Figure 2.
Panel A shows the secondary structure of Nav1.4, highlighting four domains each with six transmembrane segments labeled S1 to S6. Stars indicate fluorophore positions. Panel B displays fluorescence signals for domains 1 to 4 during a pulse to minus 10 millivolts, showing that domain 4 is slower compared to the other domains. Panel C compares the fluorescence signal of domain 4 with the sodium current in reverse gradient for a depolarization to minus 10 millivolts, indicating that the sodium current precedes the movement of the voltage-sensing domain of domain 4. The x-axis in both graphs represents time in milliseconds, and the y-axis represents fluorescence or current.
Voltage sensor dynamics and the hinged-lid model of fast inactivation. (A) Secondary structure of Nav1.4 showing the four domains and the six transmembrane segments of each domain. The stars indicate the positions of the fluorophores used to follow the conformational changes of the VSDs. (B) Fluorescence signals of domains I–IV as indicated for a pulse to −10 mV. Notice how slow DIV is compared with the other domains. (C) Comparison of the fluorescence signal of DIV with the sodium current in reverse gradient for a depolarization to −10 mV, showing that the sodium current precedes the movement of VSD of DIV. (C and D modified from Chanda and Bezanilla, 2002).