Which of the following substances acts to increase the release of Ca2+ from endoplasmic reticulum ?
A. Inositol triphosphate
B. Parathyroid hormone
C. 1,25 dihydroxy cholecalciferol
Correct answer : A. Inositol triphosphate
Inositol 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.