Abstract
A whole-cell sodium-activated outward current has been identified in adult cockroach dorsal unpaired median (DUM) neurones maintained in short-term culture. Superfusion of 100 nM TTX completely blocked the inward current but also reduced the transient outward component without affecting the sustained outward current. Different experimental procedures indicate that TTX effects could not be due to a voltage clamp artefact. Similar effects were obtained when extracellular sodium was replaced with Tris-HCl. The outward current was unaffected by TTX when the membrane was stepped to potential more positive (+60 mV) than sodium reversal potential and the TTX-sensitive outward current amplitude increased in parallel with the sodium inward current at each potential tested. The tail current analysis was used to determine the ionic selectivity of the TTX-sensitive outward current. Tail currents reversed polarity at −95.5 mV (potassium equilibrium potential: −100.5 mV), indicating that sodium-activated outward current was carried mostly by potassium ions.
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