Protease activated receptor-1 control of glutamate time course in the synapse cleft

The protease activated receptor-1 (PAR1) is prominently expressed in astrocytes of the central nervous system. Activation of PAR1 increases the ability of synaptically-released glutamate to surmount block by the rapidly unbinding competitive antagonist kynurenic acid. A variety of functional and molecular experiments suggest that this effect does not involve changes in presynaptic glutamate release or postsynaptic AMPA receptor function. Kinetic analysis of native AMPA receptors in outside-out patches allowed the development of a simplified kinetic model of the actions of kynurenic acid. We subsequently used this model to fit the EPSC time course in the absence and presence of kynurenic acid with variable synaptic glutamate concentration profile. The result of this analysis showed that astrocytic G-protein coupled receptor-activation increased the peak synaptic glutamate concentration from 0.96 to 1.72 mM and prolonged the duration of glutamate in the synaptic cleft following PAR1 activation by approximately two-fold. This effect was blocked by selective expression of a PAR1 shRNA in astrocytes. These data suggest that astrocytic G-protein coupled receptors can influence the glutamate concentration time course in the synaptic cleft, which has important implications for excitatory synaptic transmission, as well as synaptic plasticity.