Lithium uptake rate and lithium: lithium exchange rate in human erythrocytes at a nearly pharmacologically normal level monitored by 7Li NMR

7Li NMR was used to follow the rate of uptake of Li+ and Li+:Li+ exchange rates in human erythrocytes at an external lithium concentration of 2 mM, marginally higher than used in therapeutic applications of lithium. The rate of Li+:Li+ exchange is approximately 16 times faster than the rate of Li uptake from the medium. The results are in agreement with lithium-sodium countertransport being the dominant mode for lithium uptake into erythrocytes and for the countertransport system having a greater affinity for Li+ than for Na+.