Mechanical strain memory in airway smooth muscle

We investigated the effect of a single rapid stretch on poststretch force a nd myosin phosphorylation in bovine tracheal smooth muscle. When unstimulat ed muscle strips were stretched from suboptimal length to optimal length (L -0), poststretch steady-state force was not significantly different from th at of unstretched control at L-0. However, when carbachol-activated muscle strips were stretched from suboptimal length to L-0, poststretch force and myosin phosphorylation were lower than control and significantly correlated with initial length. When poststretch muscle strips were allowed to relax for 1 h and then activated by K+ depolarization, the developed force remain ed significantly correlated with initial length. When the same strain was a pplied in 23 increments to minimize peak stress, poststretch force and myos in phosphorylation increased significantly, approaching the levels expected at L-0. Furthermore, poststretch force development increased after each cy cle of contraction and relaxation, approaching the control level after four cycles. These results suggest that activated airway smooth muscle cells ca n retain relatively precise memory of past strain when they are stretched r apidly with high stress.