M J Stutts — Page 4 | PubMed Health

PubMed1981

Regional differences in bioelectric properties and ion flow in excised canine airways.

Absorption of airway liquid, as it moves from the large surface area of distal airways to more central airway surfaces, is considered to be essential for regulation of the depth of airway liquid. The short-circuited excised canine trachea, however, secretes Cl- and absorbs a lesser amount of Na+. We compared bioelectric properties and unidirectional ion flows across epithelia excised from trachea and mainstem and 4th- to 6th-generation bronchi. Compared with trachea, 4th- to 6th-generation bronchi exhibited a lower potential difference (8.9 compared with 35 mV) and higher direct-current conductance (6.9 compared with 2.1 mS . cm-2). Corresponding values for main-stem bronchus were intermediate. Under short-circuit conditions, the trachea secreted Cl- (1.75 mueq . cm-2 . h-1) and absorbed Na+ (1.15 mueq . cm-2 . h-1). K+ fluxes were symmetric. Main-stem bronchus exhibited a similar pattern of ion flow. Subsegmental bronchi absorbed 2.0 mueq Na+ . cm-2 . h-1 and secreted 0.04 mueq K+ . cm-2 . h-1, but net Cl- transport was absent. Under open circuit, Na+ absorption persisted in all regions, but net Cl- secretion disappeared in the trachea and main-stem bronchi. Na+ absorption was uniformly abolished by addition of ouabain (3 x 10(-5) M) to the submucosal bath. We conclude that NaCl absorption dominates resting ion translocation in canine bronchi and that liquid absorption probably occurs at these sites in vivo.

Animals↗

PubMed1980

Chemical modulation of alveolar epithelial permeability.

The volume and composition of fluid on the surface of the alveoli can affect alveolar ventilation, gas diffusion, and macrophage function. The passive permeability and active processes of the alveolar epithelial lining play a role in regulating surface fluid and are a potential site of damage by airborne chemicals. Like other epithelial barriers, the alveolar lining is permeable to lipophilic substances but restricts the transmural flow of small ions and hydrophilic nonelectrolytes (equivalent pore radius ca. 0.5-1.5 nm). The mammalian fetal lung and alveolar sacs of the adult bullfrog secrete Cl- and K+ into the airspace. Secretion by the fetal lung ceases at birth. Many environmental agents increase the permeability of the capillary endothelium and/or respiratory epithelium and induce pulmonary edema. Studies with bullfrog alveolar sacs have demonstrated that selective effects may or may not be followed by general derangement of the epithelial barrier. Exposure of the luminal surface to HgCl2 (10(-6) to 10(-4) M) induces a selective increase in Cl- secretion that is followed by a fall in transport and a general increase in ion permeation. CdCl2 (10(-5) to 10(-3) M) depresses ciliomotion on cells on the trabecula of the alveolus but does not affect Cl- secretion or transepithelial conductance. HNO3, like other mineral acids, increases conductance and the radii or pores in the barrier, whereas NaNO3 selectively inhibits Cl- secretion. Amphotericin B(10(7) to 10(-5) MJ) induces K+ secretion into the lumen of both bullfrog and rat lung. We conclude that environmental agents induce changes in epithelial function that may compromise the lung's ability to regulate respiratory fluid without destroying the characteristic permeability of the epithelial lining.

Air Pollutants↗