Effect of glucose and deoxyglucose on the redistribution of calcium in ehrlich ascites tumour and Zajdela hepatoma cells and its consequences for mitochondrial energetics. Further arguments for the role of Ca(2+) in the mechanism of the crabtree effect

The distribution of Ca(2+) in intact cells was monitored with fluorescent probes: fura-2 for cytosolic [Ca(2+)] and rhod-2 for mitochondrial [Ca(2+)]. It was found that in neoplastic cells, such as Ehrlich ascites tumour and Zajdela hepatoma, but not in non-malignant cells, such as fibroblasts, glucose and deoxyglucose elicited release of Ca(2+) from endoplasmic reticulum stores and an increase in Ca(2+) concentration in the cytosol. Parallel to this, a decrease in the rate of Ca(2+) extrusion from the cell and an enhanced uptake of Ca(2+) by mitochondria were observed. The increase in mitochondrial [Ca(2+)] was accompanied by an increase in the mitochondrial membrane potential and the reduction state of nicotinamide nucleotides. F(1)F(o)-ATPase in submitochondrial particles of Zajdela hepatoma was strongly inhibited in the presence of micromolar Ca(2+) concentrations, whereas this activity in submitochondrial particles from rat liver appeared to be less sensitive to Ca(2+). Indications of glycosylation of Ehrlich ascites tumour cell proteins were also obtained. These data strengthen the proposal [Bogucka, K., Teplova, V.V., Wojtczak, L. and Evtodienko, Y. V. (1995) Biochim. Biophys. Acta 1228, 261-266] that the Crabtree effect is produced by mobilization of cell calcium, which is subsequently taken up by mitochondria and inhibits F(1)F(o)-ATP synthase.

Inhibition by Ca2+ of the hydrolysis and the synthesis of ATP in Ehrlich ascites tumour mitochondria: relation to the Crabtree effect

Phosphorylation of ADP and hydrolysis of ATP by isolated mitochondria from Ehrlich ascites tumour cells is greatly reduced when the mitochondria have been preloaded with Ca2+ (50 nmol/mg protein or more). Translocation of ADP is diminished in Ca(2+)-loaded mitochondria. However, ATPase in toluene-permeabilized mitochondria and in inside-out submitochondrial particles is also strongly inhibited by micromolar concentrations of Ca2+, indicating that, independently of adenine nucleotide transport, F1Fo-ATPase is also affected. ATP hydrolysis by submitochondrial particles depleted of the inhibitory subunit of F1Fo-ATPase (the Pullman-Monroy protein inhibitor) is insensitive to Ca2+; however, this sensitivity is restored when the particles are supplemented with the inhibitory subunit isolated from beef heart mitochondria. In view of the previous observations that glucose elicits in Ehrlich ascites tumour cells an increase of cytoplasmic free Ca2+ (Teplova, V.V., Bogucka, K., Czyz, A., Evtodienko, Yu.V., Duszyński, J. and Wojtczak, L. (1993) Biochem. Biophys. Res. Commun. 196, 1148-1154) and that this calcium is then taken up by mitochondria, resulting in a strong inhibition of coupled respiration (Evtodienko, Yu.V., Teplova, V.V., Duszyński, J., Bogucka, K. and Wojtczak, L. (1994) Cell Calcium 15, 439-446), the present results are discussed in terms of the mechanism of the Crabtree effect in tumour cells.

The role of cytoplasmic [Ca2+] in glucose-induced inhibition of respiration and oxidative phosphorylation in Ehrlich ascites tumour cells: a novel mechanism of the Crabtree effect

The effect of Ca2+ on energy-coupling parameters of Ehrlich ascites carcinoma was studied in digitonin-permeabilized cells. In nominally Ca-free medium the permeabilized cells respond to the addition of ADP by increased oxygen uptake with externally added respiratory substrates (succinate or pyruvate), decrease of the mitochondrial membrane potential (delta psi) and alkalinization of the medium. This typical behaviour is drastically changed if Ca2+ is added. The subsequent addition of ADP induces neither State 3 respiration, nor decrease of delta psi, nor alkalinization of the medium, indicating a complete block of ATP synthesis. These effects are produced by both a single pulse of 100 microM Ca2+ and a preincubation for 2 min with 0.4-1.0 microM Ca2+. Preincubation of the cells with glucose or deoxyglucose prior to permeabilization makes them sensitive to Ca2+ concentrations as low as 0.3 microM. In view of the previous finding that glucose and deoxyglucose produce an increase of cytoplasmic [Ca2+] in Ehrlich ascites cells [Teplova VV. Bogucka K. Czyz A. Evtodienko YuV. Duszyński J. Wojtczak L. (1993) Biochem. Biophys. Res. Commun., 196, 1148-1154; Czyz A. Teplova VV. Sabala P. Czarny M. Evtodienko YuV. Wojtczak L. (1993) Acta Biochim. Polon., 40, 539-544], the present results suggest that cytoplasmic Ca2+ plays a crucial role in the Crabtree effect.