Figure 1.
Panel A: Line graph showing sodium current of squid giant axon before (black line) and after pronase treatment (red line). The x-axis represents time in milliseconds, and the y-axis represents current in milliamperes per square centimeter. The initial outward current is a gating current observed because the external solution contained one-fifth sodium. Panel B: Line graph showing gating current for a depolarization to 0 millivolts from minus 140 millivolts. The x-axis represents time in milliseconds, and the y-axis represents current in microamperes per square centimeter. Panel C: Diagram illustrating the model of activation and inactivation, introducing the ball-and-chain model. The diagram includes labeled states and transitions between them, indicating the processes of activation and inactivation. Panel D: Series of diagrams showing different states of the model, labeled with various states and transitions.
Origins of the Ball and Chain model of fast inactivation. (A) Sodium current of squid giant axon before (black) and after pronase treatment (red) for a depolarization to 0 mV from a holding potential of −70 mV. The initial outward current is a gating current observed because the external solution contained 1/5 sodium (modified from Stimers et al., 1985). (B) Gating current for a depolarization to 0 mV from −140 mV, showing the off current for different pulse durations as indicated, returning to −140 mV (modified from Armstrong and Bezanilla, 1977). (C and D) Model of activation and inactivation that introduced the ball and chain model (modified from Armstrong and Bezanilla, 1977).