Acetylcholine-Induced Smooth Muscle Contraction of Intrapulmonary Small Bronchi Is Augmented in Antigen-Induced Airway Hyperresponsive Rats

Abstract

Smooth muscle responsiveness of intrapulmonary small bronchi obtained from repeatedly antigen−challenged rats was compared with that from control animals to determine whether smooth muscle contractility of peripheral airways is augmented by such repeated challenge.In intact(non−permeabilized)smooth muscles of intrapulmonary bronchi, the acetylcholine(ACh)−induced contractile response was significantly augmented in the repeated challenge group, although 60−mM K⁺−induced contraction was within the normal level.In β−escin−permeabilized muscles, no significant difference between groups was observed in the Ca²⁺−induced contractile responses.Thus, augmented ACh−induced contraction of intact intrapulmonary small bronchial smooth muscle might be, at least in part, due to an enhanced ACh−mediated Ca²⁺−sensitizing signal.