Molecular Probes for P2X7 Receptor Studies

Abstract

The ionotropic P2X7 receptor (P2X7R) has become the focus of intense research interest for a number of reasons: i) it is a cation selective ion channel that is modulated by extracellular ATP. Upon stimulation by high concentrations of ATP it generates a non-selective membrane pore which is permeable to hydrophilic molecules with molecular weight up to 900 Da. ii) Though its physiological function is yet to be fully understood, there is high P2X7R expression in microglia. Importantly, this implies a pivotal role for the P2X7R in neuro-inflammatory and -degenerative processes. In addition, P2X7R-stimulated release of traditional neurotransmitters in the brain, such as glutamate and GABA, further supports the involvement of P2X7R in neuro-inflammatory and -degenerative processes. P2X7-knockout animals are also found to be resistant to inflammation and neuropathic pain, which suggests that P2X7 antagonists could potentially serve as all-purpose analgesics. Recent advances in the development of P2X7R ligands have resulted in identification of several different classes of P2X7R antagonists, including ATP analogues (oxidized ATP), dyes (Brilliant Blue G), tyrosine derivatives (KN-62 and KN-04), cyclic imides, adamantane and benzamide derivatives. A KN-62 related radioligand has also recently been reported for use in receptor binding assays. A more extensive range of potent, selective P2X7R ligands is required for a better understanding of the cascade of cellular processes associated with the P2X7R. This article will review P2X7R ligands discovered to date, together with their biological activity and therapeutic potential.

Identification and characterization of a novel variant of the human P2X7 receptor resulting in gain of function

“…The purinergic P2X 7 receptor, previously known as P2Z, is the seventh member of the P2X receptor family of ligandgated ion channels activated by extracellular adenosine triphosphate (ATP) [1]. All of the P2X receptors contain two membrane-spanning domains, intracellular amino and carboxy termini, and an extracellular domain of approximately 280 amino acids containing the ligand-binding site and ten conserved cysteine residues that likely form intrachain disulfide bonds to give secondary structure to the receptor [2][3][4][5].…”

“…All of the P2X receptors contain two membrane-spanning domains, intracellular amino and carboxy termini, and an extracellular domain of approximately 280 amino acids containing the ligand-binding site and ten conserved cysteine residues that likely form intrachain disulfide bonds to give secondary structure to the receptor [2][3][4][5]. P2X 7 receptors differ from other P2X receptor subtypes (P2X [1][2][3][4][5][6] ) by an extended cytoplasmic carboxy-terminal tail (240 aa) which may be responsible for the unique ability of P2X 7 to form large pores in the membrane after prolonged agonist stimulation [1]. The P2X 7 receptor exhibits several unusual properties.…”

“…P2X 7 receptors differ from other P2X receptor subtypes (P2X [1][2][3][4][5][6] ) by an extended cytoplasmic carboxy-terminal tail (240 aa) which may be responsible for the unique ability of P2X 7 to form large pores in the membrane after prolonged agonist stimulation [1]. The P2X 7 receptor exhibits several unusual properties. Following brief activation by agonist, P2X 7 forms a channel with strong selectivity for the divalent cations Ca 2+ and Ba 2+ over monovalent cations [6].…”

“…Following brief activation by agonist, P2X 7 forms a channel with strong selectivity for the divalent cations Ca 2+ and Ba 2+ over monovalent cations [6]. Continued stimulation by agonist results in the formation of a non-selective pore that allows permeation of inorganic and organic cationic molecules up to 900 Da, such as ethidium bromide, propidium iodide (PI), and quinolinium fluorescent dyes YO-PRO-1 [4,7]. Recent studies suggest that the large pore may reflect coupling to a pannexin hemichannel [8].…”

“…P2X 7 receptors are predominantly expressed on cells from the hematopoietic lineages, such as erythrocytes, lymphocytes, neutrophils, eosinophils, mast cells, monocytes, and macrophages [9][10][11][12][13][14][15][16][17][18]. It has been reported recently that P2X 7 receptors are expressed in central and spinal cord neurons [19][20][21][22].…”