The effect of Lanthanum on electrophoretic mobility and passive cation movements of the ehrlich ascites tumor cell

We have investigated the effects of La +3 binding to the surface of Ehrlich ascites tumor cells on cell electrophoretic mobility and passive movements of Na + and K + . Incubation of tumor cells in La +3 ‐containing media results in a La +3 concentration‐dependent decrease in net surface charge negativity. At [La +3 ] greater than 0.5 mM, the net surface charge becomes positive with maximum positivity occurring at [La +3 ] = 0.9 mM. The effects of La +3 binding on passive Na + and K + movements were investigated by following 22 Na and K + losses from ouabain‐inhibited cells. Neither low (0.02) nor high (1.0 mM) [La +3 ] had any effect on the K + efflux rate coefficient. 22 Na losses from control and La +3 ‐treated cells were consistent with washouts from two cellular compartments. Low [La +3 ] (0.02 mM) was without effect on Na + loss from the cells. However, higher [La +3 ] (1.0 mM) resulted in a 48% inhibition of Na + loss from the more slowly exchanging compartment. These results are not consistent with simple electrostatic interactions exerting a major influence on the passive movements of Na + and K + . It is suggested that La +3 interacts with sites specific for Na + , perhaps involved in a carrier‐mediated exchange system.