Figure 2.
Perturbations in channel gating by cysteine mutations of the putative “high impact” face of Nav1.4 D4/S3. (A) Voltage-activation relations. Currents were elicited from a holding voltage of −140 mV to voltages between −55 and 65 mV in 5-mV increments. Symbols represent normalized whole cell conductances, obtained by dividing peak currents by the driving force. Solid curves are averages of single Boltzmann fits of normalized conductances from individual cells. (B) Fast inactivation. Inactivation time constants (τh) were obtained from fitting the current decay during depolarization measured in Fig. 2 A. A single exponential relaxation was performed for WT and most mutants; a double exponential relaxation for L1433C and G1430C. Only data in the range from −60 to 35 mV are shown. (C) Steady-state inactivation. Inactivation was induced from a holding voltage of −150 mV by a 100-ms conditioning pulse to a voltage between −180 and −30 mV in 10-mV increments. Solid curves are averages of single Boltzmann fits of normalized currents at a test pulse −25 mV from individual cells. (D) Recovery from fast inactivation. A triple pulse protocol, with a holding voltage of −140 mV and test pulses to −25 mV, was used to measure recovery from inactivation at different recovery potentials between −140 and −80 mV in 10-mV increments (or between −150 and −90 mV for G1430C). Recovery time constants (τrcv) were obtained from single exponential fits. Data and typical parameters derived from fits are listed in Table I. For all panels, n ≥ 3.