Mechanisms of sodium and chloride transport across equine tracheal epithelium

G. J. Tessier, T. R. Traynor, M. S. Kannan, S. M. O'Grady

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Equine tracheal epithelium, stripped of serosal muscle, mounted in Ussing chambers, and bathed in plasmalike Ringer solution generates a serosa-positive transepithelial potential of 10-22 mV and a short-circuit current (I(sc)) of 70-200 μA/cm2. Mucosal amiloride (10 μM) causes a 40-60% decrease in I(sc) and inhibits the net transepithelial Na flux by 95%. Substitution of CI with gluconate resulted in a 30% decrease in basal I(sc). Bicarbonate substitution with 20 mM N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid decreased the I(sc) by 21%. The Cl-dependent I(sc) was inhibited by serosal addition of 1 mM amiloride. Bicarbonate replacement or serosal amiloride (1 mM) inhibits the net Cl flux by 72 and 69%, respectively. Bicarbonate replacement significantly reduces the effects of serosal amiloride (1 mM) on I(sc), indicating its effect is HCO3 dependent. Addition of 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP; 100 μM) causes a 40% increase in I(sc). This effect is inhibited by subsequent addition of 10 μM serosal bumetanide. Bumetanide (10 μM) reduces net Cl secretion following stimulation with 8-BrcAMP (100 μM). Serosal addition of BaCl2 (1 mM) causes a reduction in I(sc) equal to that following Cl replacement in the presence or absence of 100 μM cAMP. These results suggest that 1) Na absorption depends on amiloride inhibitable Na channels in the apical membrane, 2) Cl influx across the basolateral membrane occurs by both a Na-H/ClHCO3 parallel exchange mechanism under basal conditions and by a bumetanide-sensitive Na-(K?)-Cl cotransport system under cAMP-stimulated conditions, and 3) basal and cAMP-stimulated Cl secretion depends on Ba-sensitive K channels in the basolateral membrane.

Original languageEnglish (US)
Pages (from-to)L459-L467
JournalAmerican Journal of Physiology - Lung Cellular and Molecular Physiology
Issue number6 3-3
StatePublished - 1990


  • amiloride
  • bumetanide
  • chloride secretion
  • ion transport
  • sodium chloride cotransport
  • sodium-proton/chloride-bicarbonate exchanger


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