Coupling of lithium to sodium transport in human red cells

Abstract

THE administration of lithium salts is often used in the treatment of affective psychoses¹. Mendels et al.^2–4 and others⁵ have measured the concentrations of lithium in blood plasma and red cells of patients and normal individuals receiving such salts. They have argued that the lithium concentrations in red cells can be correlated with the clinical status of these people⁴ and, therefore, can possibly be related to the pathogenesis of the mental disorders. They found that the concentration of lithium in red cell water is about one-third of that in the blood plasma during chronic administration of LiCl (ref. 4). This fact is surprising since it would suggest that Li⁺ is actively transported by the red cell membrane. The steady-state value of the ratio of internal to external concentration for a monovalent cation which is not actively transported should be about 1.2 (ref. 6). Previous observations in red cells⁷ and squid axons⁸ suggested that Li⁺ is not transported by the Na–K pump. Furthermore, the net efflux of Li⁺ into Li⁺-free medium was unaffected by the presence of ouabain⁴. The experiments described here were designed to clarify the mechanisms of this seemingly ouabain-insensitive ‘active’ transport of lithium ions in human red cells.