We compared the inhibitory effects of calcium channel blockers, gallopamil and verapamil on acetylcholine (Ach)-induced contractions of ovine tracheal muscle in vitro. Adult sheep were sacrificed and tracheal strips were obtained by cutting the single tracheal rings from the mid-trachea. Tracheal strips were suspended in Krebs-Henseleit solution and isometric tension measured upon stimulation with cumulative doses of Ach (10-7 to 10-4M) without and after pretreatment with gallopamil (10-7 to 10-6 M) or verapamil (10-6 to 10-5 M). In untreated tissues, the mean concentration of Ach required to produce 50% of maximal response (EC50) was 4.3 x 10-6M Ach. Both gallopamil and verapamil inhibited the Ach-induced contractions of ovine tracheal smooth muscle, by shifting the dose-response curves to Ach to the right. EC50 Ach for gallopamil (10-6 M) and verapamil (10-6 M) was 2.6 x 10-5 and 5.2 x 10-6 M, respectively. Dose ratio defined as postantagonist EC50 Ach/control EC50 Ach, was 7.7 for gallopamil and 2.0 for verapamil. Thus, the inhibitory effect of gallopamil was approximately 4-fold more potent than that of verapamil. Gallopamil was 17-fold more potent than verapamil in relaxing precontracted tracheal strips. The dose of calcium antagonists required to produce 25% relaxation (EC25) of tracheal strips precontracted with 10-4 Ach was 3.7 x 10-5 M for verapamil and 2.2 x 10-6 M for gallopamil. These results indicate that gallopamil is effective against Ach-induced contractions of ovine trachealis muscles, and is more potent than verapamil.
- Airway smooth muscle
- Calcium antagonist
ASJC Scopus subject areas
- Pulmonary and Respiratory Medicine