Steady state inactivation of sodium currents in neonates and adults. A. Top trace shows the inactivation protocol, applied in voltage clamp from a holding potential of −60 mV. A series of hyperpolarising pre-pulses (5 mV increments, 100 ms duration, −100 to −20 mV) were followed by a depolarising step (to −20 mV, 50 ms duration). Lower traces show representative responses from the time period shown in grey (upper trace) are illustrated for neonates and adults. Capacitive currents have been removed. B. Inactivation curves for neonatal (open circles) and adult SDH neurons (filled circles). Steady state inactivation is similar in both groups, however, neonatal currents do not begin to inactivate until slightly more depolarized membrane potentials (* p < 0.05). C. Time constants of inactivation plotted as a function of voltage for neonates (open circles) and adults (filled circles). Neonates displayed greater time constants of inactivation for all voltages between −100 and −40 mV.