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

Max R. Bennett ^*, Vlado Buljan ^*, Les Farnell  and William G. Gibson 

^* The Neurobiology Laboratory, Institute for Biomedical Research, Department of Physiology, The School of Mathematics and Statistics, The University of Sydney, New South Wales, Australia

Correspondence: Address reprint requests to Max R. Bennett, Tel.: 61-2-9351-2034; E-mail: maxb{at}physiol.usyd.edu.au.

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.

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