The interaction of neuromuscular relaxants with rabbit lung muscarinic receptors

The interaction of muscle relaxants with airway muscarinic receptors of rabbit lung was investigated in vitro by the [3H]QNB binding technique. Pancuronium, vecuronium, alcuronium and succinyl choline chloride (SCC) inhibited the binding of [3H]QNB to rabbit lung muscarinic receptors in a dose‐dependent manner. The values of IC50 (the concentration giving 50% inhibition) of pancuronium, vecuronium, alcuronium and SCC were 1.54 times 10‐5, 2.52 times 10‐5, 8.40 times 10‐5, and 4.00 times 10‐3 moll respectively. As the values of Kd increased with minimal change in the value of Bmax, while not influencing the number of receptors, these muscle relaxants had an inhibitory action on the affinity of muscarinic receptors to [3H]QNB in the order: pancuronium ≥ vecuronium > alcuronium > SCC. Applying IC50 values to human conditions, clinical doses of these muscarinic relaxants are unlikely to exhibit any significant vagolytic action in lung tissue.