ATP modulation of synaptic transmission in the spinal substantia gelatinosa

Actions of adenosine triphosphate (ATP) on neurons of the substantia gelatinosa (SG) were evaluated in spinal cord slices using tight-seal, whole-cell recordings. Bath-applied ATP activated a fast inward current and potentiated both glutamate-induced and synaptically evoked currents by acting through a purinergic receptor with the pharmacology of the P2 type. ATP also induced a delayed slow outward current and depressed synaptic currents that appeared to result from hydrolysis of ATP to adenosine. The inhibitory actions had features suggesting mediation by a P1-like purinergic receptor. Suramin, a putative P2 antagonist, inhibited ATP-induced fast inward currents but did not suppress synaptic currents evoked by dorsal root stimulation. It was concluded that in the SG, ATP released in synaptic regions acts as a synaptic modulator by augmenting excitatory amino acid actions and possibly by also producing a secondary adenosine inhibition.