Hyperosmolar Solution Effects in Guinea Pig Airways. II. Epithelial Bioelectric Responses to Relative Changes in Osmolarity

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 (I sc ) 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 Ϫ -free solution, but not by basolateral iberiotoxin. Apical hyperosmolar challenge with NaCl variably decreased or increased I sc , but D-mannitol (D-M) always inhibited I sc ; bumetanide attenuated decreases in I sc . The effects of the transport blockers depended upon whether I sc was initially decreased or increased. Unique concentrationdependent changes in I sc and transepithelial resistance (R t ) were observed when ionic (NaCl and KCl), nonionic impermeant (D-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, D-M, urea, and N-methyl-D-glucamine-gluconate (NMDG-Glu) decreased I sc . Apical isosmolar NMDG-Glu solution decreased I sc , and additional NMDG-Glu caused a further decrease in I sc . Inclusion of one permeant ion, either Na

Hyperosmolar Solution Effects in Guinea Pig Airways. III. Studies on the Identity of Epithelium-Derived Relaxing Factor in Isolated Perfused Trachea Using Pharmacological Agents

“…Previous experiments have suggested Wu et al, 2003) that EpDRF is released in response to incremental changes in osmolarity as opposed to absolute osmolarity of solutions bathing the epithelium. Furthermore, the release of EpDRF is associated with changes in bioelectric activity of the epithelium (Dortch-Carnes et al, 1999;Wu et al, 2003). In the present study, a panel of agents were examined for their effects on relaxation responses to hyperosmolar solution, to gain insight into the identity of EpDRF.…”

“…Mention of brand name does not constitute product endorsement. This article is the third one of a series of four companion articles that report the effects of hyperosmolar solutions in guinea pig airways Wu et al, 2003 1999; , although an inhibitory effect of hemoglobin but not of methylene blue or inhibitors of nitricoxide synthase suggested that EpDRF release by hyperosmolar solution has features resembling nitric oxide (Munakata et al, 1990;Fedan et al, 1999). It is not known whether the EpDRF released by contractile agonists in the coaxial bioassay preparation, and that released by hyperosmolar solution in the perfused trachea, are the same substance.…”

“…It has been suggested that the epithelium may release two substances, one to which vascular smooth muscle is sensitive and the other to which airway smooth muscle is sensitive (Fedan et al, 1990). Previous experiments have suggested Wu et al, 2003) that EpDRF is released in response to incremental changes in osmolarity as opposed to absolute osmolarity of solutions bathing the epithelium. Furthermore, the release of EpDRF is associated with changes in bioelectric activity of the epithelium (Dortch-Carnes et al, 1999;Wu et al, 2003).…”

“…Cell volume changes and the resulting compensatory changes in ion transport activity (Rehn et al, 1998) involve the cellular cytoskeleton (Lang et al, 1998). Inasmuch as the relaxant and bioelectric responses to hyperosmolarity are affected by inhibition of ion transport Wu et al, 2003), we examined the effects of cytoskeleton disruptors. Erythro-9-(2-hydroxyl-3-nonyl)adenine, a cytoskeleton inhibitor that also inhibits phosphodiesterase II and adenosine deaminase, inhibited the contraction to MCh but had no effect on relaxation to D-M.…”

Hyperosmolar Solution Effects in Guinea Pig Airways. IV. Lipopolysaccharide-Induced Alterations in Airway Reactivity and Epithelial Bioelectric Responses to Methacholine and Hyperosmolarity

“…Mention of brand name does not constitute product endorsement. This article is the fourth one of a series of four companion articles that report the effects of hyperosmolar solutions in guinea pig airways (Fedan et al, 2003a,b;Wu et al, 2003).…”