Roles of P2X receptors and Ca2+ sensitization in extracellular adenosine triphosphate-induced hyperresponsiveness in airway smooth muscle.
BACKGROUND
The release of adenosine triphosphate (ATP) from the airway epithelial cells during the inflammatory process is considered to play an important role in the pathophysiology of asthma and chronic obstructive pulmonary disease.


OBJECTIVE
This study was designed to determine whether extracellular ATP is involved in the bronchial hyperresponsiveness as an interaction between epithelium and smooth muscle in the airways.


METHODS
We examined the contractile response to methacholine (MCh) before and after exposure to low concentrations (< or = 10 microm) of ATP in isolated, epithelium-denuded guinea-pig tracheal smooth muscle by measuring isometric tension. Intracellular Ca2+ concentrations ([Ca2+]i) were assessed by fluorescent intensities of fura-2.


RESULTS
MCh-induced contractile force was increased with no change in [Ca2+]i after exposure to 10 microm ATP for 15 min. The ability of ATP to enhance the MCh-induced contraction was markedly attenuated by suramin, a non-selective P2 receptor inhibitor. Pre-incubation with ATPgammaS, a non-hydrolysable analogue of ATP and alpha,beta-meATP, a P2X agonist, also enhanced the MCh-induced contraction. In contrast, uracil triphosphate, a P2Y agonist, did not affect the MCh-induced contraction. Y-27632, a Rho-kinase inhibitor, suppressed the ability of ATP to enhance the MCh-induced contraction. Moreover, PP1 and PP2, Src tyrosin kinase inhibitors, suppressed the enhancement of MCh-induced contraction by ATP.


CONCLUSIONS
Pre-treatment with ATP induces hyperresponsiveness to MCh mediated by Ca2+ sensitization via the P2X receptor in airway smooth muscle. The present findings suggest the possible involvement of both the Rho-kinase and Src pathways in the intracellular mechanism of this phenomenon.
Oguma
T
T
Department of Respiratory Medicine, Nagoya University Graduate School of Medicine, Nagoya, Japan.
Ito
S
S
Kondo
M
M
Makino
Y
Y
Shimokata
K
K
Honjo
H
H
Kamiya
K
K
Kume
H
H
D000255:Adenosine Triphosphate / Q000819:agonists / Q000031:analogs & derivatives / Q000276:immunology / Q000378:metabolism / Q000494:pharmacology*; D000577:Amides / Q000494:pharmacology; D000818:Animals; D001980:Bronchi / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D016535:Bronchial Hyperreactivity / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D016085:Bronchoconstrictor Agents / Q000819:agonists / Q000494:pharmacology; D002118:Calcium / Q000276:immunology / Q000378:metabolism; D020013:Calcium Signaling / Q000276:immunology; D002478:Cells, Cultured; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006168:Guinea Pigs; D047908:Intracellular Signaling Peptides and Proteins / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism; D007537:Isometric Contraction / Q000187:drug effects / Q000276:immunology; D008297:Male; D016210:Methacholine Chloride / Q000819:agonists / Q000494:pharmacology; D032389:Myocytes, Smooth Muscle / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D009924:Organ Culture Techniques; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism; D029424:Pulmonary Disease, Chronic Obstructive / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D058910:Purinergic P2 Receptor Agonists; D011725:Pyridines / Q000494:pharmacology; D018048:Receptors, Purinergic P2 / Q000276:immunology / Q000378:metabolism; D058469:Receptors, Purinergic P2X; D020545:Respiratory Mucosa / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D013997:Time Factors; D054460:rho-Associated Kinases; D019061:src-Family Kinases / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism
D000577:Amides; D016085:Bronchoconstrictor Agents; D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; D058910:Purinergic P2 Receptor Agonists; D011725:Pyridines; D018048:Receptors, Purinergic P2; D058469:Receptors, Purinergic P2X; D016210:Methacholine Chloride; C108830:Y 27632; D000255:Adenosine Triphosphate; D019061:src-Family Kinases; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; D010749:Phosphoprotein Phosphatases; D002118:Calcium