Dissociation between hysteresivity and tension in constricted tracheal and parenchymal strips

The object of this study was to investigatehow changes in the contractile state of smooth muscle would modifyoscillatory mechanics of tracheal muscle and lung parenchyma duringagonist challenge. Guinea pig tracheal and parenchymal lung strips were suspended in an organ bath. Measurements of length(L) and tension (T) were recordedduring sinusoidal oscillations under baseline conditions and afterchallenge with 1 mM ACh. Measurements were also obtained in stripspretreated with the calmodulin inhibitor calmidazolium (Cmz) orstaurosporine (Stauro), a protein kinase C inhibitor. Elastance (E) andresistance (R) were calculated by fitting changes in T,L, andL/tto the equation of motion. Hysteresivity () was obtained from thefollowing equation: = (R/E)2f,where f is frequency. Finally, maximalunloaded shortening velocity during electrical field stimulation wasmeasured in Cmz-pretreated and control tracheal strips. In trachealstrips, pretreatment with Cmz caused a significant decrease in the  response to ACh challenge and in maximal unloaded shortening velocitymeasured during electrical field stimulation; Stauro decreased the T,E, and R response to ACh. In parenchymal strips, Cmz decreased the  response, whereas Stauro had no effect. These results suggest thatmodifications in the contractile state of the smooth muscle arereflected in changes in the hysteretic behavior and that T and  maybe controlled independently. Second, inasmuch as changes in  weresimilar in parenchymal and tracheal strips, the contractile element isimplicated as the structure responsible for constriction-induced changes in the mechanical behavior of the lung periphery.