The rat ATP P2X₄ receptor was expressed in Xenopus laevis oocytes to assess the effect of zinc and copper as possible regulators of purinergic mechanisms. ATP applied for 20 s evoked an inward cationic current with a median effective concentration (EC₅₀) of 21.4 ± 2.8 μM and a Hill coefficient (n_H) of 1.5 ± 0.1. Coapplication of ATP plus 10 μM zinc displaced leftward, in a parallel fashion, the ATP concentration‐response curve, reducing the EC₅₀ to 8.4 ± 1.8 μM (p < 0.01) without altering the receptor n_H. The zinc potentiation was fast in onset, easily reversible, and voltage‐independent and did not require metal preexposure. The zinc EC₅₀ was 2‐5 μM, with a bell‐shaped curve. At concentrations of 100‐300 μM, zinc produced less potentiation, and at 1 mM, it inhibited 50% the ATP current. The effect of zinc was mimicked by cadmium. In contrast, copper inhibited the ATP‐evoked currents in a time‐ and concentration‐dependent fashion, reducing the maximal current (I_max) without altering the EC₅₀. The copper‐induced inhibition was slow in onset, slowly reversible, and voltage‐independent. Whereas coapplication of 300 μM copper plus ATP reduced I_max to 36.2 ± 5%, the coapplication of, or 60‐s preexposure by, 10 μM copper reduced I_max to 79 ± 9.2% (p < 0.05) and 39.6 ± 8.7% (p < 0.01), respectively. The inhibition was noncompetitive in nature and mimicked by mercury. Cobalt, barium, and manganese did not modify significantly the ATP‐evoked current, demonstrating metal specificity. The simultaneous 1‐min preapplication of both metals revealed that the 10 μM zinc‐induced potentiation was obliterated by 10 μM copper, whereas 30 μM copper not only reduced the potentiation, but inhibited the ATP response. Following coapplication of both metals for 20 s with ATP, at least 100 μM copper was required to counteract the 10 μM zinc‐induced potentiation. The simultaneous preincubation with both metals provided evidence for a noncompetitive interaction. We hypothesize the existence of metal binding site(s), which are most likely localized in the extracellular domain of the P2X₄ receptor structure. These sites are selective and accessible to extracellular metal applications and bind micromolar concentrations of metals. The present results are compatible with the working hypothesis that trace metals, such as copper and zinc, are physiological modulators of the P2X₄ receptor. The modulation of brain purinergic transmission by physiologically and toxicologically relevant trace metal cations is highlighted.

The P2X₇ receptor is a non‐selective cationic channel activated by extracellular ATP, belonging to the P2X receptor family. To assess the role of extracellular histidines on the allosteric modulation of the rat P2X₇ receptor by divalent metals (copper, zinc and magnesium) and protons, these amino acid residues were singly substituted for corresponding alanines. Wild‐type and mutated receptors were injected to Xenopus laevis oocytes; metal‐related effects were evaluated by the two‐electrode voltage‐clamp technique. Copper inhibited the ATP‐gated currents with a median inhibitory concentration of 4.4 ± 1.0 µmol/L. The inhibition was non‐competitive and time‐dependent; copper was 60‐fold more potent than zinc. The mutant H267A, resulted in a copper resistant receptor; mutants H201A and H130A were less sensitive to copper inhibition (p < 0.05). The rest of the mutants examined, H62A, H85A, and H219A, conserved the copper‐induced inhibition. Only mutants H267A and H219A were less sensitive to the modulator action of zinc. Moreover, the magnesium‐induced inhibition was abolished exclusively on the H130A and H201A mutants, suggesting that this metal may act at a novel cationic modulator site. Media acidification inhibited the ATP‐gated current 87 ± 3%; out of the six mutants examined, only H130A was significantly less sensitive to the change in pH, suggesting that His‐130 could be involved as a pH sensor. In conclusion, while His‐267 is critically involved in the copper or zinc allosteric modulation, the magnesium inhibitory effects is related to His‐130 and His‐201, His‐130 is involved in proton sensing, highlighting the role of defined extracellular histidines in rat P2X₇ receptor allosteric modulation.

The P2X7 receptor is a ligand-gated, cation-selective channel whose main physiological ligand is ATP. P2X7 receptor activation may also be triggered by ARTC2.2-dependent ADP ribosylation in the presence of extracellular NAD. Upon activation, this receptor induces several responses, including the influx of calcium and sodium ions, phosphatidylserine externalization, the formation of a non-selective membrane pore, and ultimately cell death. P2X7 receptor activation depends on the availability of extracellular nucleotides, whose concentrations are regulated by the action of extracellular nucleotidases such as CD39 and CD38. The P2X7 receptor has been extensively studied in the context of the immune response, and it has been reported to be involved in inflammasome activation, cytokine production, and the migration of different innate immune cells in response to ATP. In adaptive immune responses, the P2X7 receptor has been linked to T cell activation, differentiation, and apoptosis induction. In this review, we will discuss the evidence of the role of the P2X7 receptor on T cell differentiation and in the control of T cell responses in inflammatory conditions.

Sepsis progresses to multiple organ dysfunction due to the uncontrolled release of inflammatory mediators, and a growing body of evidence shows that neural signals play a significant role in modulating the immune response. Thus, similar toall other physiological systems, the immune system is both connected to and regulated by the central nervous system. The efferent arc consists of the activation of the hypothalamic–pituitary–adrenal axis, sympathetic activation, the cholinergic anti-inflammatory reflex, and the local release of physiological neuromodulators. Immunosensory activity is centered on the production of pro-inflammatory cytokines, signals that are conveyed to the brain through different pathways. The activation of peripheral sensory nerves, i.e., vagal paraganglia by the vagus nerve, and carotid body (CB) chemoreceptors by the carotid/sinus nerve are broadly discussed here. Despite cytokine receptor expression in vagal afferent fibers, pro-inflammatory cytokines have no significant effect on vagus nerve activity. Thus, the CB may be the source of immunosensory inputs and incoming neural signals and, in fact, sense inflammatory mediators, playing a protective role during sepsis. Considering that CB stimulation increases sympathetic activity and adrenal glucocorticoids release, the electrical stimulation of arterial chemoreceptors may be suitable therapeutic approach for regulating systemic inflammation.