title: A novel role for cyclic nucleotide-gated cation channels in lung liquid homeostasis in sheep.
abstract: 1. Sheep lungs were artificially perfused in situ with warmed whole oxygenated sheep blood. The airspaces of the lungs were filled with liquid containing an impermeant tracer, to allow measurement of the rate of net transepithelial liquid movement under various conditions. 2. Dichlorobenzamil (1.5 x 10-5 M), a blocker of cyclic nucleotide-gated cation channels, inhibited the resting absorption of lung liquid in sheep aged 6 months (n = 5) (from -36.47 +/- 4.62 to -4.36 +/- 5.27 ml h-1, means +/- s.e.m.; P < 0.005, paired t test). Amiloride (10-4 M), a blocker of epithelial sodium channels, had no additive effect to that of dichlorobenzamil. 3. In the lungs of sheep aged 6 months (n = 4), amiloride (10-4 M) partially inhibited the resting absorption of liquid (from -35.21 +/- 8.57 to -11.05 +/- 4.91 ml h-1; P < 0.05, one-tailed paired t test), and dichlorobenzamil (1.5 x 10-5 M) exerted an additive effect to that of amiloride resulting in secretion at +6.29 +/- 3.05 ml h-1 (P < 0. 01, paired t test). 4. In the lungs of sheep aged 6 weeks (n = 3), amiloride (10-4 M) also inhibited the resting absorption of liquid (from -26.36 +/- 14.05 to -5.17 +/- 8.27 ml h-1; P < 0.05, one-tailed paired t test); however, dichlorobenzamil (1.5 x 10-5 M) did not exert an additive effect to that of amiloride. 5. In the lungs of sheep aged 6 months (n = 4), amiloride (10-4 M) partially inhibited the resting absorption of liquid (from -35.70 +/- 8.58 to -6.79 +/- 4.28 ml h-1; P < 0.05, paired t test), and pimozide (1.5 x 10-4 M), another blocker of cyclic nucleotide-gated cation channels, also exerted an additive effect to that of amiloride, resulting in secretion of lung liquid at +15.36 +/- 9.14 ml h-1 (P < 0.05, paired t test). 6. We conclude that cyclic nucleotide-gated cation channels mediate a component of lung liquid absorption in sheep aged 6 months (but not in sheep aged 6 weeks), and that a mechanism for lung liquid secretion (present in fetuses) is retained at 6 months of age.
authors.affiliation: Department of Child Health, St George's Hospital Medical School, London SW17 0RE, UK. sgms369@sghms.ac.uk
authors.forename: R W
authors.initials: RW
authors.lastname: Junor
authors.forename: A R
authors.initials: AR
authors.lastname: Benjamin
authors.forename: D
authors.initials: D
authors.lastname: Alexandrou
authors.forename: S E
authors.initials: SE
authors.lastname: Guggino
authors.forename: D V
authors.initials: DV
authors.lastname: Walters
mesh_terms: D000042:Absorption; D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D001826:Body Fluids / Q000187:drug effects / Q000502:physiology*; D004232:Diuretics / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000494:pharmacology; D006706:Homeostasis / Q000187:drug effects / Q000502:physiology; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D007473:Ion Channels / Q000037:antagonists & inhibitors / Q000502:physiology*; D008168:Lung / Q000502:physiology*; D009712:Nucleotides, Cyclic / Q000502:physiology*; D009997:Osmotic Pressure; D010868:Pimozide / Q000494:pharmacology; D012756:Sheep; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology
chemical_list: D004232:Diuretics; D018492:Dopamine Antagonists; D007473:Ion Channels; D009712:Nucleotides, Cyclic; D015222:Sodium Channels; C041470:3',4'-dichlorobenzamil; D010868:Pimozide; D000584:Amiloride