Figure 3: General scheme of excitation-contraction coupling in airway myocyte. Ca2+ increase, either via InsP3-induced Ca2+ release from the sarcoplasmic reticulum (SR) of extracellular influx, binds to calmodulin (CaM). The Ca2+-CaM complex binds to and activates the myosin light chain kinase (MLCK) that phosphorylates the regulatory myosin light chain. Phosphorylated myosin (Mp) can bind to actin (A) to form the phosphorylated actomyosin bridge (AMp). Myosin, either bound (AMp) or unbound to actin (Mp) is dephosphorylated by the myosin light chain phosphatase (MLCP). Actomyosin bridge, either phosphorylated or not, corresponds to contraction, whereas myosin unbound to actin corresponds to relaxation.