Species and response dependent differences in the effects of MAPK inhibitors on P2X(7) receptor function.

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 – <5) but SB-202190 had no effect. Finally, SB-203580 did not block BzATP-stimulated interleukin-1β release in THP-1 cells.Conclusions:This study confirms that high concentrations of SB-203580 and SB-202190 can block human P2X₇ 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; published online 9 October 2006 [ABSTRACT FROM AUTHOR]