Lithium fluxes in human erythrocytes.

The contribution of four transport pathways to Li+ influx and efflux in human erythrocytes was determined quantitatively, using Li+ concentrations comparable to those found in vivo when Li+ is used as treatment for manic-depressive illness. All pathways were measured simultaneously on each subject's blood sample to avoid possible temporal variations in transport parameters. We found that Li+ efflux is 75% via countertransport and 25% via a leak. The bicarbonate-sensitive pathway accounts for 30% of influx while the remaining 70% is via a leak. The Na+-K+ pump makes no significant contribution to Li+ influx or efflux under physiological conditions. Li+ efflux for a given [Li+]i is 3-5 times the Li+ influx for the same [Li+]o. However, due to interindividual variations in Na+-Li+ counter-transport, Li+ efflux but not influx varies considerably among individuals.