Selected contribution:: Effect of chronic passive length change on airway smooth muscle length-tension relationship

The ability of rabbit trachealis to undergo plastic adaptation to chronic shortening or lengthening was assessed by setting the muscle preparations at three lengths for 24 h in relaxed state: a reference length in which applied force was similar to1-2% of maximal active force (P-o) and lengths considerably shorter and longer than the reference. Passive and active length-tension (L-T) curves for the preparations were then obtained by electrical field stimulation at progressively increasing muscle length. Classically shaped L-T curves were obtained with a distinct optimal length (L-o) at which P-o developed; however, both the active and passive L-T curves were shifted, whereas P-o remained unchanged. L-o was 72% and 148% that of the reference preparations for the passively shortened and lengthened muscles, respectively. The results suggest that chronic narrowing of the airways could induce a shift in the L-T relationship of smooth muscle, resulting in a maintained potential for maximal force production.