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 P2X(7) receptor activation in native tissues. In this study we have further studied the effect of MAPK inhibitors on recombinant and native P2X(7) receptors. EXPERIMENTAL APPROACH: The MAPK inhibitors SB-203580, SB-202190 and SB-242235 were examined in HEK293 cells expressing recombinant P2X(7) receptors and in THP-1 cells expressing native human P2X(7) receptors using a range of experimental approaches. KEY
RESULTS: At human recombinant P2X(7) receptors, SB-203580 and SB-202190 were weak, non-competitive inhibitors (pIC(50)= 4.8 - 6.4) of ethidium accumulation stimulated by 2'- & 3'-O-(4benzoylbenzoyl)-ATP (BzATP) but SB-242235 (0.1-10 microM) had no effect. SB-203580 and SB-202190 had no effect on rat or mouse recombinant P2X(7) receptors and studies with chimeric P2X(7) receptors suggested that SB-203580 was only effective in chimeras containing the N-terminal 255aa of the human P2X(7) receptor. SB-203580 did not consistently affect BzATP-mediated increases in cell calcium levels and, in electrophysiological studies, it slightly decreased responses to 30 microM BzATP but potentiated responses to 100 microM BzATP. In THP1 cells, SB-203580 modestly inhibited BzATP-stimulated ethidium accumulation (pIC(50) 5.7 - < 5) but SB-202190 had no effect. Finally, SB-203580 did not block BzATP-stimulated interleukin-1beta release in THP-1 cells.
CONCLUSIONS: This study confirms that high concentrations of SB-203580 and SB-202190 can block human P2X(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 P2X(7) receptor mediated changes in cellular permeability.