Purinergic receptors activating rapid intracellular Ca²⁺ increases in microglia

We provide both molecular and pharmacological evidence that the metabotropic, purinergic, P2Y₆, P2Y₁₂ and P2Y ₁₃, receptors and the ionotropic P2X₄ receptor contribute strongly to the rapid calcium response caused by ATP and its analogues in mouse microglia. Real-time PCR demonstrates that the most prevalent P2 receptor in microglia is P2Y₆ followed, in order, by P2X₄, P2Y ₁₂, and P2X₇ = P2Y₁₃. Only very small quantities of mRNA for P2Y₁, P2Y₂, P2Y₄, P2X₁₄ P2X₃, and P2X₅. were found. Dose-response curves of the rapid calcium response gave a potency order of: 2MeSADP>ADP=UDP=IDP=UTP>ATP>BzATP, whereas A2P4 had little effect. Pertussis toxin partially blocked responses to 2MeSADP, ADP and UDP. The P2X₄ antagonist suramin, but not PPADS, significantly blocked responses to ATP. These data indicate that P2Y₆, P2Y₁₂, P2Y₁₃ and P2X receptors mediate much of the rapid calcium responses and shape changes in microglia to low concentrations of ATP, presumably at least partly because ATP is rapidly hydrolyzed to ADP. Expression of P2Y₆, P2Y₁₂ and P2Y₁₃ receptors appears to be largely glial in the brain, so that peripheral immune cells and CNS microglia share these receptors. Thus, purinergic, metabotropic, P2Y₆, P2Y₁₂, P2Y₁₃, and P2X₄ receptors might share a role in the activation and recruitment of microglia in the brain and spinal cord by widely varying stimuli that cause the release of ATP, including infection, injury and degeneration in the CNS, and peripheral tissue injury and inflammation which is signaled via nerve signaling to the spinal cord.