Sustained calcium entry through P2X nucleotide receptor channels in human airway epithelial cells.
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.
Zsembery
Akos
A
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
Boyce
Amanda T
AT
Liang
Lihua
L
Peti-Peterdi
János
J
Bell
P Darwin
PD
Schwiebert
Erik M
EM
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
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