Mechanisms of constitutive and ATP-evoked ATP release in neonatal mouse olfactory epithelium.
BACKGROUND
ATP is an extracellular signaling molecule with many ascribed functions in sensory systems, including the olfactory epithelium. The mechanism(s) by which ATP is released in the olfactory epithelium has not been investigated. Quantitative luciferin-luciferase assays were used to monitor ATP release, and confocal imaging of the fluorescent ATP marker quinacrine was used to monitor ATP release via exocytosis in Swiss Webster mouse neonatal olfactory epithelial slices.


RESULTS
Under control conditions, constitutive release of ATP occurs via exocytosis, hemichannels and ABC transporters and is inhibited by vesicular fusion inhibitor Clostridium difficile toxin A and hemichannel and ABC transporter inhibitor probenecid. Constitutive ATP release is negatively regulated by the ATP breakdown product ADP through activation of P2Y receptors, likely via the cAMP/PKA pathway. In vivo studies indicate that constitutive ATP may play a role in neuronal homeostasis as inhibition of exocytosis inhibited normal proliferation in the OE. ATP-evoked ATP release is also present in mouse neonatal OE, triggered by several ionotropic P2X purinergic receptor agonists (ATP, αβMeATP and Bz-ATP) and a G protein-coupled P2Y receptor agonist (UTP). Calcium imaging of P2X2-transfected HEK293 "biosensor" cells confirmed the presence of evoked ATP release. Following purinergic receptor stimulation, ATP is released via calcium-dependent exocytosis, activated P2X1,7 receptors, activated P2X7 receptors that form a complex with pannexin channels, or ABC transporters. The ATP-evoked ATP release is inhibited by the purinergic receptor inhibitor PPADS, Clostridium difficile toxin A and two inhibitors of pannexin channels: probenecid and carbenoxolone.


CONCLUSIONS
The constitutive release of ATP might be involved in normal cell turn-over or modulation of odorant sensitivity in physiological conditions. Given the growth-promoting effects of ATP, ATP-evoked ATP release following injury could lead to progenitor cell proliferation, differentiation and regeneration. Thus, understanding mechanisms of ATP release is of paramount importance to improve our knowledge about tissue homeostasis and post-injury neuroregeneration. It will lead to development of treatments to restore loss of smell and, when transposed to the central nervous system, improve recovery following central nervous system injury.
Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI 48824, USA.
Sébastien
S
Hayoz
Cuihong
C
Jia
Cc
C
Hegg
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology*; D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D001427:Bacterial Toxins / Q000494:pharmacology; D001973:Bromodeoxyuridine / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology; D002229:Carbenoxolone / Q000494:pharmacology; D002478:Cells, Cultured; D003570:Cytidine Triphosphate / Q000494:pharmacology; D004347:Drug Interactions; D004768:Enterotoxins / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005033:Ethylmaleimide / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects; D005682:Gadolinium / Q000494:pharmacology; D006801:Humans; D051379:Mice; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D009831:Olfactory Mucosa / Q000166:cytology*; D009924:Organ Culture Techniques; D010751:Phosphopyruvate Hydratase / Q000378:metabolism; D058905:Purinergic Agents / Q000494:pharmacology*; D011732:Pyridoxal Phosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D050766:Qb-SNARE Proteins / Q000378:metabolism; D050767:Qc-SNARE Proteins / Q000378:metabolism; D011796:Quinacrine / Q000378:metabolism; D058476:Receptors, Purinergic P2X2 / Q000235:genetics / Q000378:metabolism; D011984:Sensory Receptor Cells / Q000187:drug effects* / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D014544:Uridine Triphosphate / Q000494:pharmacology
D001427:Bacterial Toxins; D004768:Enterotoxins; D004791:Enzyme Inhibitors; D058905:Purinergic Agents; D050766:Qb-SNARE Proteins; D050767:Qc-SNARE Proteins; D058476:Receptors, Purinergic P2X2; C100493:SNAP23 protein, human; C041348:tcdA protein, Clostridium difficile; C077792:pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid; C033901:3'-O-(4-benzoyl)benzoyladenosine 5'-triphosphate; D011732:Pyridoxal Phosphate; D003570:Cytidine Triphosphate; D000255:Adenosine Triphosphate; D005682:Gadolinium; D010751:Phosphopyruvate Hydratase; D001973:Bromodeoxyuridine; D011796:Quinacrine; D002229:Carbenoxolone; D005033:Ethylmaleimide; C038958:gadolinium chloride; D002118:Calcium; D014544:Uridine Triphosphate