Mechanical strain memory in airway smooth muscle

We investigated the effect of a single rapid stretch on poststretch force and myosin phosphorylation in bovine tracheal smooth muscle. When unstimulated muscle strips were stretched from suboptimal length to optimal length (L-0), poststretch steady-state force was not significantly different from that 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 remained significantly correlated with initial length. When the same strain was applied in 23 increments to minimize peak stress, poststretch force and myosin phosphorylation increased significantly, approaching the levels expected at L-0. Furthermore, poststretch force development increased after each cycle of contraction and relaxation, approaching the control level after four cycles. These results suggest that activated airway smooth muscle cells can retain relatively precise memory of past strain when they are stretched rapidly with high stress.