AJP - Lung Cellular and Molecular Physiology, Vol 268, Issue 3 526-L531, Copyright © 1995 by American Physiological Society
Chloride secretion across distal airway epithelium: relationship to submucosal gland distribution
S. T. Ballard, J. D. Fountain, S. K. Inglis, M. R. Corboz and A. E. Taylor
Department of Physiology, College of Medicine, University of South Alabama, Mobile 36688.
To evaluate the possible relationship between submucosal glands and
transepithelial Cl- secretion, we compared the bioelectric properties of
two distal airway regions: bronchioles, which contain few submucosal
glands, and small bronchi, which contain numerous glands. Intact distal
bronchi were dissected from the lungs of 4-8 wk old pigs and cannulated
with micropipettes and perfused. Transepithelial potential difference (PD),
short-circuit current (Isc), and barrier resistance (Rm) in distal bronchi,
determined by cable analysis, were -3.0 +/- 0.4 mV, 50.7 +/- 5.9
microA/cm2, and 59.6 +/- 5.9 omega.cm2, respectively (means +/- SE).
Bumetanide (10 microM), which blocks Cl- secretion through inhibition of
Na(+)-K(+)-2Cl- cotransport, reduced Isc in distal bronchi by 30.0 +/- 5.5
microA/cm2 (59.0% of the total Isc). By comparison, a previous study of
porcine distal airways [S.T. Ballard and A.E. Taylor, Am. J. Physiol. 267
(Lung Cell. Mol. Physiol. 11): L79-L84, 1994] determined that
bumetamide-sensitive Isc in bronchioles was 2.6 +/- 1.4 microA/cm2 (only
9.0% of the total Isc). Submucosal gland duct openings to the luminal
surface were identified microscopically and counted in representative
fields. In eight bronchioles, 6.8 +/- 4.4 gland duct openings/cm2 of airway
surface were observed, whereas seven distal bronchi contained 916.8 +/-
84.0 gland duct openings/cm2, over a 100-fold difference. These data
suggest that a direct relationship may exist between the magnitude of
active transepithelial Cl- secretion and the presence of submucosal glands
in normal distal airways.
