Apparent species differences in the kinetic properties of P2X₇ receptors

Abstract

1 Apparent species di erences in the responses of recombinant P2X 7 receptors to repeated application of 2'-and 3'-O-(4-benzoylbenzoyl)-ATP (BzATP) have been investigated. 2 Repeated application of 100 mM BzATP resulted in a progressive increase in current magnitude (current growth) at mouse and human, but not rat P2X 7 receptors. 3 Current growth was thought to re¯ect progressive dilation of the P2X 7 ion-channel to a pore permeable to large molecules (MW5900), suggesting that channel dilation was not occurring at the rat P2X 7 receptor. However, 100 mM BzATP produced a rapid in¯ux of YO-PRO-1 (MW375) in cells expressing rat or human P2X 7 receptors. 4 There were, however, species di erences in agonist potency such that 100 mM BzATP was a supra-maximal concentration at rat, but not human or mouse, P2X 7 receptors. Importantly, when sub-maximal concentrations of BzATP or ATP were examined, current growth occurred at rat P2X 7 receptors. 5 The rate of current growth and YO-PRO-1 accumulation increased with agonist concentration and appeared more rapid at rat and human, than at mouse P2X 7 receptors. 6 The potency of BzATP and ATP was 1.5 ± 10 fold lower in naõÈ ve cells than in cells repeatedly exposed to ATP. 7 This study demonstrates that current growth occurs at mouse, rat and human P2X 7 receptors but only when using sub-maximal concentrations of agonist. Previously, current growth was thought to re¯ect the progressive increase in pore diameter of the P2X 7 receptor ion channel, however, the results of this study suggest a progressive increase in agonist potency may also contribute.

Conserved ectodomain cysteines are essential for rat P2X7 receptor trafficking

“…The amplitude of I 1 current generated by 300-μM BzATP application was 1.9±0.4 nA, whereas the mean value of I 1 +I 2 currents at the end of 60-s application was 2.9±0.5 nA (n07). In further accordance with earlier reports [22,51], once the steady level of I 2 current was reached, cells responded to subsequent agonist application with monophasic currents (data not shown).…”

P2X7 receptor activation enhances SK3 channels- and cystein cathepsin-dependent cancer cells invasiveness

“…This property is a particularity of P2X 7 R and is called facilitation (Hibell et al, 2000;Roger et al, 2008Roger et al, , 2010a. This led to a seven times increase of the current density from the first to the eighth ATP application (Figure 2b).…”

“…Extracellular ATP acts as a signalling molecule by activating plasma membrane G protein-coupled P2Y receptors and/or ligand-gated ion channels P2X receptors (Burnstock, 2006). Among the members of the P2X receptors family, the latest cloned P2X 7 receptors (P2X 7 R) (Rassendren et al, 1997) are very unique by different features, some of them are: (1) their sensitivity to ATP (North, 2002), (2) their facilitation under successive or sustained applications of agonist (Hibell et al, 2000;Roger et al, 2008Roger et al, , 2010a and (3) the appearance of a large, non-selective membrane pore after sustained stimulations with ATP (Pelegrin and Surprenant, 2006). Recently, several tumours have been shown to express P2X 7 R at unusually high levels (Adinolfi et al, 2002;Zhang et al, 2004;Slater et al, 2004a, b;Wang et al, 2004a;Raffaghello et al, 2006;Deli et al, 2007;Solini et al, 2008), however, their functionality and involvement in the physiology of cancer cells remain unclear.…”

Mouse Leydig cells express multiple P2X receptor subunits

“…Leydig cells show an EC 50 for ATP around 44 μM [41], which are not consistent with the presence of homomeric P2X 7 receptors. Moreover, the necessity of millimolar concentrations of ATP to stimulate these channels in vivo poses a question about the possible physiological role of these receptors [21]. Another singular property of these receptors is that they have a large pore-forming phenotype specific for P2X7 after long-term stimulation with the agonist, allowing large molecules (>900 Da) to pass [46].…”