Calcium uptake into guinea-pig trachealis: the effect of epithelium removal

Removal of the epithelium from preparations of guinea-pig airways in vitro increases the responsiveness of the smooth muscle of normal and ovalbumin-sensitized animals to a number of contractile agents. To determine if epithelium removal results in an increase in Ca2+ entry into the smooth muscle, the effect of removing the epithelium on Ca2+ uptake into the trachealis smooth muscle was studied using a modified La3+-technique. KCl increased Ca2+ uptake in the presence and absence of the epithelium in control and sensitized animals. Methacholine did not promote Ca2+ uptake, whether or not the epithelium was present, in either control or sensitized animals. Ovalbumin did not stimulate Ca2+ uptake into the trachealis of sensitized animals. These results indicate that the increase in responsiveness of airway smooth muscle seen on epithelium removal is not a consequence of a facilitation of Ca2+ entry into the muscle. The increased responsiveness to methacholine in control animals, and to ovalbumin in preparations in tension studies in epithelium-free tissues from sensitized animals, cannot be explained by an increased availability of extracellular Ca2+ into the muscle, but, rather may reflect some other effect of the epithelium-derived modulatory factor.