It is evident that smooth muscle contraction is regulated not only by the Ca2+/calmodulin/myosin light chain kinase system but also by modulation of Ca2+ sensitivity. Changes in free calmodulin concentrations, myosin light chain phosphorylation elicited by rho/rho-kinase, regulation of myosin phosphatase activity and thin filament-linked mechanisms are the possible mechanisms for regulation of Ca2+ sensitivity.