Thick filaments in vertebrate smooth muscle.
Smooth muscle cells of the mouse vas deferens fixed with 5% glutaraldehyde contained three types of filaments, namely, thin (50-80) A) filaments, intermediate (100 A) filaments and thick (120-180 A) filments. However, in 2 out of 16 experiments, under identical conditions, the cells did not contain thick filaments. With OSO4 fixation, thin filaments were not prominent, the most obvious being thick (120-250 A) and intermediate (100 A) filaments. After soaking in a modified Ringer solution under no applied tension for one hour, thick filaments (120-180 A) appeared prominently in smooth muscle cells of the mouse vas deferens and thin filaments were in ordered bundles. By 4 hours, thick filaments had increased in size and density, with thin filaments distributed randomly around them. After 8 hours in Ringer, thin filaments were diffuse and difficult to discern, while thick filaments were large (up to 300 A) and electron-dense. Intermediate (100 A) filaments were present in association with dark bodies. Physiological experiments indicated that the intracellular components responsible for the development of a mechanical response were still functional at this time. The presence of "thick filaments" is also reported in degenerating smooth muscle cells of the guinea-pig vas deferens in tissue culture.
D000199:Actins; D000818:Animals; D046508:Culture Techniques; D006168:Guinea Pigs; D008297:Male; D008854:Microscopy, Electron; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000166:cytology*; D009210:Myofibrils / Q000648:ultrastructure*; D009218:Myosins; D009638:Norepinephrine / Q000494:pharmacology; D012996:Solutions; D013997:Time Factors; D014649:Vas Deferens / Q000648:ultrastructure
D000199:Actins; D012996:Solutions; D009218:Myosins; D009638:Norepinephrine