EFFECT OF CYCLOSPORINE-A ON CA2-CELLS( FLUXES AND THE RATE OF RESPIRATION IN EHRLICH ASCITES TUMOR)

Cyclosporin A at micromolar concentration decreases the respiration of Ehrlich ascites tumour cells (with pyruvate as substrate) but prevent s the inhibition of oxygen uptake produced by glucose or deoxyglucose (the Crabtree effect). Cyclosporin A also diminishes the increase of c ytoplasmic free Ca2+ concentration elicited by deoxyglucose and almost completely abolishes this increase induced by extracellular ATP and t hapsigargin but does not decrease the size of endoplasmic reticulum Ca 2+ stores as revealed after addition of ionomycin. It is concluded tha t cyclosporin A inhibits the inositol trisphosphate-sensitive Ca2+ cha nnel and the passive permeability of the endoplasmic reticulum to Ca2 in Ehrlich ascites tumour cells.