| Research Abstract |
It is generally accepted that smooth muscle contraction is regulated by Ca^<2+>-dependent phosphorylation of myosin light chain and subsequent interaction with actin. Recently, several reports suggested that some actin binding proteins, such as caldesmon and calponin, change the actin-myosin interaction in vitro. At present, however, it is unclear if such mechanisms are involved in the contraction of intact smooth muscle. In this study, we defined several novel findings by analyzing the effects of several types of agonists on cytosolic Ca^<2+> concentration, myosin phosphorylation and contractility of intact and skinned muscles.
Summary
I. In vascular and tracheal smooth muscles, the following mechanisms seemed to be involved in the contraction ;
i)Ca^<2+>-dependent myosin phosphorylation
ii)Increase in Ca^<2+> sensitivity of myosin phosphorylation
iii)Ca^<2+> -dependent and myosin phosphorylation-independent mechanism
II. The mechanisms of contraction, as mentioned above, are due to an active actin/myosin interaction.
III. Actin regulated mechanisms may be involved in the above mechanisms. Since the effects of phorbol esters mimic the agonists-induced contraction, activation of protein kinase C may be involved in the above mechanisms, although further experiments are necessary to clarify the role of protein kinase C.
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