DISSOCIATION BETWEEN HYSTERESISTIVITY AND TENSION IN CONSTRICTED TRACHEAL AND PARENCHYMAL STRIPS

The object of this study was to investigate how changes in the contrac tile state of smooth muscle would modify oscillatory mechanics of trac heal muscle and lung parenchyma during agonist challenge. Guinea pig t racheal and parenchymal lung strips were suspended in an organ bath. M easurements of length (L) and tension (T) were recorded during sinusoi dal 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 calc ulated by fitting changes in T, L, and Delta L/Delta/t to the equation of motion. Hysteresivity (eta) was obtained from the following equati on: eta = (R/E)2 pi f, 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, pre treatment with Cmz caused a significant decrease in the eta response t o ACh challenge and in maximal unloaded shortening velocity measured d uring electrical field stimulation; Stauro decreased the T, E, and R r esponse to ACh. In parenchymal strips, Cmz decreased the eta response, whereas Stauro had no effect. These results suggest that modification s in the contractile state of the smooth muscle are reflected in chang es in the hysteretic behavior and that T and eta may be controlled ind ependently. Second, inasmuch as changes in eta were similar in parench ymal and tracheal strips, the contractile element is implicated as the structure responsible for constriction-induced changes in the mechani cal behavior of the lung periphery.