Research paperFunctional ligand-gated purinergic receptors (P2X) in rat vestibular ganglion neurons

The expression of purinergic receptors (P2X) on rat vestibular ganglion neurons (VGNs) was examined using whole-cell patch-clamp recordings. An application of adenosine 5′-triphosphate (ATP; 100 μM) evoked inward currents in VGNs at a holding potential of −60 mV. The decay time constant of the ATP-evoked currents was 2-4 s, which is in between the values for rapidly desensitizing subgroups (P2X1 and P2X3) and slowly desensitizing subgroups (P2X2, P2X4, etc.), suggesting the heterogeneous expression of P2X receptors. A dose-response experiment showed an EC50 of 11.0 μM and a Hill's coefficient of 0.82. Suramin (100 μM) reversibly inhibited the ATP-evoked inward currents. Alpha, beta-methylene ATP (100 μM), a P2X-specific agonist, also evoked inward currents but less extensively than ATP. An application of adenosine 5′-dihosphate (ADP; 100 μM) evoked similar, but much smaller, currents. The current-voltage relationship of the ATP-evoked conductance showed pronounced inward rectification with a reversal potential more positive than 0 mV, suggesting non-selective cation conductance. However, the channel was not permeable to a large cation (N-methyl-d-glucamine) and acidification (pH 6.3) had little effect on the ATP-evoked conductance. RT-PCR confirmed the expression of five subtypes (P2X2-P2X6) in VGNs. The physiological role of P2X receptors includes the modulation of excitability at the synapses between hair cells and dendrites and/or trophic support (or also neuromodulation) from supporting cells surrounding the VGNs.