The in vivo RBC/plasma Li+ ratio is determined by the equilibrium
between Li+ influx (ouabain-sensitive Na+-K+ pump and ouabain- insensitive
leakage pathways) and Li+ efflux (phloretin-sensitive Li+- Na+
counterflow). A study of RBC Li+ transport via these pathways showed that a
deficiency of Li+-Na+ counterflow was responsible for the high in vivo
ratio (1:1) observed in a manic patient. This defect was related to an
alteration in the membrane Na+ exchange system and was under genetic
control. The level of counterflow before lithium therapy was an excellent
predictor (r = .88) of the in vivo Li+ ratio and was deficient in
approximately one-fourth of manic-depressive patients but not in controls,
schizophrenics, or unipolar depressed patients.Abstract Teaser