label AsT PT CaT "no PO4 + 0.2 mM Ca" 0. 0. 0.2 "0.25 mM PO4 + 0.2 mM Ca" 0. 0.25 0.2 "0.50 mM PO4 + 0.2 mM Ca" 0. 0.5 0.2