Activation of an apical Cl- conductance by Ca2+ ionophores in cystic fibrosis airway epithelia.
Cystic fibrosis (CF) airway epithelia express a defect in adenosine 3',5'-cyclic monophosphate (cAMP)-dependent regulation of apical membrane Cl- channels. Recent patch-clamp studies have raised the possibility that Ca2+ -dependent mechanisms for the activation of Cl- secretion may be preserved in CF airway epithelia. To determine 1) whether intact normal (N1) and CF airway epithelia exhibit a Ca2+ -dependent mechanism for activation of Cl- secretion and 2) whether Ca2+ -dependent mechanism for activation of Cl- secretion and 2) whether Ca2+ -dependent mechanisms initiate Cl- secretion via activation of an apical membrane Cl- conductance (GCl-), nasal epithelia from N1 and CF subjects were cultured on collagen membranes, and responses to isoproterenol or Ca2- ionophores [A23187 10(-6) M; ionomycin (10(-5)M)] were measured with transepithelial and intracellular techniques. Isoproterenol induced activation of an apical membrane GCl- in N1 cultures but was ineffective in CF. In contrast, in both N1 and CF amiloride-pretreated cultures, A23187 induced an increase in the equivalent short-circuit current that was associated with an activation of an apical membrane Gc1- and was bumetanide inhibitable. A23187 addition during superfusion of the lumen with a low Cl- (3 mM) solution reduced intracellular Cl- activity of CF cells. A Ca2+ ionophore of different selectivity properties, ionomycin, was also an effective Cl- secretagogue in both N1 and CF cultures. We conclude that 1) the A23187 induced Cl- secretion via activation of an apical GCl- in N1 human nasal epithelium, and 2) in contrast to an isoproterenol-dependent path, a Ca2+ -dependent path for GCl- activation is preserved in CF epithelia.
Willumsen
N J
NJ
Department of Medicine, University of North Carolina, Chapel Hill 27514.
Boucher
R C
RC
D000293:Adolescent; D000328:Adult; D000584:Amiloride / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology*; D002118:Calcium / Q000502:physiology; D002478:Cells, Cultured; D018118:Chloride Channels; D002712:Chlorides / Q000502:physiology*; D003550:Cystic Fibrosis / Q000503:physiopathology*; D004553:Electric Conductivity; D004987:Ethers / Q000494:pharmacology; D005260:Female; D006801:Humans; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D015759:Ionomycin; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008565:Membrane Proteins / Q000502:physiology*; D009298:Nasal Polyps / Q000503:physiopathology; D012016:Reference Values; D014420:Turbinates / Q000503:physiopathology*
D018118:Chloride Channels; D002712:Chlorides; D004987:Ethers; D007473:Ion Channels; D008565:Membrane Proteins; D000001:Calcimycin; D015759:Ionomycin; D000584:Amiloride; D007545:Isoproterenol; D002118:Calcium