IDENTIFICATION OF P2X7 (P2Z) RECEPTOR IN N18TG-2 CELLS AND NG108-15 CELLS

ATP activates a nonselective cation current by stimulating the P2Z rec eptor in NG108-15 cells-a hybrid cell line of the mouse neuroblastoma N18TG-2 cells and the rat glioma C6Bu-1 cells. Recently, the P2X7 rece ptor was cloned from the rat brain and was found to have electrophysio logical properties similar to those of the P2Z receptor. We examined t he expression of P2X7 receptor mRNA in NG108-15 cells as well as in th eir parent cell lines, N18TG-2 and C6Bu-1 cells, by reverse transcript ion-polymerase chain reaction (RT-PCR). The cDNA templates from these cell lines were amplified with primers specific to the P2X7 receptor s equence. Positive signals were detected in the RT-PCR products from NG 108-15 and N18TG-2 cells but not from C6Bu-1 cells. We next examined t he effect of ATP on the membrane current in N18TG-2 cells and C6Bu-1 c ells by whole-cell voltage clamp. In N18TG-2 cells, ATP induced a sust ained current with a reversal potential of 9.3 +/- 1.2 mV (n = 22) in a concentration-dependent manner with an EC50 of 1.76 +/- 0.18 mM (n = 36). In contrast, ATP (1 mM) did not induce any current in C6Bu-1 cel ls. The ATP-induced current in N18TG-2 cells resembled that in NG108-1 5 cells in the following points: (a) The currents did not desensitize significantly. (b) EC50 values of ATP are of millimolar order. (c) Ben zoylbenzoyl-ATP was a more potent agonist than ATP. (d) The current wa s larger in methanesulfonate than in Cl- external solution. (a) The cu rrent was larger at lower external Mg2+ concentrations. These results suggest that the hybrid NG108-15 cells possess a P2X7 receptor like th e P2Z receptor and that the ability of expressing this channel origina tes from N18TG-2 cells but not from C6Bu-1 cells.