ATP facilitates spontaneous glycinergic IPSC frequency at dissociated rat dorsal horn interneuron synapses

1. The ATP action on spontaneous miniature glycinergic inhibitory postsynap tic currents (mIPSCs) was investigated in rat substantia gelatinosa (SG) ne urons mechanically dissociated from the 2nd layer of the dorsal horn in whi ch their presynaptic glycinergic nerve terminals remained intact. 2. ATP reversibly facilitated the frequency of the mIPSCs in a concentratio n-dependent manner without affecting their amplitude distribution. The ATP agonist, 2-methylthioATP (2MeSATP), mimicked the ATP action, while another ATP receptor agonist, alpha beta-methylene-ATP (alpha,beta-meATP), had no e ffect on mIPSCs. 3. The ATP receptor antagonists, suramin (1 x 10(-6) an) and pyridoxal-5-ph osphate-6-azophenyl-2',4'-disulphonic acid (PPADS) (1 x 10(-5) M), complete ly blocked the facilitatory effect of ATP on glycine release (102.0 +/- 11. 2% and 99.3 +/- 16.2%, n = 6, respectively) without altering the current am plitude distributions. 4. N-Ethylmaleimide (NEM), a sulphydryl alkylating agent, suppressed the in hibitory effect of adenosine on mIPSC frequency (111.2, 13.3%, n = 4) witho ut altering the current amplitude distribution. However, ATP still facilita ted the mIPSC frequency (693.3 +/- 245.2%, n = 4) even in the presence of N EM. 5. The facilitatory effect of ATP (1 x 10(-5) M) on mIPSC frequency was not affected by adding 1 X 10(-4) M Cd2+ to normal external solution but was e liminated in a Ca2+-free external solution. 6. These results suggest that ATP enhances glycine release from nerve termi nals, presumably resulting in the inhibition of SC: neurons which conduct n ociceptive signals to the CNS. This presynaptic PBX-type ATP receptor may f unction to prevent excess excitability in SG neurons, thus preventing an ex cessive pain signal and/or SG cell death.