CHARACTERIZATION OF A P-2X-PURINOCEPTOR IN CULTURED NEURONS OF THE RAT DORSAL-ROOT GANGLIA

1 The electrophysiological actions of the P-2-purinoceptor agonists, a denosine 5'-triphosphate (ATP), 2-methylthio ATP (2-meSATP) and alpha, beta-methyleneATP (alpha,beta-meATP) and of uridine 5'-triphosphate (U TP) were studied under concentration and voltage-clamp conditions in d issociated neurones of 1-6 day old rat dorsal root ganglia. 2 ATP (10 nM-100 mu M) applied rapidly via a U-tube perfusion system (equilibrat ion time <10 ms) activated concentration-dependent inward currents wit h a latency to onset of a few ms, an EC(50) of 719 nM and a Hill slope of 1.47. 3 2-meSATP (10 nM-100 mu M) and alpha,beta-meATP (100nM-100 mu M) also evoked transient inward currents. The EC(50) and Hill slope s were 450 nM and 1.58 for 2-meSATP and 1.95 mu M and 1.53 for alpha,b eta-meATP respectively. There was no significant difference between th e maximum currents evoked by the three agonists. 4 As the concentratio n of ATP increased so the rate of rise and decay of the currents also increased. At 100 and 300 nM ATP the decay of the current was best fit ted by a single exponential, but at 1 mu M and above two exponentials were required. Log-log plots of the rise time or time constants of dec ay versus concentration were linear. Currents evoked by 2-meSATP and a lpha,beta-meATP showed a similar concentration-dependence in their kin etics. 5 Inward currents evoked by ATP, 2-meSATP and alpha,beta-meATP (300 nM) were abolished by the P-2-purinoceptor antagonist, suramin (1 00 mu M). 6 UTP (10 mu M) evoked similar transient inward currents, wh ich were sensitive to suramin (100 mu M). ATP (10 mu M), applied 2 min beforehand, reduced the response to UTP (10 mu M) by 80 +/- 10%. 7 Th is study shows that ATP, 2-meSATP and alpha,beta-meATP act via a suram in-sensitive P-2X-purinoceptor to evoke rapid, transient inward curren ts in dissociated neurones of rat dorsal root ganglia. The pyrimidine nucleotide, UTP, was also active. It is likely that the agonists were acting at the P-2X3-subtype to produce these effects.