Dissociation between hysteresivity and tension in constricted tracheal and parenchymal strips

The object of this study was to investigate how changes in the contractile state of smooth muscle would modify oscillatory mechanics of tracheal muscle and lung parenchyma during agonist challenge. Guinea pig tracheal and parenchymal lung strips were suspended in an organ bath. Measurements of length (L) and tension (T) were recorded during sinusoidal oscillations under baseline conditions and after challenge with 1 mM ACh. Measurements were also obtained in strips pretreated with the calmodulin inhibitor calmidazolium (Cmz) or staurosporine (Stauro), a protein kinase C inhibitor. Elastance (E) and resistance (R) were calculated by fitting changes in T, L, and DeltaL/Deltat to the equation of motion. Hysteresivity (eta) was obtained from the following equation: eta = (R/E)2pif, where f is frequency. Finally, maximal unloaded shortening velocity during electrical field stimulation was measured in Cmz-pretreated and control tracheal strips. In tracheal strips, pretreatment with Cmz caused a significant decrease in the eta response to ACh challenge and in maximal unloaded shortening velocity measured during electrical field stimulation; Stauro decreased the T, E, and R response to ACh. In parenchymal strips, Cmz decreased the eta response, whereas Stauro had no effect. These results suggest that modifications in the contractile state of the smooth muscle are reflected in changes in the hysteretic behavior and that T and eta may be controlled independently. Second, inasmuch as changes in eta were similar in parenchymal and tracheal strips, the contractile element is implicated as the structure responsible for constriction-induced changes in the mechanical behavior of the lung periphery.