[Calcium sensitivity of vascular smooth muscle and effects of drugs].

It has been believed that cytosolic Ca2+ level ([Ca2+]i) is the only regulator of smooth muscle contraction. Measuring [Ca2+]i and muscle force simultaneously, it is evident that changes in Ca2+ sensitivity of contractile elements is also an important regulator. Although the mechanisms for Ca2+ sensitization is not fully understood yet, Ca2+ sensitization of myosin phosphorylation and activation of a Ca(2+)-sensitive mechanism which is not dependent on myosin phosphorylation have been proposed. Receptor-agonists seem to activate both of these mechanisms although protein kinase C does not necessary be involved in these mechanisms.