EFFECT OF AIRWAY INFLAMMATION ON SMOOTH-MUSCLE SHORTENING AND CONTRACTILITY IN GUINEA-PIG TRACHEALIS

We studied the effect of either 1) immunogenic inflammation caused by aerosolized ovalbumin or 2) neurogenic inflammation caused by aerosoli zed capsaicin in vivo on guinea pig tracheal smooth muscle (TSM) contr actility in vitro. Force-velocity relationships were determined for ni ne epithelium-intact TSM strips from ovalbumin-sensitized (OAS) vs. se ven sham-sensitized controls and TSM strips for seven animals treated with capsaicin aerosol (Cap-Aer) vs. eight sham controls. Muscle strip s were tethered to an electromagnetic lever system, which allowed isot onic shortening when load clamps [from 0 to maximal isometric force (P (o))] were applied at specific times after onset of contraction. Contr actions were elicited by supramaximal electrical field stimulation (60 Hz, 10-s duration, 18 V). Optimal length for each muscle was determin ed during equilibration. Maximal shortening velocity (V(max)) was incr eased in TSM from OAS (1.72 +/- 0.46 mm/s) compared with sham-sensitiz ed animals (0.90 +/- 0.15 mm/s, P < 0.05); V(max) for TSM from Cap-Aer (0.88 +/- 0.11 mm/s) was not different from control TSM (1.13 +/- 0.0 8 mm/s, P = NS). Similarly, maximal shortening (DELTA(max)) was augmen ted in TSM from OAS (1.01 +/- 0.15 mm) compared with sham-sensitized a nimals (0.72 +/- 0.14 mm, P < 0.05); DELTA(max) for TSM from Cap-Aer a nimals (0.65 +/- 0.11 mm) was not different from saline aerosol contro ls (0.71 +/- 0.15 mm, P = NS). We demonstrate V(max) and DELTA(max) ar e augmented in TSM after ovalbumin sensitization; in contrast, neuroge nic inflammation caused by capsaicin has no effect on isolated TSM con tractility in vitro. These data suggest that airway hyperresponsivenes s in vivo that occurs in association with immunogenic or neurogenic in flammation may result from different effects of these types of inflamm ation on airway smooth muscle.