We have reported previously that in ovalbumin-sensitized canine tracheal smooth muscle (TSM) the maximum ability to shorten is increased. This could account for the increased airway narrowing seen in vivo in allergic bronchoconstriction. It was associated with increased velocity of shortening. We now report that, by using an electromagnetic muscle lever system, quick releases were applied to control and sensitized TSM at 0.5-s intervals throughout the course of a lightly preloaded 10-s isotonic contraction. From the records obtained it is possible to determine that, early in contraction, shortening is brought about by relatively rapidly cycling [0.35 optimal muscle length units +/- 0.033/s (SE)] cross bridges. We also report that in the sensitized TSM it is the early bridges that increase their velocity by 26.6% (P less than 0.05) compared with similar bridges in muscles from control animals. Since 70% of the maximum shortening of the muscle occurs when early bridges are operative, it is likely that these bridges are responsible for the major part of the shortening. It is thus probable that increased allergic bronchoconstriction is produced by increased activity of early, rapidly cycling bridges. The bridges that are active late in the shortening show no difference between control and sensitized airway smooth muscles.
Dense bodies in smooth muscle are thought to be the equivalents of Z-disks found in striated muscle. Using three-dimensional reconstruction of serial sections of electron micrographs of ASM, we have confirmed previous studies showing that dense-body (DB) aggregates inside smooth muscle cells resemble "stringy" structures lying in parallel with
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.