Contractility of isolated single submucosal gland from trachea

We isolated single submucosal glands from canine and feline trachea. Examination by light and electron microscope showed that these isolated glands consist mainly of glandular tissue, and no smooth muscle. Cell components in the glandular tissue were ultrastructurally normal, and myoepithelial cells surrounded acini and secretory tubules. In response to methacholine, the mucus was squeezed from the tip of the collecting ducts in coincidence with the contraction of the glands. The contractile properties of isolated single glands were examined with a force transducer. Cholinergic agents (methacholine and acetylcholine) as well as 40-150 mM K+ showed a dose-response relationship and induced tension up to 12 mg. The length-tension relationship was also observed. The removal of Ca2+ from the medium eliminated contractile response. Caffeine induced approximately 30% of the response to methacholine, and phenylephrine, a tension less than 30% of that with methacholine. These findings suggest that squeezing of mucus due to the contraction of myoepithelial cells has an important effect on secretory response of airway submucosal glands.