Mechanisms of sodium and chloride transport across equine tracheal epithelium.
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 (Isc) of 70-200 microA/cm2. Mucosal amiloride (10 microM) causes a 40-60% decrease in Isc and inhibits the net transepithelial Na flux by 95%. Substitution of Cl with gluconate resulted in a 30% decrease in basal Isc. Bicarbonate substitution with 20 mM N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid decreased the Isc by 21%. The Cl-dependent Isc 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 Isc, indicating its effect is HCO3 dependent. Addition of 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP; 100 microM) causes a 40% increase in Isc. This effect is inhibited by subsequent addition of 10 microM serosal bumetanide. Bumetanide (10 microM) reduces net Cl secretion following stimulation with 8-BrcAMP (100 microM). Serosal addition of BaCl2 (1 mM) causes a reduction in Isc equal to that following Cl replacement in the presence or absence of 100 microM 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/Cl-HCO3 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.
Tessier
G J
GJ
Department of Veterinary Biology, University of Minnesota, St Paul 55108.
Traynor
T R
TR
Kannan
M S
MS
O'Grady
S M
SM
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002034:Bumetanide / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism*; D004285:Dogs; D004847:Epithelial Cells; D004848:Epithelium / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D006736:Horses / Q000502:physiology*; D066298:In Vitro Techniques; D007700:Kinetics; D008854:Microscopy, Electron; D008954:Models, Biological; D009130:Muscle, Smooth / Q000166:cytology / Q000502:physiology; D012964:Sodium / Q000378:metabolism*; D014132:Trachea / Q000166:cytology / Q000502:physiology*
D002712:Chlorides; D002034:Bumetanide; D015124:8-Bromo Cyclic Adenosine Monophosphate; D000584:Amiloride; D012964:Sodium