Purinergic junctional transmission and propagation of calcium waves in cultured spinal cord microglial networks

In order to elucidate the mechanisms of purinergic transmission of calcium (Ca 2 + ) waves between microglial cells, we have employed micro-photolithographic methods to form discrete patterns of microglia that allow quantitative measurements of Ca 2 + wave propagation. Microglia were confined to lanes 20–100 μ wide and Ca 2 + waves propagated from a point of mechanical stimulation, with a diminution in amplitude, for about 120 μ . The number of cells participating in propagation also decreased over this distance. Ca 2 + waves could propagate across a cell-free lane from one microglia lane to another if this distance of separation was less than about 60 μ , indicating that propagation involved diffusion of a chemical transmitter. This transmitter was identified as ATP since all Ca 2 + wave propagation was blocked by the purinoceptor antagonist suramin, which blocks P2Y 2 and P2Y 12 at relatively low concentrations. Antibodies to P2Y 12 showed these at very high density compared with P2Y 2 , indicating a role for P2Y 12 receptors. These observations were quantitatively accounted for by a model in which the main determinants are the diffusion of ATP released from a stimulated microglial cell and differences in the dissociation constant of the purinoceptors on the microglial cells.