“The enzymatic synthesis …,5-bisphosphate PtdIns (4,5)P2 ) was maximally enhanced by 0.… by micromolar concentrations of Ca2−. Inhibition of PtdIns and PtdIns4P kinase showed IC50 values for Ca2+ of 20 and 6 … of either Ca2+-induced activation of phospholipase C and polyphosphoinositide monophosphoesterases or low ATP concentrations.”