Effect of cromakalim on bronchoconstriction evoked by cholinergic nerve stimulation in guinea-pig isolated trachea

1. Cromakalim reduced intraluminal pressure in the guinea-pig isolated, innervated trachea. 2. Preganglionic stimulation of the cervical vagus nerve elicited a frequency-dependent increase in intraluminal pressure. Cromakalim attenuated responses to vagal stimulation in a concentration-dependent manner at all frequencies tested. 3. Field stimulation caused a frequency-dependent increase in intraluminal pressure mediated by muscarinic cholinoceptors. Cromakalim did not affect the amplitude of responses at any frequency of stimulation, even at high concentrations. 4. Acetylcholine, added to the Krebs solution bathing the adventitial surface of the trachea, evoked a concentration-dependent increase in intraluminal pressure. The concentration-effect curve for acetylcholine was unaltered in the presence of cromakalim. 5. It is concluded that cromakalim modulates cholinergic neuroeffector transmission in the trachea chiefly by a prejunctional mechanism. However, cromakalim probably does not interfere with acetylcholine release from postganglionic cholinergic neurones.