Final answer:
Upon the action of inositol trisphosphate (IP3), the cytoplasmic Protein Kinase C (PKC) is activated by the release of Ca2+ ions into the cytoplasm, which also requires the presence of diacylglycerol (DAG).
Step-by-step explanation:
When Ca2+ is released by the action of inositol triphosphate (IP3), the cytoplasmic protein that it activates is Protein Kinase C (PKC). Once IP3 is formed by the action of the enzyme phospholipase C, it diffuses into the cytoplasm and binds to ligand-gated calcium channels in the endoplasmic reticulum, which prompts the release of Ca2+ into the cytoplasm. The increase in cytoplasmic Ca2+ concentration, along with diacylglycerol (DAG) which remains in the plasma membrane, simultaneously activates PKC. PKC then initiates a phosphorylation cascade by adding phosphate groups to serine and threonine residues on target proteins, leading to cell-specific responses and physiological effects.