CHLORIDE SECRETION ACROSS DISTAL AIRWAY EPITHELIUM - RELATIONSHIP TO SUBMUCOSAL GLAND DISTRIBUTION

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 (I-sc), and barrier resistance (R(m)) in distal bronchi, determined by cable analysis, were -3.0 +/- 0.4 mV, 50.7 +/- 5.9 mu A/cm(2), and 59.6 +/- 5.9 Omega . cm(2), respectively (means +/- SE). Bumetanide (10 mu M), which blocks Cl- secretion through inhibition of Na+-K+-2Cl(-) cotransport, reduced I-sc in distal bronchi by 30.0 +/- 5.5 mu A/cm(2) (59.0% of the total I-sc). 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 bumetanide-sensitive I-sc in bronchioles was 2.6 +/- 1.4 mu A/cm(2) (only 9.0% of the total I-sc). 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/cm(2) of airway surface were observed, whereas seven distal bronchi contained 916.8 +/- 84.0 gland duct openings/cm(2), 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.