine of the City University of New York, Fifth Avenue and 100th Street, 10029 New York, New York;(2) Department of Neurology, University of Michigan Medical Center, 48104 Ann Arbor, Michigan |
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Abstract: | Summary Transepithelial Li+ influx was studied in the isolated epithelium from abdominal skin ofRana catesbeiana. With Na+-Ringer's as inside medium and Li+-Ringer's as outside medium, the Li+ influx across the epithelium was 15.6 A/cm2. 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 20mm Li+ gradient (outin) produced across the short-circuited epithelium a Li+ influx of 11.8 A/cm2 and a mean short-circuit current of 10.2 A/cm2. The same Li+ gradient in the opposite direction produced a Li+ outflux of only 1.9 A/cm2. With equal Li+ concentration (10.3 and 20.6mm) 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 (outin) 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. |
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