Epithelium removal increases the reactivity of human isolated tracheal muscle to methacholine and reduces the effect of verapamil.

Removal of the epithelium increased the sensitivity of human isolated tracheal smooth muscle to methacholine, producing a greater than 2-fold leftward shift in the concentration-response curve. Concomitantly, the ability of verpamil to lower the maximum contractile response was reduced in tissues without an intact epithelium. These findings suggest a role for the epithelium in modulating the reactivity of human and extend the findings of similar studies in experimental animals.