Gap junction channels coordinate the propagation of intercellular Ca ²⁺ signals generated by P2Y receptor activation

Astrocytes express gap junction proteins and multiple types of P2Y receptors (P2YRs) that contribute to the propagation of intercellular Ca ²⁺ waves (ICW). To gain access to the role played by gap junctional communication in ICW propagation generated by P2YR activation, we selectively expressed P2Y_1,2,4R subtypes and Cx43 in the human 1321N1 astrocytoma cell line, which lacks endogenous P2 receptors. Fluorescence recovery after photobleaching revealed that 1321N1 cells are poorly dye-coupled and do not propagate ICW. Forced expression of Cx43 in 1321N1 cells (which did not show functional hemichannels) increased dye coupling and allowed short-range ICW transmission that was mainly mediated by intercellular diffusion of Ca ²⁺ generated in the stimulated cells. Astrocytoma clones expressing each of the P2YR subtypes were also able to propagate ICWs that were likely dependent on IP₃ generation. These waves exhibited properties particular to each P2YR subtype. Co-expression of eGFP-hCx43 and P2Y ₁R modified the properties of P2Y₁R-generated ICW to those characteristics of P2Y₂R. Increased coupling in P2Y₄R clones induced by expression of eGFP-hCx43 abolished the ICWs observed in uncoupled P2Y₄R clones. No changes in the behavior of ICWs generated in P2Y₂R clones were observed after forced expression of Cx43. These data indicate that in 1321N1 cells gap junctional communication provides intercellular integration of Ca²⁺ signals generated by P2YR activation, thus coordinating the propagation of intercellular calcium waves.