The P2X7 receptor is a member of the P2X receptor family containing ion channels, which are opened by binding of extracellular ATP and are permeable to small cations with a diameter of < 9 Å. A marked feature of sustained P2X7 receptor activation by high ATP concentrations is the induction of a large cytolytic pore permeable to cations up to 900 Da. Because the view has been strengthened that the cytolytic pore is not formed by the P2X7 receptor itself, pannexin-1 is considered as an attractive candidate as P2X7 receptor-associated pore-forming channel protein. Here, we investigated whether a functional interaction exists between pannexin-1 and P2X7 receptors. P2X7 receptors and pannexin-1 were co-expressed in Xenopus laevis oocytes. Cell membrane currents were measured by the two microelectrode voltage clamp technique. Verification of functional pannexin-1 expression was performed by measuring ion currents induced by a voltage ramp going from -100 to +100 mV within 60 s. For investigating P2X7 receptor-dependent ion conductances, 0.1 mM free ATP^4- was applied for about 1 min and the ATP-induced conductance was measured by periodically depolarizing the membrane potential from -60 to +40 mV within 1 s in a ramp-like fashion. The coexpression of pannexin-1 with P2X7 receptors did not change the ATP-induced conductance. The results obtained for the functional interaction measurements between human P2X7-human pannexin-1 and mouse P2X7-mouse pannexin-1 were similar. We therefore conclude that pannexin-1 is not involved in the P2X7 receptor-mediated induction of pores for large cations.