[Effect of ciprofloxacin on contractile responses of canine airway smooth muscle].

To elucidate whether the new quinolone ciprofloxacin affects cholinergic neuto-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 x 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.