Figure 5. Contribution of changes in Na⁺ and K⁺ channel time constants on the effects of temperature on spike efficiency and duration.

A. The maximum of Na⁺ inactivation time constant τ_h decreases as temperature increases for the normal model (control; black). For the test group, the maximum of Na⁺ inactivation time constant τ_h is invariant with temperature change (red). B. The Na⁺ entry ratio decreases as a function of temperature for control (black), while the Na⁺ entry ratio increases as a function of temperature when the inactivation time constant of I_Na (τ_h) is fixed. Keeping I_Na activation time constant (τ_m) invariant or I_K activation time constant (τ_n) invariant with temperature reveals effects of temperature on Na⁺ excess entry similar to that in control. C. The half-height spike duration decreases as a function of temperature for the control group (black), while it becomes relatively independent to temperature change when I_Na inactivation time constant, τ_h, is invariant. The test group with invariant τ_m, or τ_n, has similar behavior as that in control group. D. Example membrane potential and I_Na, I_K for 11, 23, and 37°C when the time constant of I_Na inactivation (τ_h) is kept constant. Note that the overlap of Na⁺ and K⁺ currents becomes larger with temperature, which is opposite to the normal situation (see Figure 1B).