Fig. 5.

Voltage dependence and development of steady-state slow inactivation for Na_v1.4, Na_v1.4/F1579A and Na_v1.4/Y1586A sodium channels. A, the voltage dependence of slow inactivation was examined using the standard protocol described in Fig. 2C and shown in the inset. Amplitudes of peak transient currents measured during a 20-ms depolarization to −10 mV (Na_v1.4 and Na_v1.4/F1579A) or 0 mV (Na_v1.4/Y1586A) after a 100-s conditioning prepulse from a holding potential (V_hold) of −120 mV to potentials ranging from −90 to 0 mV and a 50-ms hyperpolarization to −120 mV were normalized to the maximum current obtained during the inactivation protocol for that oocyte and plotted as a function of the conditioning potential. Values are means ± S.E. from four to six experiments in separate oocytes; curves are fitted to the Boltzmann equation. B, the development of steady-state slow inactivation was assessed using a two-pulse protocol (see inset) in which oocytes were clamped at a V_hold of −30 mV (Na_v1.4), −35 mV (Na_v1.4/F1579A), or −50 mV (Na_v1.4/Y1586A) and stimulated every minute with a 20-ms test pulse to −10 mV (Na_v1.4 and Na_v1.4/F1579A) or 0 mV (Na_v1.4/Y1586A) that was preceded by a 2-s repolarization to −120 mV. Currents were normalized to peak test pulses elicited from a V_hold of −120 mV before depolarization; values are means ± S.E. from nine experiments in separate oocytes. Curves were fitted with a single-exponential decay function.