<prompt> Which of the following substances acts to increase the release of Ca2 from endoplasmic reticulum?Inositol triphosphateParathyroid hormone1,25 dihydroxy cholecalciferolDiacylglycerol  <response>: Ans. A. Inositol triphosphateInositol triphosphate IP3 and diacylglycerol DAG are second messengers for G protein coupled receptors. IP3 stimulates release of calcium from endoplasmic reticulum. DAG activates protein kinase C. 