Role of acetylcholinesterase in airway epithelium-mediated inhibition of acetylcholine-induced contraction of guinea-pig isolated trachea

Abstract

To seek evidence for the involvement of acetylcholinesterase activity in the modulatory influence of the airway epithelium, we examined responses to acctylcholine (ACh), hcthancchol, histamine or KCI in isolated epithelium-intact and epithelium-denuded guinea-pig trachcalis preparations. The concentration-response curves to ACh were shifted 26-fold to the left by epithelial denudation hut the contractile response to KCl was not altered. The response to histamine in epithelium-denuded preparations increased 4-fold with no attenuation in the presence of physostigmine (30 nM). Physostigmine (30 nM) potentiated the response to ACh in epithelium-intact tissues more (about 26-fold) than in epithelium-denuded tissues (about 3.5-fold). Thus, in the presence of physostigmine removing the epithelium had only a slight effect (not statistically significant) on the potency of ACh to contract the trachea. Removing the epithelium had no effect on the potency of bethanechol, a muscarinic receptor agonist that is not a substrate for cholincsicrases. Physostigmine itself contracted the trachealis muscle but the pD 2 values and maximum responses in epithelium-intact and denuded preparations were not significantly different. The frequency-response curves to electrical field-stimulated cholinergic contractions were unaffected by removing the epithelium. In conclusion, the principal mechanism by which the epithelium inhibis contraction of guinea-pig trachea to exogenously applied ACh is via epithelium-derived acetylcholinesterase activity.