THE ROLE OF CYTOPLASMIC [CA2-INDUCED INHIBITION OF RESPIRATION AND OXIDATIVE-PHOSPHORYLATION IN EHRLICH ASCITES TUMOR-CELLS - A NOVEL MECHANISM OF THE CRABTREE EFFECT(] IN GLUCOSE)

The effect of Ca2+ on energy-coupling parameters of Ehrlich ascites ca rcinoma 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 potenti al (Delta psi) and alkalinization of the medium. This typical behaviou r is drastically changed if Ca2+ is added. The subsequent addition of ADP induces neither State 3 respiration, nor decrease of Delta psi, no r alkalinization of the medium, indicating a complete block of ATP syn thesis. These effects are produced by both a single pulse of 100 mu M Ca2+ and a preincubation for 2 min with 0.4-1.0 mu M Ca2+. Preincubati on of the cells with glucose or deoxyglucose prior to permeabilization makes them sensitive to Ca2+ concentrations as low as 0.3 mu M. In vi ew of the previous finding that glucose and deoxyglucose produce an in crease of cytoplasmic [Ca2+] in Ehrlich ascites cells [Teplova VV. Bog ucka K. Czyz A. Evtodienko YuV. Duszyriski J. Wojtczak L. (1993) Bioch em. Biophys. Res. Commun., 196, 1148-1154; Czyz A. Teplova VV. Sabala P. Czamy M. Evtodienko YuV. Wojtczak L. (1993) Acta Biochim. Polon., 4 0, 539-544], the present results suggest that cytoplasmic Ca2+ plays a crucial role in the Crabtree effect.