Journal of Applied Physiology, Vol 65, Issue 6 2400-2405, Copyright © 1988 by American Physiological Society
Removal of the epithelium potentiates acetylcholine in depolarizing canine bronchial smooth muscle
Y. Gao and P. M. Vanhoutte
Department of Physiology and Biophysics, Mayo Clinic, Rochester, Minnesota 55905.
Experiments were designed to determine whether the airway epithelium
affects the membrane potential of the underlying smooth muscle. The effect
of epithelium removal (by gentle rubbing) on the responsiveness of isolated
canine bronchi was studied. Simultaneous recordings of mechanical and
electrical activity were made in paired circumferential strips (with and
without epithelium) of third-order bronchi. Changes in tension were
recorded with a force transducer, and changes in membrane potential were
measured with a microelectrode. The cell membrane potential and resting
tension of the bronchial smooth muscle were stable over a 150-min period
and were not affected by removal of the epithelium. In the presence of
antagonists at muscarinic and adrenergic receptors, the resting tension and
membrane potential were comparable in preparations with and without
epithelium. By contrast, the anticholinesterase, echothiophate, caused
depolarization in bronchi without epithelium. Exposure to high potassium
induced similar levels of depolarization and contraction in tissues with
and without epithelium. No significant differences in threshold for
depolarization or for mechanical activation in the membrane
potential-tension relationship were noted in the presence or absence of
epithelium. In the presence of echothiophate, removal of the epithelium
augmented the contraction of the bronchi to acetylcholine; the
depolarization of the cell membrane induced by the cholinergic transmitter
was significantly larger than in control tissues, even when matched
contractions were compared. These observations indicate that the
respiratory epithelium generates an inhibitory substance that dampens
depolarization and contraction of bronchial smooth muscle caused by
acetylcholine.
