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

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Abstract
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.

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