<prompt> Increase in cytosolic calcium from intracellular storage, during smooth muscle contraction, isare due to -cAMPcGMPcCMPIP3-DAG  <response>: The release of Ca from intracellular source, that is sarcoplasmic reticulum, is by IP3-DAG second messenger system, whereas the pumping of Ca from extracellular space to cytosol is by Ca channels. IP3 when bound to its receptors on sarcoplasmic reticulum, causes the release of calcium into sarcoplasm. 