ISOQUINOLINES AS ANTAGONISTS OF THE P2X(7) NUCLEOTIDE RECEPTOR - HIGHSELECTIVITY FOR THE HUMAN VERSUS RAT RECEPTOR HOMOLOGS

nesulfonyl)-N-methyl-L-tyrosyl]-4-phenylpiperazine (KN-62) and N-[1-[N -methyl-p-(5 isoquinolinesulfonyl)benzyl]-2-(4 phenylpiperazine)ethyl] -5-isoquino-linesulfonamide (KN-04) potently inhibit the human lymphoc yte P2Z receptor, an ATP-gated cation channel [Br J Pharmacol 120:1483 -1490 (1997)]. Although the molecular identity of the lymphocyte P2Z r eceptor has not been established, it shares many functional characteri stics with the cloned P2X(7) nucleotide receptor. We have tested wheth er these isoquinolines inhibit P2X receptor function in human embryoni c kidney 293 cells that stably express the human or rat recombinant P2 X(7) receptors. ATP activation of cation currents and uptake of the or ganic dye ethidium were potently inhibited by KN-62 and KN-04 in human embryonic kidney cells expressing the human P2X(7)R but not the rat P 2X(7)R, even though these species homologues share 80% amino acid iden tity. Introduction of the first 335 amino acids of the human P2X(7)R s equence conferred KN-62 sensitivity to the rat P2X(7)R; this suggests that isoquinolines interact with residues in the amino-terminal half ( containing the large extracellular loop) of the human P2X(7)R. KN-62 a nd KN-04 also potently inhibited ATP-gated Ca2+ influx and ethidium up take in several leukocyte cell lines (THP-1, BAC1.2f5, and BW5147) tha t natively express the human or murine P2X(7)R mRNA, The ability of is oquinoline sulfonamides to potently inhibit human and murine P2X(7)R s ignaling will be a useful tool for identifying P2Z/P2X(7) functional r esponses in other cell types. The substantial differences in pharmacol ogical sensitivity between rat and human P2X(7)R may also indicate str uctural domains important in channel/pore activation.