Calmodulin (CALM2) binds to calicium to regulate calicium function.  It is calicium primary receptor to regulate calicium functions.  Calicium regulate as a intracellural communication.  "In order for calcium to act out its role as regulator, it must form a complex with calcium. The following scheme represents the way in which calmodulin and other calcium binding proteins form a complex with calcium."(Calmodulin 1).  Hormon are first messenger that bind to the plasma memebrane to signal second messenger intracellular.  Adenylate is an enzyme that catalyze ATP to cAMP.  And the signaling messengers goes on.  In order for Adenylate and cAMP to work they must beind to complex formed calmodulin and calicium.(Calmodulin 1).   An increase of calicium intracellular, causes calmodulin to bind with calicium.  The binding produces calmoduline ATPs.  These CaATPs causes calicium to be realesed from cytoplasm. 

For muscle to contract, it uses two proteins actin and myosin.  "For a muscle to contract, intracellular calcium concentration must increase. The increased calcium concentration enables actin to interact with myosin. Actin-myosin interaction activates actomyosin ATPase which extracts energy from ATP for contraction.  In skeletal and cardiac muscle, the calcium dependent activation of actomyosin ATPase is mediated by the troponin-tropomyosin complex. In smooth muscle and nonmuscle cells, regulation occurs at the level of myosin and consists of the calcium dependent phosphorylation of the two regulatory light chains of myosin. This phosphorylation is reversible. These reactions in smooth muscle are catalyzed by the myosin light chain kinases and phosphatases. Calmodulin is the regulator of calcium action for myosin light chain kinases and phosphatases."(Calmodulin 2).