Abstract
Some smooth muscles show a peculiar contraction that can preserve a long lasting stretch-resistance with little energy expenditure. Such contraction is called a "catch contraction", and the mechanism to cause a "catch contraction" is referred to as a "catch mechanism". Various approaches have been tried for the study of the "catch mechanism". Nowadays, biochemical and molecular biologists revealed some mechanism by which the "catch state" is regulated on and off.
Previously, relation between the catch mechanism and paramyosin included in a thick myofilament of the catch muscle had attracted attention, but no structural evidences in cells were obtained.
However, thick myofilaments were observed in various catch muscles, and the thick myofilaments showed more than 50-60nm in diameter with few exceptions. It seems that these myofilaments can not contribute to a direct catch mechanism, but it seems likely that the importance of this myofilament will be reaffirmed in future when biochemistry and a molecular biological study comes advance.
