Extracellular ATP activates ERK1/ERK2 via a metabotropic P2Y1 receptor in a Ca2+ independent manner in differentiated human skeletal muscle cells

ATP is released at the neuromuscular junction to regulate development and proliferation. The sequential expression of P2X and P2Y receptors has been correlated to these effects in many species and cell lines. We have therefore investigated ATP mediated signalling in differentiated primary human skeletal muscle cells. ATP was capable to trigger Ca2+ transients in these cells via P2Y receptors which were not attributable to Ca2+, influx via P2X receptors. Instead, ATP propagated the formation of inositol phosphate (IP) with an EC50 of 21.3 mu M. The Ca2+, transient provoked by ATP was abrogated roughly 75% by the phospholipase C (PLC) inhibitor, U73122. Interestingly, the ryanodine sensitive Ca2+ pool was not involved in ATP triggered Ca2+ release. On mRNA level and by a pharmacological approach we confirmed the presence of the P2Y(1), P2Y(2), P2Y(4) and P2Y(6) receptors. Substantially, ATP activated IP formation via a P2Y, receptor. In addition, ATP elicited extracellular signal regulated kinase (ERK)1/2 phosphorylation in a time and concentration dependent manner, again mainly via P2Y, receptors. The ATP mediated ERK1/2 phosphorylation was strictly dependent on phospholipase C and P13 kinase activity. Importantly, ATP mediated ERK1/2 phosphorylation. was Ca2+ independent. This observation was corroborated by the finding that conventional protein kinase C inhibitors did not Suppress ATP triggered ERK1/2 phosphorylation. Taken together, these observations highlight the importance of ATP as a co-neurotransmitter at the neuromuscular junction via dual signalling, i.e. IP3 receptor mediated Ca2+, transients and Ca2+, insensitive phosphorylation of ERK1/2. (c) 2006 Elsevier Inc. All rights reserved.