The mechanism of lithium accumulation in the isolated frog skin epithelium

Summary

The intracellular concentration of Li ([Li]c) of epithelia isolated from frog skins was determined after a one hour exposure to external Na free Choline Ringer containing from 1 to 25 mM of LiCl. In both open and short circuit conditions, [Li]c was found to have values up to ten times that of the outside Li concentration, indicating accumulation of Li in the epithelia. A loss of an approximately equivalent amount of cellular K was associated with this Li accumulation, whereas no significant change in epithelial content of Na was observed. This accumulation of Li is reduced if Na is present together with Li in the outer solution. Preincubation of the epithelia with Amiloride (10⁻⁴ M) suppressed short circuit current and potential difference changes consecutive to externali solutions exposure, prevented Li accumulation and K loss and reduced transepithelial movements of Li. The entry of Li into the cell was speeded up by oxytocin (20 mU/ml). In cyanide (10⁻⁴ M) pretreated epithelia, Li uptake was reduced and accumulation failed to occur. 2,4 dinitrophenol (5×10⁻⁴ M) also lowered the Li uptake. It is concluded that the main mechanism for monovalent cations entry into the epithelium is a process for which Na and Li compete. The existence of an active transport step at the level of the outward facing membrane of the frog skin epithelium is proposed.