Fig. (1) Endothelial nitric oxide production and it actions in the vascular smooth muscle cell. ACh= acetylcholine; BK= bradykinin; ATP= adenosine triphosphate; ADP= adenosine diphosphate; SP= substance P; SOCa²⁺= store-operated Ca²⁺ channel; ER= endoplasmic reticulum; NO= nitric oxide; sGC= soluble guanylyl cyclase; cGMP= cyclic guanosine-3’, 5-monophosphate; MLCK= myosin light chain kinase. *When Ca²⁺ stores of the endoplasmic reticulum are depleted a signal is sent to SOCa²⁺ channel which allows extracellular Ca²⁺ into the endothelial cell.