Increased responsiveness to 5-hydroxytryptamine after antigenic challenge is inhibited by nifedipine and niflumic acid in rat trachea in vitro

Summary 1. Antigenic challenge often induces hyperreactivity in asthmatic airway, although the precise mechanism(s) underlying this increased responsiveness is not entirely known. 2. Tracheae obtained from ovalbumin (OVA)‐sensitized saline‐ or OVA‐challenged rats were placed in 10 mL bath chambers for isometric recording of 5‐hydroxytryptamine (5‐HT)‐induced contractions. 3. 5‐Hydroxytryptamine induced a stronger contraction compared with control in antigen‐challenged trachea under normal or Ca2+‐free conditions. 4. In tracheae pretreated with the L‐type Ca2+ channel blocker nifedipine (10−6 mol/L) or the Ca2+‐activated Cl– channel blocker niflumic acid (10−4 mol/L), this hyperresponsiveness was not developed in either normal or Ca2+‐free medium. 5. The increased contractile response to 5‐HT in allergic rat isolated trachea may be related to a greater ionic (Ca2+ and Cl–) channel involvement.