Lanthanum‐Induced alterations in cellular electrolytes and membrane potential in ehrlich ascites tumor cells

We have investigated the effect of varying La⁺³ concentrations (0.01 mM to 2.0 mM) on membrane potential and electrolyte composition of Ehrlich ascites tumor cells. La⁺³ concentrations less than 0.02 mM had no effect. Above 0.02 mM, La⁺³ induced concentration‐dependent loss of electrolytes and water from the cells. At 1.0 mM the effect was maximal and resulted in an 87% reduction in cellular K⁺, 79% in Cl⁻ and 21% in Na⁺ within 4.8 minutes. The Na⁺ loss occurred even in the face of an electrochemical potential gradient favoring Na⁺ entry. La⁺³ increased the recorded values of membrane potential; the magnitude of the effect was related to the external La⁺³ concentration, and was maximal at 1.0 mM. Studies using ¹⁴⁰La showed that La⁺³ binds rapidly to the cell surface and does not enter the cells. The amount of La⁺³ bound to the cells was related to the external La⁺³ concentration by a sigmoidal curve and was maximal at about 1.0 mM. The bound La⁺³ could not be displaced by either added La⁺³ or Ca⁺². Agents known to effect the integrity of the cell membrane, such as phospholipase C, neuraminidase, pronase and Hg⁺² were tested for their ability to displace bound La⁺³. Only pronase displaced bound La⁺³, indicating that La⁺³ associates with cell protein. It is hypothesized that La⁺³ rapidly interacts with membrane protein causing alterations in membrane permeability and capacity to actively transport ions.