• M D Baker and H Bostock.
• Sobell Department of Neurophysiology, Institute of Neurology, London, United Kingdom.
• J. Neurophysiol. 1997 Mar 1; 77 (3): 1503-13.

AbstractDorsal root ganglion neurons from adult rats (> or = 200 g) were maintained in culture for between 1 and 3 days. Membrane currents generated by large neurons (50-75 microns apparent diameter) were recorded with the whole cell patch-clamp technique. Large neurons generated transient Na+ currents and at least two types of inward current that persisted throughout 200-ms voltage-clamp steps to +20 mV. One persistent current activated close to -35 mV (high threshold), whereas in about half of the cells another persistent current began to activate negative to -70 mV (low threshold). The high-threshold persistent current was identified as a Ca2+ current, as previously described in these neurons. The low-threshold current was reversibly suppressed either by replacing external Na+ with tetramethylammonium ions or by reducing external Na+ concentration ([Na+]) and simultaneously raising external [Ca2+]. It was blocked by tetrodotoxin (TTX) with an apparent equilibrium dissociation constant in the single nanomolar range. We conclude that the low-threshold current is a TTX-sensitive, persistent Na+ current. The persistent TTX-sensitive current contributed to steady-state membrane current from at least -70 mV to 0 mV, a wider potential range than predicted by activation-inactivation gating overlap for transient Na+ current. Because of its low threshold and fast activation kinetics, the persistent Na+ current is expected to play an important role in determining membrane excitability.

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