||In vertebrate neuromuscular junctions, adenosine 5'-triphosphate (ATP) is present at the motor nerve terminals, and is co-released with acetylcholine (ACh) during synaptic stimulation. Here, we provide several lines of evidence which suggest that the synaptic ATP could act as a synapse-organizing factor to induce the expression of acetylcholinesterase (AChE) and acetylcholine receptor (AChR) in muscles. The induction of AChE and AChR α-subunit gene expression is mediated by one of the subtypes of ATP receptors, namely P2Y1 purinoceptor. The binding characteristics of [35S]dATPαS on chick muscle membranes resembled to P2Y1 purinoceptors. The activation of P2Y1 purinoceptor, when challenged with agonists, stimulated the accumulation of inositol 1, 4, 5-triphosphates (IP3) and the mobilization of calcium in cultured chick myotubes. The transcript encoding P2Y1 purinoceptor at ~3.2 kb was regulated in chick and rat muscle during development, denervation, regeneration after nerve injury and exercise. The P2Y1 purinoceptor was co-localized with AChR in neuromuscular junction. Lastly, the expression of transcripts encoding AChE and AChR α-subunit was induced when the P2Y1 purinoceptors were activated by specific agonists or by over-expression of P2Y1 purinoceptors in cultured myotubes. These results provided direct evidence to support the novel function of ATP in directing the post-synaptic gene expression.