Activation of specific ATP receptors induces a rapid increase in intracellular calcium ions in rat hypothalamic neurons.
We have used real-time dynamic video imaging of Fura-2 fluorescence to study the acute effects of external ATP on [Ca2+]i in cultured rat hypothalamic neurons. The addition of ATP at microM concentrations, but not adenosine, AMP, ADP or GTP, produced a rapid, dose-dependent increase in cytosolic Ca2+. The hydrolysis-resistant ATP analogues 3-thio-ATP and beta,gamma-imido-ATP produced a similar response but alpha,beta-methylene ATP had much lower efficacy. The ATP response was inhibited by 10 microM nifedipine, abolished by 50 microM cadmium and by the absence of extracellular Ca2+, but was unaffected by ryanodine or omega-conotoxin GVIA. The P2-purinoceptor antagonist suramin reversibly and selectively inhibited the ATP response but had no effect on other neurotransmitter-induced Cai2+ responses. Antagonists to muscarinic, nicotinic, NMDA, non-NMDA, GABA, 5-HT and adenosine receptors had no effect on the ATP response. Thus the Ca2+ response of hypothalamic neurons to ATP is mediated by specific suramin-sensitive ATP-receptors, activation of which is independent of ATP hydrolysis and results in an influx of extracellular Ca2+ largely through high voltage-gated Ca2+ channels. These findings support the assertion that ATP acts in the CNS as an excitatory neurotransmitter.
Department of Medicine, University of Bristol, UK.
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Chen
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Levy
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Lightman
D000241:Adenosine / Q000494:pharmacology; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000249:Adenosine Monophosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D005333:Fetus; D006160:Guanosine Triphosphate / Q000494:pharmacology; D007031:Hypothalamus / Q000378:metabolism*; D007700:Kinetics; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017981:Receptors, Neurotransmitter / Q000037:antagonists & inhibitors; D018048:Receptors, Purinergic P2 / Q000187:drug effects / Q000502:physiology*; D013329:Structure-Activity Relationship; D013498:Suramin / Q000494:pharmacology
D017981:Receptors, Neurotransmitter; D018048:Receptors, Purinergic P2; D000249:Adenosine Monophosphate; D013498:Suramin; D000244:Adenosine Diphosphate; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D000241:Adenosine; D002118:Calcium