Erythrocyte differentiation of naturally occurring isotopic lithium abundances.

Lithium is effective in the treatment of mania. There are two naturally occurring stable lithium isotopes, Li-7 (92.6%) and Li-6 (7.4%). Usually there is little differentiation between isotopes of an element, but chemical and behavioural data suggest dissimilarities exist between lithium isotopes. Results are now reported indicating that a group of manic patients given lithium chloride were able to differentiate Li-6 from Li-7 at the membrane level. Blood samples were drawn, erythrocytes separated from plasma and the isotopic abundances of Li-6 and Li-7 determined by atomic absorption spectrophotometry. The ratio of abundances of Li-6 in the erythrocyte and plasma was 1.274 indicating the erythrocyte membrane had the in vivo capability of isotope fractionation.