TABLE I.
Parameters Used in Modeling Action Potentials
| Parameter/Units | Previously used values (Cannon et al., 1993) | Our values |
|---|---|---|
| αm/ms−1 | .288 | 1.0 |
| βm/ms−1 | 1.38 | 2.0 |
| Midpoint of NaCh activation/mV | −40 | −37 |
| Kαm/mV | 10 | 10 |
| Kβm/mV | 18 | 18 |
| αh/ms−1 | .0081 | .0081 |
| βh/ms−1 | 4.38 | 8.0 |
| Midpoint of NaCh inactivation/mV | −80 | −73 |
| Kαh/mV | 14.7 | 14.7 |
| Kβh/mV | 9 | 9 |
| αn/ms−1 | .0131 | .020 |
| βn/ms−1 | .067 | .067 |
| Midpoint of K activation/mV | −23.7 | −39.3 |
| Kαh/mV | 7 | 7 |
| Kβh/mV | 40 | 40 |
| Leak conductance/mS/cm2 | .75 | .25 |
| Maximum Na conductance/mS/cm2 | 150 | 500 |
| Midpoint of NaCh slow inactivation/mV | No slow inactivation | −87 |
| Slope of slow inactivation/mV | – | 9.8 |
| Maximum K conductance/mS/cm2 | 21.6 | 30 |
| Resting potential (Rm)/mV | −85 | −85 |
| Total conductance at Rm/mS/cm2 | 2 | .25 |
| ENa/mV | 48 | 40 |
| EK/mV | −95 | −85 |
| Internal resistivity/Ωcm | Not a cable model | 185 |
Note, we report the midpoint of NaCh channel activation and inactivation and K channel activation rather than the values for the voltage dependence of the parameters m, h, and n as was done previously. This was done to make it easier to compare modeled data to values recorded from real muscle fibers. Internal resistivity was taken from Farnbach and Barchi (1977). Data for slow inactivation was taken from Rich and Pinter (2003). For our modeling, we used values for specific membrane resistance (4,000 Ωcm2 = .25 mS/cm2), slow inactivation (h infinity midpoint −87 mV, slope 9.8 mV) based on previous studies (Kirsch and Anderson, 1986; Featherstone et al., 1996; Rich et al., 1998; Rich and Pinter, 2001, 2003; Vilin et al., 2001). For fast inactivation and activation we used midpoints of −73 and −37 mV based on our previous measures at a holding potential of −110 mV (Rich and Pinter, 2003).