Airway hyperresponsiveness induced by repeated esophageal infusion of HCl in guinea pigs

Gastroesophageal reflux is a common disorder closely related to chronic airway diseases, such as chronic cough, asthma, chronic bronchitis, and chronic obstructive disease. Indeed, gastroesophageal acid reflux into the respiratory tract causes bronchoconstriction, but the underlying mechanisms have still not been clarified. This study aimed to elucidate functional changes of bronchial smooth muscles (BSMs) isolated from guinea pigs in an animal model of gastroesophageal reflux. The marked airway inflammation, hyperresponsiveness and remodeling were observed after guinea pigs were exposed to intraesophageal HCl infusion for 14 days. In addition, contractile responses to acetylcholine (ACh), KCl, electrical field stimulation, and extracellular Ca²⁺ were greater in guinea pigs infused with HCl compared with control groups. The L-type voltage-dependent Ca²⁺ channels (L-VDCC) blocker, nicardipine, significantly inhibited ACh-and Ca²⁺-enhanced BSM contractions in guinea pigs infused with HCl. The Rho-kinase inhibitor, Y27632, attenuated ACh-enhanced BSM contractions in guinea pigs infused with HCl. Moreover, mRNA and protein expressions for muscarinic M₂ and M₃ receptors, RhoA, and L-VDCC in BSM were detected by real-time PCR and Western blot. Expressions of mRNA and protein for muscarinic M3 receptors, RhoA, and L-VDCC were greater than in BSM of HCl-infused guinea pigs, whereas levels of muscarinic M₂ receptors were unchanged. We demonstrate that acid infusion to the lower esophagus and, subsequently, microaspiration into the respiratory tract in guinea pigs leads to airway hyperresponsiveness and overactive BSM. Functional and molecular results indicate that overactive BSM is the reason for enhancement of extracellular Ca²⁺ influx via L-VDCC and Ca²⁺ sensitization through Rho-kinase signaling.