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D-myo-Inositol-1,3,4,5-tetraphosphate (Ins(1,3,4,5)-P₄) is formed by the phosphorylation of Ins(1,4,5)P₃ by inositol 1,4,5-triphosphate 3-kinase. Ins(1,3,4,5)-P₄ increases intracellular calcium levels by two distinct mechanisms: opening calcium channels on both the endoplasmic reticulum to release calcium from internal stores and on the plasma membrane to allow the influx of calcium from outside the cell.