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

Abstract

In order to elucidate the mechanisms of purinergic transmission of calcium (Ca2+) waves between microglial cells, we have employed micro-photolithographic methods to form discrete patterns of microglia that allow quantitative measurements of Ca2+ wave propagation. Microglia were confined to lanes 20-100 μm wide and Ca2+ waves propagated from a point of mechanical stimulation, with a diminution in amplitude, for about 120 μm. The number of cells participating in propagation also decreased over this distance. Ca2+ waves could propagate across a cell-free lane from one microglia lane to another if this distance of separation was less than about 60 μm, indicating that propagation involved diffusion of a chemical transmitter. This transmitter was identified as ATP since all Ca2+ wave propagation was blocked by the purinoceptor antagonist suramin, which blocks P2Y2 and P2Y12 at relatively low concentrations. Antibodies to P2Y12 showed these at very high density compared with P2Y2, indicating a role for P2Y12 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. © Springer Science+Business Media B.V. 2007.