Fig. 5. PI(4,5)P₂ regulates Ca²⁺ extrusion and a more detailed model of the Ca²⁺ regulatory system.

(A) PM localization of NCS1-mCherry increased when cytosolic Ca²⁺ was raised (see also movie S1). (B) Quantification comparing NCS1 localization in low and high cytosolic Ca²⁺ (P value from two-tailed paired Student’s t test, n = 7). AU, arbitrary unit. (C) Fura-2 measurements of Ca²⁺ extrusion after rapid release from the ER by ionomycin. Inset shows quantification of the effect of reducing PI(4,5)P₂ abundance by INP54P overexpression on Ca²⁺ extrusion (P value from two-tailed Student’s t test, n≥6; error bars show SEM). (D) More detailed molecular model of the Ca²⁺ regulatory systeminHEK293T cells. Specific isoforms and regulators are shown with their predicted functions derived from our computational analysis of time-course differences in the siRNA perturbation experiments. The circle below PIP₂ represents a sink resulting from the degradation of this molecule. PIP₂, PI(4,5)P₂.