Dual Gating Mechanism and Function of P2X7 Receptor Channels

Abstract

The ATP-gated P2X7 receptor channel (P2X7R) operates as a cytolytic and apoptotic receptor but also controls sustained cellular responses, including cell growth and proliferation. However, it has not been clarified how the same receptor mediates such opposing effects. To address this question, we have combined electrophysiological, imaging, and mathematical studies using wild-type and mutant rat P2X7Rs. Activation of naïve (not previously stimulated) receptors by low agonist concentrations caused monophasic slow desensitizing currents and internalization of receptors without other changes in the cellular morphology, much like other P2XRs. In contrast, saturating agonist concentrations induced high-amplitude biphasic currents, reflecting pore dilation and causing rapid cell swelling and lysis. The existence of these two signaling patterns was accounted for using a revised Markov-state model that included, in addition to naïve and sensitized states, desensitized states. Occupancy of one or two ATP-binding sites of naïve receptors favored a slow transition to desensitized states, whereas occupancy of the third binding site favored a transition to sensitized/dilated states. Consistent with model predictions, nondilating P2X7R mutants always generated desensitizing currents. These results suggest that the level of saturation of the ligand binding sites determines the nature of the P2X7R gating and cellular actions.

The P2X7 Receptor Channel: Recent Developments and the Use of P2X7 Antagonists in Models of Disease

“…Once the TM2 domains have moved, the channel pore is fully open and conducts current, the directionality of this being dictated by the membrane potential. After agonist binding and gating rearrangements, monophasic or biphasic currents can be measured by standard wholecell electrophysiology (Yan et al, 2008Khadra et al, 2013). Mono-and biphasic currents through P2X7 channels are distinguished by the agonist concentration and whether the channel is "naive" to agonist or not (Khadra et al, 2013).…”

“…After agonist binding and gating rearrangements, monophasic or biphasic currents can be measured by standard wholecell electrophysiology (Yan et al, 2008Khadra et al, 2013). Mono-and biphasic currents through P2X7 channels are distinguished by the agonist concentration and whether the channel is "naive" to agonist or not (Khadra et al, 2013). However, P2X7 gating is more complex than other ion channels because of the secondary permeability pathway (see section VI).…”

“…Markwardt and colleagues measured a single channel conductance of 9-13 pS for P2X7 in Xenopus laevis oocytes (Riedel et al, 2007a) and have developed extensive kinetic models for the transitions between open and closed states. These kinetic models were recently extended to a 16-state Markov model, taking into account both low-high affinity agonist binding and sensitization/desensitization states (Khadra et al, 2013).…”

HSP90 Regulation of P2X7 Receptor Function Requires an Intact Cytoplasmic C-Terminus

“…In the case of the P2X7R, the time-course of the apparent change in cation permeability is associated with an increase in charge This work was supported by Grant-in-Aid for Scientific Research (C) [No. 26460693] ABBREVIATIONS: 17-AAG, 17-N-allylamino-17-demethoxygeldanamycin; 17-DMAG, 17-dimethylaminoethylamino-17-demethoxygeldanamycin; Bz-ATP, 29 (39)-O-(4-benzoylbenzoyl)adenosine-59-triphosphate; HEK, human embryonic kidney; HSP, heat shock protein; NMDG 1 , N-methyl-transfer across the membrane (called "current facilitation") (Yan et al, 2008(Yan et al, , 2010Khadra et al, 2013;Rokic and Stojilkovic, 2013). In contrast, the long applications of ATP needed to induce the permeability changes in P2X2Rs result in a decrease in charge transfer because the receptor desensitizes (Khakh et al, 1999;Coddou et al, 2015).…”

Escape from adamantane: Scaffold optimization of novel P2X7 antagonists featuring complex polycycles

“…2 However, when this receptor is exposed to high concentrations of ATP for a long period of time, in the high micromolar range, it induces the formation of a nonselective large pore 3 permeable to molecules up to 900 Da, which ultimately triggers cell apoptosis. 4 This ion channel is present in virtually all tissues of the body, being especially abundant in cells of hematopoietic lineage. 5 Due to the widespread presence of the P2X7 receptor in the mammalian organism, its malfunction has been linked to a vast number of pathological conditions, 6 including rheumatoid arthritis (RA), osteoporosis, Parkinson's disease, multiple sclerosis and cancer, among other relevant inflammatory, immune or musculoskeletal disorders.…”