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Inorganic Chemical Pollutants
Published in William J. Rea, Kalpana D. Patel, Reversibility of Chronic Disease and Hypersensitivity, Volume 4, 2017
William J. Rea, Kalpana D. Patel
In addition to acting as a calcium channel blocker, gadolinium, at low concentration, can interact with the signaling involved in intracellular and extracellular ATP hydrolysis.589 Escalada et al.590 reported that 3 μM gadolinium, a concentration that does not block calcium channels, has a potent inhibitory action on ectonucleoside triphosphate diphosphohydrolase (E-NTPDase) activity from the electric organ of Torpedo marmorata. Extracellular nucleotides are important molecules involved in the regulation of different biological processes, including vascular tone. When released as a neurotransmitter from the sympathetic terminals, ATP binds to P2X receptors of vascular smooth muscle cells, producing vasoconstriction. When binding to endothelial P2Y receptors, ATP leads to vasodilatation.589,591 ATP exerts other effects on the vascular beds, such as control of smooth muscle and endothelial cell proliferation.589,591 The action of extracellular nucleotides is terminated by the E-NTPDase family. NTPDase 1 is the major ectonucleotidase expressed in the vasculature589,591 and its action limits platelet activation by ATP hydrolysis.589,591 NTPDase 2 is another ectonucleotidase associated with the vasculature that preferentially converts ATP to ADP.592 Following the action of E-NTPDases, ecto-5′-nucleotidase is responsible for the end of nucleotide signaling by converting AMP to adenosine.593
Intra-carotid body inter-cellular communication
Published in Journal of the Royal Society of New Zealand, 2023
Liam P. Argent, Aabharika Bose, Julian F. R. Paton
Extra-cellular adenosine is either generated via ectonucleotidase degradation of ATP or pumped in to the extra-cellular space through equilibrative nucleoside transporters expressed in the glomus cell plasma membrane (Conde and Monteiro 2004; Conde et al. 2012). Adenosine acts on excitatory A2a receptors localised both to the petrosal afferent post-synaptic membrane and the glomus cell plasma membrane (where A2b receptors are also expressed). Activation of petrosal afferent A2a receptors (which is essential for physiological afferent firing Murali and Nurse 2016) induces depolarisation and thus augments firing (Conde et al. 2006), whilst the binding of adenosine to glomus cell A2a/b receptors raises glomus cell intracellular calcium via the inhibition of background TWIK-related acid sensitive K+ (TASK) channels. This increases membrane excitability (Zhang et al. 2018) and, consequently, also increases the release of neurotransmitters from type I cells (Nurse 2005) that then modulate the effects of adenosine on innervating petrosal afferents. Thus, as with ATP-induced ATP release for amplification, adenosine (which can be ATP-derived) can also provide positive complementary excitation.