| Abstract: | 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 22Na 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. 22Na 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+ losses 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. |
