A remarkable feature of a sustained P2X7 receptor activation by ATP is the induction of a large cytolytic pore permeable to large organic cations. Whether the cytolytic pore is formed by the homotrimeric P2X7 receptor itself or by the downstream activation of secondary channel proteins such as pannexin-1 (PanX1) is still debated. Here, we investigated the specificity of functional and physical interaction between pannexin-1 and the P2X7 receptor. Recombinant PanX1 and the P2X7 receptor expressed in Xenopus laevis oocytes form disulfide-bonded oligomers in the endoplasmic reticulum (ER). However, at the level of the plasma membrane, we could not detect disulfide-bonded oligomers between PanX1 and hP2X7 nor any non-covalently linked physically stable complexes between the two proteins. This suggests that the disulfide-bonded oligomers are retained in the ER by the ER quality control system. Moreover, by using two-electrode voltage-clamp electrophysiology, although typical pannexin-dependent currents could be measured at positive membrane potentials, we obtained no evidence for a functional interaction of human or murine P2X7 receptors and PanX1 before and during P2X7 receptor activation by ATP. Although our data confirm that certain forms of P2X7 receptors and PanX1 interact physically stably with each other, they argue against the view that this interaction takes place at the cell membrane and that PanX1 represents the pore-forming principle activated through P2X7 receptors.

We thank the German Research foundation (Deutsche Forschungsgemeinschaft, DFG) for financial support (grants Ma1581/15-1 and Schm536/9-1)