P2X₄ receptor re‐sensitization depends on a protonation/deprotonation cycle mediated by receptor internalization and recycling

Abstract

Re-sensitization of P2X receptors depends on a protonation/de-protonation cycle Protonation and de-protonation of the receptors is achieved by internalization and recycling of P2X receptors via acidic compartments Protonation and de-protonation occurs at critical histidine residues within the extracellular loop of P2X receptors Re-sensitization is blocked in the presence of the receptor agonist ATP ABSTRACT: P2X receptors are members of the P2X receptor family of cation-permeable, ligand-gated ion channels that open in response to the binding of extracellular ATP. P2X receptors are implicated in a variety of biological processes, including cardiac function, cell death, pain sensation and immune responses. These physiological functions depend on receptor activation on the cell surface. Receptor activation is followed by receptor desensitization and deactivation upon removal of ATP. Subsequent re-sensitization is required to return the receptor into its resting state. Desensitization and re-sensitization are therefore crucial determinants of P2X receptor signal transduction and responsiveness to ATP. However, the molecular mechanisms controlling desensitization and re-sensitization are not fully understood. In the present study, we provide evidence that internalization and recycling via acidic compartments is essential for P2X receptor re-sensitization. Re-sensitization depends on a protonation/de-protonation cycle of critical histidine residues within the extracellular loop of P2X receptors that is mediated by receptor internalization and recycling. Interestingly, re-sensitization under acidic conditions is completely revoked by receptor agonist ATP. Our data support the physiological importance of the unique subcellular distribution of P2X receptors that is predominantly found within acidic compartments. Based on these findings, we suggest that recycling of P2X receptors regulates the cellular responsiveness in the sustained presence of ATP.

Dissection of P2X4 and P2X7 Receptor Current Components in BV-2 Microglia

“…P2X4 receptors show a long-lasting desensitization behavior, which is partly induced by activation-dependent internalization of these receptors with a slow recycling to the cell membrane [ 31 , 47 , 54 , 57 , 70 , 71 , 72 , 73 ]. If the ATP-activated currents were mediated by P2X4/P2X7 heteromers, one would expect only the current amplitudes to decrease, but the kinetics would not change with repeated ATP applications regardless of the ATP concentration.…”

P2 Purinergic Signaling in the Distal Lung in Health and Disease

“…This triggers a transient Ca 2+ -influx (FACE, fusion activated Ca 2+ -entry) at the site of the LB fusion and provides the Ca 2+ necessary for fusion pore expansion and surfactant release [ 29 , 91 , 92 , 150 ]. FACE is short lasting, and P2X 4 receptors need to be re-sensitized by a protonation/deprotonation cycle depending on receptor internalization and recycling [ 151 ]. It has also been suggested that P2X 4 activation and FACE are part of a positive feedback mechanism, which, due to the increase of Ca 2+ near the apical PM, stimulates additional LB fusions [ 10 ].…”

Contribution of P2X4 Receptors to CNS Function and Pathophysiology

“…As a result, P2X4 is targeted to endosomes, lysosomes and lysosome-related organelles, ensuring a low surface expression not only in neurons, but also in microglia and macrophages [ 54 , 55 ] and there is a dynamic regulation of P2X4 trafficking between the intracellular compartments and the plasma membrane [ 56 ]. In addition to regulating receptor density at the plasma membrane, and thus the response to extracellular ATP, these mechanisms may also accelerate recovery from desensitization [ 57 ], as internalization of P2X4 and trafficking to acidic compartments facilitate re-sensitization of P2X4 [ 58 ]. Indeed, blocking internalization by mutating trafficking motifs within the receptor or using an inhibitor of dynamin increases plasma membrane expression of P2X4R but slows the re-sensitization process of P2X4 [ 56 , 58 ].…”

“…In addition to regulating receptor density at the plasma membrane, and thus the response to extracellular ATP, these mechanisms may also accelerate recovery from desensitization [ 57 ], as internalization of P2X4 and trafficking to acidic compartments facilitate re-sensitization of P2X4 [ 58 ]. Indeed, blocking internalization by mutating trafficking motifs within the receptor or using an inhibitor of dynamin increases plasma membrane expression of P2X4R but slows the re-sensitization process of P2X4 [ 56 , 58 ]. Thus, recycling of P2X4 through the acidic organelles may regulate the cellular responsiveness in the sustained presence of ATP.…”