Release of Ca2 from endoplasmic reticulum | Frequently Asked Medical PG topics

Release of Ca2 from endoplasmic reticulum is increased by 
A. Inositol triphosphate 
B. Parathyroid hormone 
C. 125-dihydroxycholecalciferol 
D. Diacylglycerol

Ans.A. Inositol triphosphate.  

Explanation: When a ligand binds to a receptor on the membrane, the receptor gets activated, which in turn activates phospholipase C through the G proteins. Phospholipase C catalyzes the hydrolysis of PiP, phosphatidylinositol 4, 5 diphosphate.  to IF2 inositol triphosphate.  and DAG. IF3 diffuses to the endoplasmic reticulum, where it triggers the release of Ca2 into cytoplasm. Now the free calcium can bind to the calcium-binding protein to show some physiological effect.