Purinergic Junctional Transmission and Propagation of Calcium Waves in Spinal Cord Astrocyte Networks

Micro-photolithographic methods have been employed to form discrete patterns of spinal cord astrocytes that allow quantitative measurements of Ca2+ wave propagation. Astrocytes were confined to lanes 20–100 μm wide and Ca2+ waves propagated from a point of mechanical stimulation or of application of adenosine triphosphate; all Ca2+ wave propagation was blocked by simultaneous application of purinergic P2Y1 and P2Y2 antagonists. Stimulation of an astrocyte at one end of a lane, followed by further stimulation of this astrocyte, gave rise to Ca2+ transients in the same astrocytes; however, if the second stimulation was applied to an astrocyte at the other end of the lane, then this gave rise to a different but overlapping set of astrocytes generating a Ca2+ signal. Both the amplitude and velocity of the Ca2+ wave decreased over 270 μm from the point of initiation, and thereafter remained, on average, constant with random variations for at least a further 350 μm. Also, the percentage of astrocytes that gave a Ca2+ transient decreased with distance along lanes. All the above observations were quantitatively predicted by our recent theoretical model of purinergic junctional transmission, as was the Ca2+ wave propagation along and between parallel lanes of astrocytes different distances apart. These observations show that a model in which the main determinants are the diffusion of adenosine triphosphates regeneratively released from a stimulated astrocyte, together with differences in the properties and density of the purinergic P2Y receptors on astrocytes, is adequate to predict a wide range of Ca2+ wave transmission and propagation phenomena.