Abstract
Osmotic challenge of airways alters the bioelectric properties of the airway epithelium and induces the release of factors that modulate smooth muscle tone. Recent studies in our laboratory suggested that methacholine-contracted airways relax in response to incremental increases in osmolarity, rather than from cell shrinkage or absolute solute concentration. In the present study, guinea pig tracheae were mounted in Ussing chambers to elucidate the bioelectric effects of challenge of the epithelium with hyperosmolar and isosmolar solutions. Transepithelial short-circuit current (Isc) across tracheae stimulated with basolateral methacholine was inhibited by apical amiloride, apical 5-nitro-2-(3-phenylpropylamino)benzoic acid, basolateral bumetanide, basolateral ouabain, and Cl--free solution, but not by basolateral iberiotoxin. Apical hyperosmolar challenge with NaCl variably decreased or increasedIsc, butl-mannitol (l-M) always inhibitedIsc; bumetanide attenuated decreases inIsc. The effects of the transport blockers depended upon whether Isc was initially decreased or increased. Unique concentration-dependent changes in Isc and transepithelial resistance (Rt) were observed when ionic (NaCl and KCl), nonionic impermeant (l-M and sucrose), and nonionic permeant (urea) osmolytes were added to the apical and basolateral baths. At concentrations that doubled the osmolarity of the apical bath, l-M, urea, and N-methyl-l-glucamine-gluconate (NMDG-Glu) decreased Isc. Apical isosmolar NMDG-Glu solution decreased Isc, and additional NMDG-Glu caused a further decrease in Isc. Inclusion of one permeant ion, either Na+,K+, or Cl-, reversed the response to apical isosmolar and hyperosmolar solutions. Thus, bioelectric responses of the airway epithelium to hyperosmolar solution are induced by incremental increases in osmolarity.
Footnotes
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↵1 Hypertonic solutions are those that cause cell shrinkage. Hyperosmolar solutions have osmolarity greater than that of the physiological extracellular solution. For simplicity, in this report we do not draw distinctions between the two terms when describing general phenomena.
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↵2 Apical and mucosal are terms that correspond to the intraluminal bath in perfused trachea experiments and the “air side” of the trachea. Basolateral and serosal are terms that correspond to the extraluminal bath in perfused trachea experiments and the “blood side” of the trachea.
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This work was supported, in part, by National Institutes of Health Grant 5-T32-GM07039 (to R.A.J.). Mention of brand name does not constitute product endorsement. This article is the second one of a series of four companion articles that report the effects of hyperosmolar solutions in guinea pig airways (Fedan et al., 2003a,b; Johnston et al., 2003).
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DOI: 10.1124/jpet.103.051615.
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ABBREVIATIONS:l-M,l-mannitol; EpDRF, epithelium-derived relaxing factor; MKHS, modified Krebs-Henseleit solution;Isc, short-circuit current; Rt, transepithelial resistance; SPD, spontaneous potential difference; MCh, methacholine; NMDG,N-methyl-l-glucamine; NMDG-Cl, N-methyl-l-glucamine-chloride; NMDG-Glu,N-methyl-l-glucamine-gluconate; Na-Glu, Na-gluconate; NPPB, 5-nitro-2-(3-phenylpropylamino) benzoic acid; K-Glu, K-gluconate.
- Received March 14, 2003.
- Accepted October 8, 2003.
- The American Society for Pharmacology and Experimental Therapeutics
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