Phosphatidylinositol 4,5-biphosphate stimulates parotid endoplasmic reticulum (Ca2+ + Mg2+)-ATP'ase

The effect of various phospholipids on the (Ca2+ + Mg2+)-ATP'ase of rat parotid endoplasmic reticulum was investigated. At a concentration of 20 micrograms/ml, phosphatidylinositol 4,5-biphosphate stimulated the Ca2+-activated ATP'ase by 69%. None of the other phospholipids tested or 10 microM inositol 1,4,5-triphosphate had any significant effect on the ATP'ase. Stimulation by phosphatidylinositol 4,5-biphosphate was concentration dependent and half maximal stimulation required 8 micrograms/ml of the phospholipid. The results suggest that changes in the cellular concentration of phosphatidylinositol 4,5-biphosphate may be of importance in regulating Ca2+ transport by the endoplasmic reticulum.