In the present study, we examined whether heterologous expressed human P2X4- and P2X7-receptors form heterooligomers with altered properties. To address this issue, we coexpressed both subunits in Xenopuslaevis oocytes and investigated a possible functional interaction at the level of ATP-induced whole cell currents by means of the two-microelectrode voltage clamp technique. The concentration-response curves as well as the effects of the application of P2X4R- or P2X7R-specifics agonists and blockers showed no evidence for heterotrimeric receptors with a distinct P2X4/P2X7 phenotype. Rather all effects of agonist or blockers could be explained by simultaneous expression of P2X4 and P2X7 homotrimers. However, coexpression with functionally almost inactive P2X7R-mutants or with other channel proteins led to a significant suppression of the P2X4R-dependent currents, which may be explained by a reduction of the expression rate due to the limited expression capacity of the oocytes.