Paths of ion transport across canine fetal tracheal epithelium.
Fluid secretion by the fetal sheep lung is thought to be driven by secretion of Cl- by the pulmonary epithelium. We previously demonstrated Cl- secretion by tracheal epithelium excised from fetal dogs and sheep. In this study we characterized the ion transport pathways across fetal canine tracheal epithelium. The transport of Na+ and Cl- across trachea excised from fetal dogs was evaluated from transepithelial electrical properties and isotope fluxes. Under basal conditions the tissues were characterized by a lumen-negative potential difference (PD) of 11 mV and conductance of 5.2 mS/cm2. The short-circuit current (Isc) was 43 microA/cm2 (1.6 mueq.cm-2.h-1). Basal Na+ flows were symmetrical, but net Na+ absorption (1.1 mueq.cm-2.h-1) could be induced by exposure of the luminal surface to amphotericin B (10(-6) M). Bilateral replacement of Na+ reduced Isc by 85%. Replacement of submucosal Na+ or exposure to submucosal furosemide (10(-4) M) reduced net Cl- secretion by 60-70%. Luminal exposure to indomethacin (10(-6) M) induced a 50% decrease in Isc, whereas isoproterenol (10(-6) M) increased Isc by 120%. The properties of the Cl- secretory pathway across fetal dog trachea are consistent with the model proposed for Cl- secretion across adult dog trachea and other Cl- -secreting tissues (e.g., bullfrog cornea and shark rectal gland). The absence of basal Na+ absorption by fetal dog trachea probably reflects limited apical membrane Na+ permeability.
Cotton
C U
CU
Department of Medicine, School of Medicine, University of North Carolina, Chapel Hill 27514.
Boucher
R C
RC
Gatzy
J T
JT
D000666:Amphotericin B / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002712:Chlorides / Q000378:metabolism*; D004285:Dogs; D004848:Epithelium / Q000378:metabolism; D005333:Fetus / Q000378:metabolism; D005665:Furosemide / Q000494:pharmacology; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism*; D014132:Trachea / Q000187:drug effects / Q000378:metabolism*
D002712:Chlorides; D005665:Furosemide; D000666:Amphotericin B; D012964:Sodium; D007545:Isoproterenol; D007213:Indomethacin