The role of Pi in glycolytic inhibition of calcium ion uptake by ELD ascites tumor cells

Cell signaling and cancer-possible targets for therapy

Tumor progression involves the acquisition of properties which include growth-factor independent cell proliferation, failure of inhibition by growth-inhibitory signals, ability to invade surrounding tissues, and to evade apoptosis, etc. Characterization of the profile or molecular signature of the tumor may permit the development of rational therapies that target the aberrant pathways. Rapidly growing tumor cells are usually associated with a high rates of glycolysis and in these cells, it may be advantageous to exploit this pathway which most likely is required for optimal synthetic needs. Combinatorial therapeutic agents which target the growth factor signal transduction pathways as well as apoptotic signaling pathways provide an opportunity for maximal therapeutic benefit.

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.

Effects of amino acids on calcium uptake by glial and neuroblastoma cells

The uptake of [45Ca] has been studied in clonal glial and neuronal cells. It was somewhat more efficient in the neuroblastoma clone M1 compared to glial clones. In all cases [45Ca] uptake was shown to depend on the phosphate concentration in the incubation medium. It was decreased by the ionophore A 23187 at 200 microM concentration in both neuronal and glial clones. The influence of amino acids some of which are putative neurotransmitters was investigated; the interactions between [45Ca] uptake and these amino acids were related to their concentration and the type of cells used (neuronal or glial). L-aspartate and taurine for example had two opposite effects on [45Ca] uptake by the glial clone NN at two different concentrations; they could therefore play a role in the control of calcium level in the synaptic cleft.

Calcium-ion transport by intact Ehrlich ascites-tumour cells. Role of respiratory substrates, Pi and temperature

1. The interaction of intact Ehrlich ascites-tumour cells with Ca2+ at 37 degrees C consists of Ca2+ uptake followed by efflux from the cells. Under optimum conditions, two or three cycles of uptake and efflux are observed in the first 15 min after Ca2+ addition. 2. The respiratory substrates malate, succinate and ascorbate plus p-phenylenediamine support Ca2+ uptake. Ca2+ uptake at 37 degrees C is sensitive to the respiratory inhibitors rotenone and antimycin A when appropriate substrates are present. Ca2+ uptake and retention are inhibited by the uncoupler S-13. 3. Increasing extracellular Pi (12 to 30 mM) stimulates uncoupler-sensitive Ca2+ uptake, which reaches a maximum extent of 15 nmol/mg of protein when supported by succinate respiration. Ca2+ efflux is partially inhibited at 30 mM-Pi. 4. Optimum Ca2+ uptake occurs in the presence of succinate and Pi, suggesting that availability of substrate and Pi are rate-limiting. K. Ca2+ uptake occurs at 4 degrees C and is sensitive to uncouplers and oligomycin. Ca2+ efflux at this temperature is minimal. These data are consistent with a model in which passive diffusion of Ca2+ through the plasma membrane is followed by active uptake by the mitochondria. Ca2+ uptake is supported by substrates entering respiration at all three energy-coupling sites. Ca2+ efflux appears to be an active process with a high temperature coefficient.