P2X(2), P2X(2-2) and P2X(5) receptor subunit expression and function in rat thoracolumbar sympathetic neurons

The present study investigated the pharmacological properties of excitatory P2X receptors and P2X(2) and P2X(5) receptor subunit expression in rat-cul tured thoracolumbar sympathetic neurons. In patch-clamp recordings, ATP (3- 1000 LM; applied for 1 s) induced inward currents in a concentration-depend ent manner. Pyridoxal-phosphate-6-azophenyl-2',4'-disulfonate (PPADS; 30 mu m) counteracted the ATP response. In contrast to ATP, alpha,beta -meATP (30 mum; for 1 s) was virtually ineffective. Prolonged application of ATP (100 mum; 10 s) induced receptor desensitization in a significant proportion of sympathetic neurons in a manner typical for P2X(2-2) splice variant-mediat ed responses. Using single-cell RT-PCR, P2X(2), P2X(2-2) and P2X(5) mRNA ex pression was detectable in individual tyrosine hydroxylase-positive neurons ; coexpression of both P2X(2) isoforms was not observed. Laser scanning mic roscopy revealed both P2X(2) and P2X(5) immunoreactivity in virtually every TH-positive neuron. P2X(2) immunoreactivity was largely distributed over t he cell body, whereas P2X(5) immunoreactivity was most distinctly located c lose to the nucleus. In summary, the present study demonstrates the express ion of P2X(2), P2X(2-2) and P2X(5) receptor subunits in rat thoracolumbar n eurons. The functional data in conjunction with a preferential membranous l ocalization of P2X(2)/P2X(2-2) compared with P2X(5) suggest that the excita tory P2X responses are mediated by P2X(2) and P2X(2-2) receptors. Apparentl y there exist two types of P2X(2) receptor-bearing sympathetic neurons: one major population expressing the unspliced isoform and another minor popula tion expressing the P2X(2-2) splice variant.