EXCITATION AND CONTRACTION OF THE SMOOTH MUSCLE

Morphological, chemical and mechanical aspects of the excitation and contraction in the visceral smooth muscle, concerning chiefly with the results obtained in our laboratory, were reviewed. There exsist essentially no qualitative differences between the nature of the contractile proteins of the smooth muscle and those of the skeletal muscle. Some quantitative differences between these proteins and their location (arrangement) in the cell, however, seem to be the characteristics of the smooth muscle. From the results in the biochemical experiments on the vesicular system, probably including mitochondria, of the smooth muscle, it was suggested that this system has a pumping function extruding Ca ion from the cell. Further investigations would be the important key in the investigation of the E-C link mechanism. On the other hand, it has been reported that the presence of the extracellular Ca is extremely important in the excitation and contraction of the smooth muscle. These results indicate that extracellular Ca fluxes into the cell during the excitation of the membrane and activates directly the contractile proteins. The characteristic mechanism which induces the contraction of the smooth muscle was discussed.