Apical and basolateral ATP stimulates tracheal epithelial chloride secretion via multiple purinergic receptors.
Stimulation of Cl- secretion across the airway epithelium by ATP or UTP as agonists has therapeutic implications for cystic fibrosis. Our results demonstrate that ATP stimulates Cl- secretion in rat tracheal epithelial cell monolayers in primary culture from the apical or basolateral side of the monolayer. Multiple types of ATP-sensitive Cl- conductances in intact monolayers were elucidated through inhibition by Cl- channel-blocking drugs. Multiple Cl- conductances stimulated by ATP and adenosine 3',5'-cyclic monophosphate (cAMP) (tested for comparison) were also deciphered more specifically by nystatin permeabilization of the basolateral membrane, subsequent imposition of symmetrical Cl-, I-, or Br- solutions to test halide permselectivity, inhibition by Cl- channel-blocking drugs, and construction of current-voltage plots to study time and voltage dependence of the currents. Apical ATP stimulates Cl- secretion through P2U (or P2Y2) purinergic receptors via both intracellular Ca2+ (Ca(2+)i)-dependent and Cai(2+)-independent signaling pathways by opening outwardly rectifying Cl- channels (ORCCs), cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channels, and Cai(2+)-dependent Cl- channels. Basolateral ATP stimulates Cl- secretion via a combination of receptor subtypes (P2T and P2U) or a novel type of receptor (P2Y3), independent of Cai2+ or cAMP signaling by opening only CFTR channels. cAMP also stimulated multiple types of Cl- conductances, consistent with simultaneous activation of CFTR and ORCCs. Together, these results suggest that ATP as an agonist stimulates Cl- secretion via multiple purinergic receptors and multiple signal transduction pathways activated in different membrane domains of tracheal epithelia.
Hwang
T H
TH
Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Schwiebert
E M
EM
Guggino
W B
WB
D000255:Adenosine Triphosphate / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D018118:Chloride Channels / Q000037:antagonists & inhibitors; D002712:Chlorides / Q000378:metabolism* / Q000502:physiology; D000242:Cyclic AMP / Q000502:physiology; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism; D004553:Electric Conductivity; D004847:Epithelial Cells; D004848:Epithelium / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D011983:Receptors, Purinergic / Q000378:metabolism*; D015398:Signal Transduction; D014132:Trachea / Q000166:cytology / Q000378:metabolism*
D018118:Chloride Channels; D002712:Chlorides; D011983:Receptors, Purinergic; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D002118:Calcium