Co-release of ATP and ACh mediates hypoxic signalling at rat carotid body chemoreceptors.

Abstract

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.

• Authors: M Zhang, H Zhong, C Vollmer, C A Nurse
• Journal: The Journal of physiology (J Physiol) Vol. 525 Pt 1 Pg. 143-58 (May 15 2000) ISSN: 0022-3751 [Print] England
• PMID: 10811733 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Cholinergic Antagonists
• Purinergic P2 Receptor Antagonists
• Hexamethonium
• Suramin
• Adenosine Triphosphate
• Tyrosine 3-Monooxygenase
• Acetylcholine
• Oxygen

Topics

• Acetylcholine (metabolism)
• Adenosine Triphosphate (analogs & derivatives, metabolism)
• Animals
• Carotid Body (drug effects, metabolism)
• Cell Hypoxia
• Cells, Cultured
• Chemoreceptor Cells (metabolism)
• Cholinergic Antagonists (pharmacology)
• Coculture Techniques
• Fluorescent Antibody Technique
• Hexamethonium (pharmacology)
• Membrane Potentials (drug effects)
• Neurons (drug effects, metabolism)
• Oxygen (metabolism)
• Patch-Clamp Techniques
• Purinergic P2 Receptor Antagonists
• Rats
• Suramin (pharmacology)
• Tyrosine 3-Monooxygenase (metabolism)