Activation of ATP receptor increases the cytosolic Ca(2+) concentration in nucleus accumbens neurons of rat brain

Physiology and pathophysiology of purinergic neurotransmission

This review is focused on purinergic neurotransmission, i.e., ATP released from nerves as a transmitter or cotransmitter to act as an extracellular signaling molecule on both pre- and postjunctional membranes at neuroeffector junctions and synapses, as well as acting as a trophic factor during development and regeneration. Emphasis is placed on the physiology and pathophysiology of ATP, but extracellular roles of its breakdown product, adenosine, are also considered because of their intimate interactions. The early history of the involvement of ATP in autonomic and skeletal neuromuscular transmission and in activities in the central nervous system and ganglia is reviewed. Brief background information is given about the identification of receptor subtypes for purines and pyrimidines and about ATP storage, release, and ectoenzymatic breakdown. Evidence that ATP is a cotransmitter in most, if not all, peripheral and central neurons is presented, as well as full accounts of neurotransmission and neuromodulation in autonomic and sensory ganglia and in the brain and spinal cord. There is coverage of neuron-glia interactions and of purinergic neuroeffector transmission to nonmuscular cells. To establish the primitive and widespread nature of purinergic neurotransmission, both the ontogeny and phylogeny of purinergic signaling are considered. Finally, the pathophysiology of purinergic neurotransmission in both peripheral and central nervous systems is reviewed, and speculations are made about future developments.

Cellular Distribution and Functions of P2 Receptor Subtypes in Different Systems

This review is aimed at providing readers with a comprehensive reference article about the distribution and function of P2 receptors in all the organs, tissues, and cells in the body. Each section provides an account of the early history of purinergic signaling in the organ?cell up to 1994, then summarizes subsequent evidence for the presence of P2X and P2Y receptor subtype mRNA and proteins as well as functional data, all fully referenced. A section is included describing the plasticity of expression of P2 receptors during development and aging as well as in various pathophysiological conditions. Finally, there is some discussion of possible future developments in the purinergic signaling field.

P2 receptor modulation and cytotoxic function in cultured CNS neurons

In this study we investigate the presence, modulation and biological function of P2 receptors and extracellular ATP in cultured cerebellar granule neurons. As we demonstrate by RT-PCR and western blotting, both P2X and P2Y receptor subtypes are expressed and furthermore regulated as a function of neuronal maturation. In early primary cultures, mRNA for most of the P2 receptor subtypes, except P2X(6), are found, while in older cultures only P2X(3), P2Y(1) and P2Y(6) mRNA persist. In contrast, P2 receptor proteins are more prominent in mature neurons, with the exception of P2Y(1). We also report that extracellular ATP acts as a cell death mediator for fully differentiated and mature granule neurons, for dissociated striatal primary cells and hippocampal organotypic cultures, inducing both apoptotic and necrotic features of degeneration. ATP causes cell death with EC(50) in the 20-50 microM range within few minutes of exposure and with a time lapse of at most two hours. Additional agonists for P2 receptors induce toxic effects, whereas selected antagonists are protective. Cellular swelling, lactic dehydrogenase release and nuclei fragmentation are among the features of ATP-evoked cell death, which also include direct P2 receptor modulation. Comparably to P2 receptor antagonists previously shown preventing glutamate-toxicity, here we report that competitive and non-competitive NMDA receptor antagonists inhibit the detrimental consequences of extracellular ATP. Due to the massive extracellular release of purine nucleotides and nucleosides often occurring during a toxic insult, our data indicate that extracellular ATP can now be included among the potential causes of CNS neurodegenerative events.

Synaptic P2X receptors

Over the past two years, ATP has clearly been shown to act as a co-transmitter with GABA, glycine and probably glutamate in the central nervous system. Our understanding of the ATP-gated P2X receptors is progressing rapidly, and the pharmacology, stoichiometry and subunit combinations of heteropolymeric P2X channels has been substantially elucidated.