Chelerythrine and other benzophenanthridine alkaloids block the human P2X 7 receptor

Extracellular ATP can activate a cation‐selective channel/pore on human B‐lymphocytes, known as the P2X 7 receptor. Activation of this receptor is linked to PLD stimulation. We have used ATP‐induced 86 Rb + (K + ) efflux to examine the effect of benzophenanthridine alkaloids on P2X 7 channel/pore function in human B‐lymphocytes. Both ATP and the nucleotide analogue 2′‐3′‐ O ‐(4‐benzoylbenzoyl)‐ATP (BzATP) induced an 86 Rb + efflux, which was completely inhibited by the isoquinoline derivative 1‐( N , O ‐bis[5‐isoquinolinesulphonyl]‐ N ‐methyl‐ L ‐tyrosyl)‐4‐phenylpiperazine (KN‐62), a potent P2X 7 receptor antagonist. The benzophenanthridine alkaloid chelerythrine, a potent PKC inhibitor, inhibited the ATP‐induced 86 Rb + efflux by 73.4±3.5% and with an IC 50 of 5.6±2.3 μ M . Similarly, other members of this family of compounds, sanguinarine and berberine, blocked the ATP‐induced 86 Rb + efflux by 58.8±4.8 and 61.1±8.0%, respectively. Concentration–effect curves to ATP estimated an EC 50 value of 78 μ M and in the presence of 5 and 10 μ M chelerythrine this increased slightly to 110 and 150 μ M , respectively, which fits a noncompetitive inhibitor profile for chelerythrine. Chelerythrine at 10 μ M was effective at inhibiting the ATP‐induced PLD stimulation in B‐lymphocytes by 94.2±21.9% and the phorbol 12‐myristate 13‐acetate‐induced PLD stimulation by 68.2±7.4%. This study demonstrates that chelerythrine in addition to PKC inhibition has a noncompetitive inhibitory action on the P2X 7 receptor itself.British Journal of Pharmacology (2004) 142 , 1015–1019. doi: 10.1038/sj.bjp.0705868