Purine neuromodulators

The endogenous purine mediator adenosine, originating from adenosine 5-triphosphate (ATP), is a widely distributed neuromodulator with complex effects (Sawynok, 1998 Sawynok and Liu, 2003). Four adenosine receptors have been identified and are termed Al, A2A, A2B, and A3 (Fredholm et al., 2001). They are all GPCRs and couple to classical second messenger pathways Al and A3 receptor activation decreases the level of cAMP, A2 increases it, whereas A2B receptor stimulates PLC (Sawynok, 1998 Sawynok and Liu, 2003). 

Overall, the lack of in vivo methods available for the separation and detection of purine molecules has led to a deficiency in the fundamental understanding of how they function as neiuotransmitters and/or neuromodulators. Since the long-standing view was that purine molecules were mainly intracellular signaling regulators, few techniques have pushed for the sensitive quantification of the extracellular concentration of these molecules to elucidate how they behave as a neurotransmitters [166]. With the advent of improved column technologies and detection methods, such as BDD electrodes, the potential of making routine extracellular purine measurements may become a reality. 

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