Species and response dependent differences in the effects of MAPK inhibitors on P2X7 receptor function

Abstract

Background: Recent studies have implicated the mitogen activated protein kinase (MAPK) in cellular permeability changes following P2X₇ receptor activation in native tissues. In this study we have further studied the effect of MAPK inhibitors on recombinant and native P2X₇ receptors. Experimental Approach: The MAPK inhibitors SB‐203580, SB‐202190 and SB‐242235 were examined in HEK293 cells expressing recombinant P2X₇ receptors and in THP‐1 cells expressing native human P2X₇ receptors using a range of experimental approaches. Key results: At human recombinant P2X₇ receptors, SB‐203580 and SB‐202190 were weak, non‐competitive inhibitors (pIC₅₀= 4.8 ‐ 6.4) of ethidium accumulation stimulated by 2’‐ & 3’‐O‐(4benzoylbenzoyl)‐ATP (BzATP) but SB‐242235 (0.1‐10μM) had no effect. SB‐203580 and SB‐202190 had no effect on rat or mouse recombinant P2X₇ receptors and studies with chimeric P2X₇ receptors suggested that SB‐203580 was only effective in chimeras containing the N‐terminal 255aa of the human P2X₇ receptor. SB‐203580 did not consistently affect BzATP‐mediated increases in cell calcium levels and, in electrophysiological studies, it slightly decreased responses to 30μM BzATP but potentiated responses to 100μM BzATP. In THP1 cells, SB‐203580 modestly inhibited BzATP‐stimulated ethidium accumulation (pIC₅₀ 5.7 – 7 receptor‐mediated increases in cellular ethidium accumulation but suggest this is not related to MAPK inhibition. Overall, the data cast doubt on a general role of MAPK in mediating P2X₇ receptor mediated changes in cellular permeability. British Journal of Pharmacology (2006) 149, 948–957. doi:10.1038/sj.bjp.0706938