What second messenger most directly causes calcium ions to be released from intracellular stores?

a. Diacylglycerol

b. Adenylyl cyclase inositol trisphosphate

c. Phospholipase A

d. Phospholipase C

Answer: adenylyl cyclase inositol triphosphate mainly known as IP3 causes the release of Calcium ions directly from the inracellular stores and causea contraction.

Explanation:

IP3, inositol phosphate is a second messenger a signaling molecule. It is made by hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2), a phospholipid that is located in the plasma membrane, by an enzyme phospholipase C.

IP3 binds to the calcium channels and opens Ca2 + channels that are embedded in the ER membrane, releasing Ca2 + into the cytosol. Calcium ions released may cause contraction and regulate the Ca2 + channels in the membranes.