Agonist potency at P2X7 receptors is modulated by structurally diverse lipids

Background and purpose: The P2X(7) receptor exhibits a high degree of plasticity with agonist potency increasing after prolonged receptor activation. In this study we investigated the ability of lipids to modulate agonist potency at P2X7 receptors. Experimental approach: A variety of lipids, including lysophosphatidylcholine, sphingosylphosphorylcholine and hexadecylphosphorylcholine were studied for their effect on P2X(7) receptor-stimulated ethidium bromide accumulation in cells expressing human recombinant P2X(7) receptors and on P2X(7) receptor-stimulated interleukin-1 beta (IL1 beta) release from THP-1 cells. The effects of the lipids were also assessed in radioligand binding studies on human P2X(7) receptors. Key results: At concentrations (3-30 mu M) below the threshold to cause cell lysis, the lipids increased agonist potency and/or maximal effects at P2X(7) receptors in both ethidium accumulation and IL1b release studies. There was little structure activity relationship ( SAR) for this effect and sub- lytic concentrations of Triton X- 100 partially mimicked the effects of the lipids. The lipids caused cell lysis and increased intracellular calcium at higher concentrations ( 30- 100 mu M) which complicated interpretation of their effects in functional studies. However, the lipids ( 3- 100 mu M) also increased agonist potency 30- 100 fold in radioligand binding studies. Conclusions and implications: This study demonstrates that a diverse range of lipids increase agonist potency at the P2X(7) receptor in functional and binding studies. The broad SAR, including the effect of Triton X- 100, suggests this may reflect changes in membrane properties rather than a direct effect on the P2X(7) receptor. Since many of the lipids studied accumulate in disease states they may enhance P2X(7) receptor function under pathophysiological conditions.