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ϩ channel) mRNA, and the expression of these three proteins was confirmed by immunocytochemistry in mSCG neurons. I RIL was enhanced by zinc, inhibited by barium and fluoxetine, but unaffected by quinine and ruthenium red, strongly suggesting that it was carried through TREK-1/2 channels. Consistently, a channel with properties identical with the heterologously expressed TREK-2 was recorded in most (75%) cell-attached patches. These results provide the first evidence for the expression of K2P channels in the mammalian autonomic nervous system, and they extend the impact of these channels to the entire nervous system.

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Non-adapting superior cervical ganglion (SCG) neurones with a clustering activity and sub-threshold membrane potential oscillations were occasionally recorded, suggesting the presence of a persistent sodium current (I(NaP)). The perforated-patch technique was used to establish its properties and physiological role. Voltage-clamp experiments demonstrated that all SCG cells have a TTX-sensitive I(NaP) activating at about -60 mV and with half-maximal activation at about -40 mV. The mean maximum I(NaP) amplitude was around -40 pA at -20 mV. Similar results were achieved when voltage steps or voltage ramps were used to construct the current-voltage relationships, and the general I(NaP) properties were comparable in mouse and rat SCG neurons. I(NaP) was inhibited by riluzole and valproate with an IC(50) of 2.7 and 3.8 microM, respectively, while both drugs inhibited the transient sodium current (I (NaT)) with a corresponding IC(50) of 34 and 150 microM. It is worth noting that 30 microM valproate inhibited the I(NaP) by 70% without affecting the I(NaT). In current clamp, valproate (30 microM) hyperpolarised resting SCG membranes by about 2 mV and increased the injected current necessary to evoke an action potential by about 20 pA. Together, these results demonstrate for the first time that a persistent sodium current exists in the membrane of SCG sympathetic neurones which could allow them to oscillate in the sub-threshold range. This current also contributes to the resting membrane potential and increases cellular excitability, so that it is likely to play an important role in neuronal behaviour.