Studies on the lithium transport across the red cell membrane

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Abstract
Li+ net-transfer across cell membranes was studied on human erythrocytes and ghosts preloaded with 1–2 mM Li+ and incubated in saline media of varying composition at initial thermodynamic equilibrium for Li+. The following results were obtained: Li+ is extruded from glycolyzing erythrocytes against an electrochemical gradient until a steadystate Li+ distribution is established after 24–28 h. The initial rate of Li+ extrusion is not altered by ouabain or by reduction of ATP levels to less than 25% of the normal value. Replacement of external Na+ by K+ or choline+ abolishes the establishment of an electrochemical Li+ gradient. The Li+ distribution ratio Li e + /Li i + increases proportional to the ratio Na e + /Na i + at constant extracellular K+ concentrations. In ghost suspension an uphill Li+ transport is driven by an oppositely directed Na+ gradient. The direction of the Li+ uphill transport can be reversed by reversing the Na+ gradient. From the results it is concluded that the Li+ uphill transport across human red cell membranes is mediated by a Na+-dependent Li+ counter-transport system. This system is not inhibited by ouabain and does not appear to be identical to the Na+−Na+ exchange system described by Garrahan and Glynn [24].