Calcium permeability of Ehrlich ascites tumour cell plasma membrane in vivo.

Passive Ca2+ entry into Ehrlich ascites tumour cells has been investigated. Passive equilibrium of Ca2+ takes place in ascites tumour cells only under conditions of exhaustive energy depletion. The specific Ca2+ ionophore A23187 does not affect Ca2+ entry into ascites tumour cells under active metabolic conditions, but it increases the rate of Ca2+ equilibration in ascites tumour cells in the early stages of energy depletion. The results of the present experiments lead to the conclusion that in ascites tumour cell plasma membrane Ca2+ permeability is not a limiting step in the regulation of intracellular calcium content, while the energy-dependent Ca2+ extrusion is the main mechanism that prevents uncontrolled intracellular Ca2+ increase. The results taken together support the hypothesis that increased Ca2+ influx into the cell, caused by plasma membrane alteration, is responsible for permanently elevated mitotic activity and for deranged metabolic behavior of these neoplastic cells.