Subtype-Specific Mechanisms for Functional Interaction between a6b4* Nicotinic Acetylcholine Receptors and P2X Receptors

P2X receptors and nicotinic acetylcholine receptors (nAChRs) display functional and physical interactions in many cell types and heterologous expression systems, but interactions between a6b4-containing (a6b4*) nAChRs and P2X2 receptors and/or P2X3 receptors have not been fully characterized. We measured several types of crosstalk in oocytes coexpressing a6b4 nAChRs and P2X2, P2X3, or P2X2/3 receptors. A novel form of crosstalk occurs between a6b4 nAChRs and P2X2 receptors. P2X2 receptors were forced into a prolonged desensitized state upon activation by ATP through a mechanism that does not depend on the intracellular C terminus of the P2X2 receptors. Coexpression of a6b4 nAChRs with P2X3 receptors shifts the ATP dose-response relation to the right, even in the absence of acetylcholine (ACh). Moreover, currents become nonadditive when ACh and ATP are coapplied, as previously reported for other Cys-loop receptors interacting with P2X receptors, and this crosstalk is dependent on the presence of the P2X3 C-terminal domain. P2X2 receptors also functionally interact with a6b4b3 but through a different mechanism from a6b4. The interaction with P2X3 receptors is less pronounced for the a6b4b3 nAChR than the a6b4 nAChR. We also measured a functional interaction between the a6b4 nAChRs and the heteromeric P2X2/3 receptor. Experiments with the nAChR channel blocker mecamylamine on P2X2–a6b4 oocytes point to the loss of P2X2 channel activity during the crosstalk, whereas the ion channel pores of the P2X receptors were fully functional and unaltered by the receptor interaction for P2X2–a6b4b3, P2X2/3–a6b4, and P2X2/3–a6b4b3. These results may be relevant to dorsal root ganglion cells and to other neurons that coexpress these receptor subunits.