Influence of intercellular tissue connections on airway muscle mechanics

Contraction ofsmooth muscle in visceral organs is modified by structures external tothe muscle. Within muscle tissue itself, connective tissue plays animportant role in force transference among the contractile cells.Connections arranged radially can affect contractile mechanics bylimiting tissue expansion at short lengths. Previous work suggests thatincreased stiffness at extreme shortening is due to such radialconstraints. Two approaches to further study of these effects arereported. To increase radial constraints, very thin Silastic bands wereplaced loosely about strips of canine trachealis muscle at rest length.The strips were allowed to shorten under light afterloads, expandinguntil restrained by the bands. Subsequent removal of the bands allowed increased shortening, with less increase in stiffness at short lengths.Related isometric effects were observed. To reduce constraints, musclestrips were partially digested with collagenase. Compared with controlconditions, this treatment permitted further shortening, with lessincrease in stiffness at short lengths. These results emphasize therole of extracellular structures in determining mechanical function ofsmooth muscle.