Figure 1.
The currents and kinetic characteristics of voltage-gated sodium (Nav1.5) channels expressed in HEK293.
(A–C) The representative currents of Nav1.5 channels were produced with the voltage protocols placed at the bottom, respectively. (D and E) The G–V curve (D) and channel availability curve (E) were measured from (A) and (B), respectively. Normalized curves were fitted to the Eq. 1 and Eq. 2. For activation, V50 = −34.5±1.5 mV (P<0.001) and k = 7.2±0.6 (n = 14); for steady-state inactivation (availability), V50 = −89.1±1.6 mV and k = 5.5±0.4 (n = 11). Error bars represent S.D.. (F) Time constants are plotted as a function of membrane potentials. The time constants of activation (circle) and inactivation (triangle down) and deactivation (triangle up) were derived from mono-exponential fits to the data shown in (A and C).
Figure 2.
(A) Fractional recovery from inactivation was performed with the voltage protocol in inset. Time constants of recovery are 5.1±0.9 (n = 9), 12.5±2.1 (n = 7), 26.1±3.8 (n = 6) and 47.9±3.4 (n = 6) ms at−120,−110,−100 and−90 mV, respectively. (B–C) Traces were obtained from the same patch at−120 mV with P1 = 30 ms for (B) and P1 = 1000 ms for (C). (D) The fractional recovery curves are plotted for (B) and (C), respectively. The solid lines are fits to the mono-exponential Eq.4 (empty circle) for (B) and the bi-exponential Eq. 5 (solid circle) for (C). (E) The slow inactivation currents were evoked by the voltage protocol with the various P1 durations shown at the bottom. (F) Development of slow inactivation. The solid line is a fit to Eq. 3 with a time constant τ = 1.79±0.11 s (n = 7). For all of cases, P2 = 20 ms.
Figure 3.
(A) The 8-state Model I has three closed states (C1, C2, and C3), four inactivated states (I11–I14) and one open state (O). (B) Model II has four additional slow inactivated states (I21–I24) attached to Model I. The values of parameters in both the models are given in Table 1.
Table 1.
Best fit model parameters.
Figure 4.
Comparison of kinetic characteristics between data and simulations.
Unless otherwise stated, simulation was derived from Model I. (A–C) Fitting the Model I to the data of activation (A), steady-state inactivation (B) and deactivation (C). Black traces represent data and red ones simulations. (D–F) Time constants for activation (D), fast inactivation (E) and deactivation (F) are plotted as a function of voltages. The empty and solid circles represent the data and simulations as indicated. (G) The V50′s values of G–V curves of activation are 34.5 mV for data and−34.0 mV for simulation. (H) The V50′s values of steady-state inactivation are−89.1 mV for data,−89.2 mV for Model I and−89.7 mV for Model II. (I) Fractional recoveries of Nav1.5 were acquired at−120,−110,−100 and−90 mV with P1 = 30 ms and P2 = 20 ms. (J) Time constants of recovery of data and simulation are 5.1 and 5.6, 12.5 and 11.9, 26.1 and 26.6 and 47.9 and 49.6 ms at−120,−110,−100 and−90 mV, respectively.
Figure 5.
Comparison of Slow inactivation and recovery between the data and simulations.
The empty and solid circles represent respectively the data and simulations. (A) Development of slow inactivation. The solid lines are fits to Eq. 3 with the time constants of 1.79 s (data) and 1.58 s (simulation). (B–C) Fitting the Model II to the data shown in Fig 2B–C. Black traces are data and red ones fits. (D) The curves of fractional recovery are plotted for data and simulations in (B) and (C). Square and circle are for P1 = 30 ms in (B) and P1 = 1000 ms in (C).