Nonneural components in the response of fresh human airways to electric field stimulation

Abstract

Fresh human bronchi, obtained at thoracotomy and maintained at 37 degrees C, were studied in vitro to investigate their response to electric field stimulation (EFS). We found complex responses that were not only composed of a rapid initial nerve-mediated cholinergic contraction and a non-adrenergic nerve-mediated relaxation, but, in 80% of preparations, also of a tonic contraction with a sustained time course. This sustained phase was not blocked by the nervous conductance blocker tetrodotoxin (TTX) and was therefore not neurally mediated. Controlled transient cooling to 4 degrees C in the organ bath reduced this sustained phase selectively for several hours. The leukotriene (LT) antagonist FPL 55712, dexamethasone, which inhibits phospholipase A2, and the antiasthmatic drug cromolyn all reduced the sustained phase significantly. In 20% of strips, an additional TTX-resistant contraction was seen directly after the cholinergic phase. This contraction could be inhibited by indomethacin. A similar small peak sometimes appeared after selective blocking of either the cholinergic or the sustained phases. Experiments in which the epithelium was removed from the strips suggested that this indomethacin-sensitive response, but not the sustained phase, was dependent on the presence of epithelium. These results show that EFS of fresh human bronchi stimulated cholinergic and nonadrenergic inhibitory nerves and gave rise to a partly epithelium-dependent synthesis of arachidonic acid metabolites, which caused contractile responses that interfered with the neurally mediated responses.