Expression of the P2Y(1) nucleotide receptor in chick muscle: Its functional role in the regulation of acetylcholinesterase and acetylcholine receptor

In vertebrate neuromuscular junctions, ATP is stored at the motor nerve ter minals and is co-released with acetylcholine during neural stimulation. Her e, we provide several lines of evidence that the synaptic ATP can act as a synapse-organizing factor to induce the expression of acetylcholinesterase (AChE) and acetylcholine receptor (AChR) in muscles, mediated by a metabotr opic ATP receptor subtype, the P2Y(1) receptor. The activation of the P2Y1 receptor by adenine nucleotides stimulated the accumulation of inositol pho sphates and intracellular Ca2+ mobilization in cultured chick myotubes. P2Y 1 receptor mRNA in chicken muscle is very abundant before hatching and agai n increases in the adult. The P2Y1 receptor protein is shown to be restrict ed to the neuromuscular junctions and colocalized with AChRs in adult muscl e (chicken, Xenopus, and rat) but not in the chick embryo. In chicks after hatching, this P2Y1 localization develops over similar to3 weeks. Denervati on or crush of the motor nerve (in chicken or rat) caused up to 90% decreas e in the muscle P2Y(1) transcript, which was restored on regeneration, wher eas the AChR mRNA greatly increased. Last, mRNAs encoding the AChE catalyti c subunit and the AChR alpha -subunit were induced when the P2Y(1) receptor s were activated by specific agonists or by overexpression of P2Y(1) recept ors in cultured myotubes; those agonists likewise induced the activity in t he myotubes of promoter-reporter gene constructs for those subunits, action s that were blocked by a P2Y(1) specific antagonist. These results provide evidence for a novel function of ATP in regulating the gene expression of t hose two postsynaptic effectors.