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Vol. 289, Issue 2, 911-917, May 1999
Pathology and Physiology Research Branch, Health Effects Laboratory
Division, National Institute for Occupational Safety and Health,
Morgantown, West Virginia (J.D-C., J.S.F.); and
Department of
Physiology, East Carolina University, Greenville, North Carolina
(M.R.V.S.)
The relationship between epithelial bioelectric events and
epithelium-dependent relaxant and contractile responses of airway smooth muscle in response to hyperosmolar and hypo-osmolar solutions was investigated in guinea pig isolated trachea. Tracheae were perfused
with normal or nonisosmotic modified Krebs-Henseleit solution while
simultaneously monitoring transepithelial potential difference
(VT) and contractile and relaxant responses of the muscle.
Baseline VT was
10.1 to
13.3 mV (distal and proximal ends, respectively). Intraluminal amiloride (10
4 M)
induced a 3.7-mV depolarization, verifying that the VT was of epithelial origin. Extraluminal methacholine (3 × 10
7 M; EC50) caused hyperpolarization and
smooth muscle contraction; intraluminal methacholine had very little
effect. Increasing intraluminal bath osmolarity via addition of 240 mOsM NaCl or KCl caused an immediate and prolonged depolarization and
epithelium-dependent relaxation. Increasing intraluminal bath
osmolarity with sucrose evoked similar responses, except that an
immediate, transient hyperpolarization and contraction preceded the
depolarization and relaxation. Increasing extraluminal bath osmolarity
with 240 mOsM NaCl induced depolarization and a longer lasting
epithelium-dependent relaxation, whereas extraluminally added 240 mOsM
KCl induced a complex smooth muscle response (i.e., transient
relaxation followed by contraction), which was accompanied by prolonged
depolarization. Intraluminal hypo-osmolarity produced a transient
hyperpolarization followed by depolarization along with contraction of
the smooth muscle. Bioelectric responses always preceded smooth muscle
responses. These results suggest that bioelectric events in the
epithelium triggered by nonisosmotic solutions are associated with
epithelium-dependent responses in tracheal smooth muscle.
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