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A Quantitative Model of Purinergic Junctional Transmission of Calcium Waves in Astrocyte Networks

M. R. Bennett ^*, L. Farnell  and W. G. Gibson 

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

Correspondence: Address reprint requests to Professor Max Bennett, Neurobiology Laboratory, Dept. of Physiology, University of Sydney, NSW 2006, Australia. Tel.: 61-2-9351-2034; Fax: 61-2-9351-3910; E-mail: maxb{at}physiol.usyd.edu.au.

A principal means of transmitting intracellular calcium (Ca²⁺) waves at junctions between astrocytes involves the release of the chemical transmitter adenosine triphosphate (ATP). A model of this process is presented in which activation of purinergic P2Y receptors by ATP triggers the release of ATP, in an autocrine manner, as well as concomitantly increasing intracellular Ca²⁺. The dependence of the temporal characteristics of the Ca²⁺ wave are shown to critically depend on the dissociation constant (K_R) for ATP binding to the P2Y receptor type. Incorporating this model astrocyte into networks of these cells successfully accounts for many of the properties of propagating Ca²⁺ waves, such as the dependence of velocity on the type of P2Y receptor and the time-lag of the Ca²⁺ wave behind the ATP wave. In addition, the conditions under which Ca²⁺ waves may jump from one set of astrocytes across an astrocyte-free lane to another set of astrocytes are quantitatively accounted for by the model. The properties of purinergic transmission at astrocyte junctions may determine many of the characteristics of Ca²⁺ propagation in networks of these cells.

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