Co-release of ATP and ACh mediates hypoxic signalling at rat carotid body chemoreceptors.
Using functional co-cultures of rat carotid body (CB) O2 chemoreceptors and 'juxtaposed' petrosal neurones (JPNs), we tested whether ATP and ACh acted as co-transmitters. Perforated-patch recordings from JPNs often revealed spontaneous and hypoxia-evoked (PO2 approximately 5 mmHg) excitatory postsynaptic responses. The P2X purinoceptor blocker, suramin (50 microM) or a nicotinic ACh receptor (nAChR) blocker (hexamethonium, 100 microM; mecamylamine, 1 microM) only partially inhibited these responses, but together, blocked almost all activity. Under voltage clamp (-60 mV), fast perfusion of 100 microM ATP over hypoxia-responsive JPNs induced suramin-sensitive (IC50 = 73 microM), slowly-desensitizing, inward currents (IATP) with time constant of activation tauon = 30.6 +/- 4. 8 ms (n = 7). IATP reversed at 0.33 +/- 3.7 mV (n = 4), and the dose-response curve was fitted by the Hill equation (EC50 = 2.7 microM; Hill coefficient approximately 0.9). These purinoceptors contained immunoreactive P2X2 subunits, but their activation by alpha,beta-methylene ATP (alpha,beta-meATP; EC50 = 2.1 microM) suggests they are P2X2/P2X3 heteromultimers. Suramin and nAChR blockers inhibited the extracellular chemosensory discharge in the intact rat carotid body-sinus nerve preparation in vitro. Further, P2X2 immunoreactivity was widespread in rat petrosal ganglia in situ, and co-localized in neurones expressing the CB chemo-afferent marker, tyrosine hydroxylase (TH). P2X2 labelling in the CB co-localized with nerve-terminal markers, and was intimately associated with TH-positive type 1 cells. Thus ATP and ACh are co-transmitters during chemotransduction in the rat carotid body.
Zhang
M
M
Department of Biology, McMaster University, Hamilton, Ontario, Canada L8S 4K1.
Zhong
H
H
Vollmer
C
C
Nurse
C A
CA
D000109:Acetylcholine / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism*; D000818:Animals; D002344:Carotid Body / Q000187:drug effects / Q000378:metabolism*; D015687:Cell Hypoxia; D002478:Cells, Cultured; D002628:Chemoreceptor Cells / Q000378:metabolism*; D018680:Cholinergic Antagonists / Q000494:pharmacology; D018920:Coculture Techniques; D005455:Fluorescent Antibody Technique; D018738:Hexamethonium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D058919:Purinergic P2 Receptor Antagonists; D051381:Rats; D013498:Suramin / Q000494:pharmacology; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism
D018680:Cholinergic Antagonists; D058919:Purinergic P2 Receptor Antagonists; D018738:Hexamethonium; D013498:Suramin; D000255:Adenosine Triphosphate; D014446:Tyrosine 3-Monooxygenase; D000109:Acetylcholine; D010100:Oxygen