Long-term spontaneous membrane currents in DRG neurons

We have experimented with freshly isolated single DRG neurons from neonatal (P0-5) rats to study currents mediated by voltage dependent Na⁺ (Nav) channels. All experiments were performed using the whole-cell mode of patch-clamp electrophysiology and following the standard steps of this technique. However, in a subgroup of neurons, spontaneous events resembling neurotransmitter release were observed under conditions optimized for whole-cell patch-clamp recordings of I_Na. All events have a fast rise phase (similar to responses of receptor channels), but decay in a heterogeneous manner. The waveform of the event closely matches that of the response of the purinergic receptor P2X type to ATP. This new activity in neurons was observed at -60 mV and was facilitated during relatively strong hyperpolarization. Although spontaneous fluctuations, termed membrane potential instabilities, are described in DRG neurons, the observed inward currents at more hyperpolarized states are distinct and novel. The spontaneous heterogeneous activities could be relevant to the elucidation of pain mechanisms by distinct pharmacological tools.