Functional expression of P2X 7 receptors in non-neuronal cells of rat dorsal root ganglia

Abstract

The P2X 7 receptor is an ATP-sensitive ligand-gated cation channel, expressed predominantly in cells with immune origin. Recent studies have demonstrated that P2X 7 may play an important role in pain signaling. In the present study, the expression of P2X 7 receptors in non-neuronal cells and neurons isolated from dorsal root ganglia was characterized using patch clamp, pharmacological and confocal microscopy approaches. In small diameter DRG neurons, 100 μM 2′, 3′- O-(4-benzoylbenzoyl)-ATP (BzATP) evoked an inward current, which was inhibited completely by 1 μM A-317491, a potent and selective P2X 3 receptor antagonist. In contrast, BzATP evoked concentration-dependent increases in inward currents in non-neuronal DRG cells with an EC 50 value of 26 ± 0.14 μM, which were resistant to the blockade by A-317491. The activity to evoke cationic currents by P2X receptor agonists in non-neuronal cells showed a rank order of BzATP > ATP > α,β-meATP. Pyridoxal-phosphate-6-azophenyl-,2′,4′-disulphonic acid (PPADS) and Mg 2+ produced concentration-dependent inhibition of BzATP-evoked currents in non-neuronal cells. Confocal microscopy revealed positive immunoreactivity of anti-P2X 7 receptor antibodies on non-neuronal cells. No anti-P2X 7 immunoreactivity was observed on DRG neurons. Further electrophysiological studies showed that prolonged agonist activation of P2X 7 receptors in non-neuronal cells did not lead to cytolytic pore formation. Taken together, the present study demonstrated functional expression of P2X 7 receptors in non-neuronal but not in small diameter neurons from rat DRG. Modulation of P2X 7 receptors in non-neuronal cells might have impact on peripheral sensory transduction under normal and pathological states.