Effect of cyclosporin A on Ca2+ fluxes and the rate of respiration in Ehrlich ascites tumour cells.

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