Pharmacological properties of P2 receptors on rat otic parasympathetic ganglion neurons

Abstract

To elucidate the pharmacological profile of P2X receptors and the probable expression of P2Y receptors in otic ganglion neurons from 17-day-old rats, single neurons were enzymatically isolated and maintained in tissue culture for up to 30 h. Whole-cell voltage-clamp recording was carried out at a holding potential of − 60 mV. Most otic ganglion neurons responded to adenosine 5′-triphosphate (ATP), 2-methylthio ATP (2-MeSATP) and α,β-methylene ATP (αβ-meATP) with sustained currents and EC 50 values of 19 µM, 47 µM and 94 µM, respectively. 2′,3′- O-trinitrophenyl-ATP (TNP-ATP) inhibited the response to αβ-meATP and ATP with an IC 50 values of 3.9 nM and 18.3 nM, respectively, which was closed to that observed in nodose neurons. The response to ATP was antagonized by suramin and cibacron blue. The dose–response curve of suramin against ATP response at a pH of 6.5 was shifted to the left compared to that at a pH of 7.4. Diinosine pentaphosphate (Ip 5I), which blocks P2X 3, but not P2X 2/3-mediated responses, had no effect on the currents evoked by ATP or αβ-meATP. In some neurons, uridine 5′-triphosphate (UTP) induced a tiny, but long-lasting current with a mean amplitude of 0.034 ± 0.011 nA. Reverse transcriptase-polymerase chain reaction (RT-PCR) confirmed the expression of mRNAs for P2X 2, P2X 3, P2X 4, P2X 6 and P2X 7, but not for P2X 1 and P2X 5 receptors in otic ganglion. In conclusion, in rat otic ganglion neurons, P2X 2/3 heteromultimer receptors dominate, but P2X 7 and P2Y 2 or P2Y 4 receptors also play roles.