Amino acid variations resulting in functional and nonfunctional zebrafish P2X1 and P2X5.1 receptors

摘要

Several zebrafish P2X receptors (zP2X1, zP2X2, and zP2X5.1) have been reported to produce little or no current although their mammalian orthologs produce functional homomeric receptors. We isolated new cDNA clones for these P2X receptors that revealed sequence variations in each. The new variants of zP2X1 and zP2X5.1 produced substantial currents when expressed by Xenopus oocytes, however the new variant of zP2X2 was still nonfunctional. zP2X2 lacks two lysine residues essential for ATP responsiveness in other P2X receptors; however introduction of these two lysines was insufficient to allow this receptor to function as a homotrimer. We also tested whether P2X signaling is required for myogenesis or synaptic communication at the zebrafish neuromuscular junction. We found that embryonic skeletal muscle expressed only one P2X receptor, P2X5.1. Antisense knockdown of P2X5.1 eliminated skeletal muscle responsiveness to ATP but did not prevent myogenesis or behaviors that require functional transmission at the neuromuscular junction.