Kinetics of lithium efflux through the (Na,K)-pump of human erythrocytes

Evidence from the kinetics of transport supports the hypothesis that cellular Li, Li_c, interacts with the internal aspect of the (Na,K)-pump as a congener of Na, Li_c and Na_c compete for the same sites on the internal aspect of the pump. Li_c promotes Na-activated K influx and Na_c promotes Li-activated K influx. Cellular K inhibits Li-activated K influx, indicating that the interaction of K_c with the internal aspect of the pump is qualitatively different from the interaction with either Na_c or Li_c. The Hill coefficients for Na-promoted and Li-promoted K influx are similar and are both greater than unity, indicating the same number of multiple intracellular sites per pump for the two cations. The stoichiometry of coupling between efflux and K influx is also similar for Na and Li, and is close to 3 Na or 3 Li to 2 K. The Li-activated K influx appears to be independent of the residual Na which remains in cells prepared in Na-free solutions.