Effect of Ciprofloxacin on Contractile Responses of Canine Airway Smooth Muscle

Abstract

To elucidate whether the new quinolone ciprofloxacin affects cholinergic neuro-effector transmission in the airway, we studied canine isolated bronchial segments under isometric conditions in vitro. Intrapulmonary lobar or segmental bronchi were suspended in the organ chambers filled with Krebs-Henseleit solution, and the isometric tension was continuously recorded by a force-displacement transducer.Addition of ciprofloxacin (2 × 10^-3 M) attenuated the contractile responses to electrical field stimulation (EFS), so that the stimulus frequency required to produce a half-maximal contraction (ES₅₀) increased from 1.2 ± 0.2 to 1.5 ± 0.2 Hz (p<0.05), whereas it was without effect on those to exogenously administered acetylcholine.The decrease in the EFS-induced contraction produced by ciprofloxacin was concentration-dependent and was not influenced by propranolol or tetraethylammonium, but partially inhibited by ouabain.These results suggest that ciprofloxacin may inhibit cholinergic neuro-effector transmission in the airway smooth muscle by inhibiting the exocytotic release of acetylcholine, probably involving the stimulation of Na⁺-K⁺-ATPase and concomitant repolarization/hyperpolarization of cholinergic nerve terminals.