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Departments of 1 Pediatrics and 3 Medicine and 2 Gregory Fleming James Cystic Fibrosis Research Center, University of Alabama at Birmingham, Birmingham, Alabama 35294-0005
ATP and its
metabolites stimulate Cl
secretion in human epithelium in vitro and in vivo. The specific
purinergic receptor subtypes that govern these effects have been
difficult to separate, in part due to multiple parallel pathways for
Cl
secretion in respiratory
and intestinal epithelia. In a simplified model using COS-7 cells, we
demonstrate acquisition of an ATP-, ADP-, AMP-, and adenosine
(ADO)-regulated halide permeability specifically following expression
of wild-type (wt) cystic fibrosis transmembrane conductance regulator
(CFTR). This halide permeability is blocked by the
P1 purinergic receptor antagonist
8-phenyl theophylline, sensitive to the protein kinase A inhibitor
H-89, and associated with a modest, dose-dependent increase in cellular
cAMP concentration. Phorbol esters poorly activate halide permeability
compared with ADO, and ADO-stimulated efflux was not affected by
treatment with the protein kinase C inhibitor bisindolylmaleimide I. The A2 ADO receptor (AR) agonists
5'-N-ethylcarboxamide adenosine
and ADO were strong activators, whereas the
A1 AR agonist
R-phenylisopropyladenosine failed to
activate halide permeability. Metabolic conversion of ADO nucleotides
by surface ecto-5'-nucleotidase to more active (less
phosphorylated) forms contributes to anion transport activation in
these cells. Immunoprecipitation with
anti-A2B AR antibody identified a
31-kDa protein in both COS-7 and human bronchial epithelial cells.
Together, these findings indicate that ADO and its nucleotides are
capable of activating wtCFTR-dependent halide permeability through
A2B AR and that this AR subtype is
present in human bronchial epithelium. We also present data showing
that this pathway can activate clinically significant mutant CFTR
molecules such as R117H.
secretion; genetics; COS-7; cystic fibrosis; G protein-coupled receptor
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