title: Sustained calcium entry through P2X nucleotide receptor channels in human airway epithelial cells.
abstract: Purinergic receptor stimulation has potential therapeutic effects for cystic fibrosis (CF). Thus, we explored roles for P2Y and P2X receptors in stably increasing [Ca(2+)](i) in human CF (IB3-1) and non-CF (16HBE14o(-)) airway epithelial cells. Cytosolic Ca(2+) was measured by fluorospectrometry using the fluorescent dye Fura-2/AM. Expression of P2X receptor (P2XR) subtypes was assessed by immunoblotting and biotinylation. In IB3-1 cells, ATP and other P2Y agonists caused only a transient increase in [Ca(2+)](i) derived from intracellular stores in a Na(+)-rich environment. In contrast, ATP induced an increase in [Ca(2+)](i) that had transient and sustained components in a Na(+)-free medium; the sustained plateau was potentiated by zinc or increasing extracellular pH. Benzoyl-benzoyl-ATP, a P2XR-selective agonist, increased [Ca(2+)](i) only in Na(+)-free medium, suggesting competition between Na(+) and Ca(2+) through P2XRs. Biochemical evidence showed that the P2X(4) receptor is the major subtype shared by these airway epithelial cells. A role for store-operated Ca(2+) channels, voltage-dependent Ca(2+) channels, or Na(+)/Ca(2+) exchanger in the ATP-induced sustained Ca(2+) signal was ruled out. In conclusion, these data show that epithelial P2X(4) receptors serve as ATP-gated calcium entry channels that induce a sustained increase in [Ca(2+)](i). In airway epithelia, a P2XR-mediated Ca(2+) signal may have therapeutic benefit for CF.
authors.affiliation: Department of Physiology and Biophysics, and the Gregory Fleming James Cystic Fibrosis Research Center, University of Alabama, Birmingham, Alabama 35294-0005, USA. zsembery@physiology.uab.edu
authors.forename: Akos
authors.initials: A
authors.lastname: Zsembery
authors.forename: Amanda T
authors.initials: AT
authors.lastname: Boyce
authors.forename: Lihua
authors.initials: L
authors.lastname: Liang
authors.forename: János
authors.initials: J
authors.lastname: Peti-Peterdi
authors.forename: P Darwin
authors.initials: PD
authors.lastname: Bell
authors.forename: Erik M
authors.initials: EM
authors.lastname: Schwiebert
mesh_terms: D000244:Adenosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology; D002460:Cell Line; D003600:Cytosol / Q000378:metabolism; D005456:Fluorescent Dyes; D006801:Humans; D007700:Kinetics; D008856:Microscopy, Fluorescence; D018048:Receptors, Purinergic P2 / Q000187:drug effects / Q000502:physiology*; D058469:Receptors, Purinergic P2X; D020545:Respiratory Mucosa / Q000502:physiology*; D014544:Uridine Triphosphate / Q000494:pharmacology
chemical_list: D015220:Calcium Channels; D005456:Fluorescent Dyes; D018048:Receptors, Purinergic P2; D058469:Receptors, Purinergic P2X; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D002118:Calcium; D014544:Uridine Triphosphate