Purinergic P2X(1) and P2X(7) receptors are co-expressed in several cell types such as lymphocytes or epithelial cells. Here we examined whether these two P2X subtypes interact with each other in a manner that results in a mutual alteration of their electrophysiologic behaviour. Furthermore, since specific pharmacological tools are needed to assign distinct effects to a particular receptor subtype in native cells, we assessed a series of compounds for their capacity to separate individual current components in cells that co-expressed both receptor subtypes. In Xenopus oocytes, co-expression neither changed the time courses of activation, desensitization and deactivation nor recovery from desensitization when compared to oocytes that express either hP2X(1) or hP2X(7) receptors alone. A selective activation of hP2X(7) receptors was achieved with benzoyl-benzoyl-ATP, which did not activate P2X(1) receptor currents. P2X(7) receptors could also be selectively activated by ATP when co-applied with 1 microM NF449, a suramin derivative, which is 100,000 fold more potent in blocking P2X(1) than P2X(7) receptors. alphabeta-methylene-ATP, a reportedly hP2X(1) receptor-specific agonist, as well as oxidized-ATP, brilliant blue or KN62, reported hP2X(7) receptor antagonists, were found to be ineffective in separating hP2X(1) receptor current from the P2X(7) current. The best way for a selective activation of the hP2X(1) receptor component in cells co-expressing the P2X(7) receptor is the application of low concentrations of ATP (< 1 microM) or the addition of Mg2+ when using higher concentrations of ATP.