Regulation of murine airway surface liquid volume by CFTR and Ca2+-activated Cl- conductances.
Two Cl(-) conductances have been described in the apical membrane of both human and murine proximal airway epithelia that are thought to play predominant roles in airway hydration: (1) CFTR, which is cAMP regulated and (2) the Ca(2+)-activated Cl(-) conductance (CaCC) whose molecular identity is uncertain. In addition to second messenger regulation, cross talk between these two channels may also exist and, whereas CFTR is absent or defective in cystic fibrosis (CF) airways, CaCC is preserved, and may even be up-regulated. Increased CaCC activity in CF airways is controversial. Hence, we have investigated the effects of CFTR on CaCC activity and have also assessed the relative contributions of these two conductances to airway surface liquid (ASL) height (volume) in murine tracheal epithelia. We find that CaCC is up-regulated in intact murine CF tracheal epithelia, which leads to an increase in UTP-mediated Cl(-)/volume secretion. This up-regulation is dependent on cell polarity and is lost in nonpolarized epithelia. We find no role for an increased electrical driving force in CaCC up-regulation but do find an increased Ca(2+) signal in response to mucosal nucleotides that may contribute to the increased Cl(-)/volume secretion seen in intact epithelia. CFTR plays a critical role in maintaining ASL height under basal conditions and accordingly, ASL height is reduced in CF epithelia. In contrast, CaCC does not appear to significantly affect basal ASL height, but does appear to be important in regulating ASL height in response to released agonists (e.g., mucosal nucleotides). We conclude that both CaCC and the Ca(2+) signal are increased in CF airway epithelia, and that they contribute to acute but not basal regulation of ASL height.
Tarran
Robert
R
Cystic Fibsosis/Pulmonary Research and Treatment Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA. tarran@uclink.berkeley.edu
Loewen
Matthew E
ME
Paradiso
Anthony M
AM
Olsen
John C
JC
Gray
Micheal A
MA
Argent
Barry E
BE
Boucher
Richard C
RC
Gabriel
Sherif E
SE
D000818:Animals; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D002460:Cell Line; D018118:Chloride Channels / Q000502:physiology; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000172:deficiency / Q000502:physiology*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D020545:Respiratory Mucosa / Q000187:drug effects / Q000502:physiology*
D018118:Chloride Channels; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D002118:Calcium