Contraction in the smooth muscle cell

This paper advances the hypothesis that the rearrangement of the actin cyto skeleton that takes place during contraction in the SMC is a mechanical ref lection of the spatiotemporal pattern of the cell's polarized stimulus. In that sense the cell is responding more like a motile non-muscle cell than l ike a skeletal muscle cell. The paper reviews how diffusion patterns are ge nerated and modified and suggests how the patterns are detected by the cell and transduced into cytoskeletal movement. Evidence is presented suggestin g the actin cytoskeleton is composed of conical-shaped myofibrils (contract ile units) measuring half a cell in length and containing filament-free spa ces at their centres filled with cell inclusions. It is argued that the SMC contracts by involving variable combinations of the myofibrils in sequence and that the cell takes advantage of that fact to translocate various cont ractile elements between the myofibrils during contraction, thus economizin g on its needs for those elements. Among the elements translocated are thou ght to be myosin, SR and mitochondria. (C) 1999 Harcourt Publishers Ltd.