Figure 7. Increases in temperature result in a decrease in AHP duration.

A. The action potential demonstrates a large and prolonged afterhyperpolarization (AHP) for low temperature (e.g., T = 18°C), and a smaller and shorter duration AHP for higher temperatures (e.g., T = 36, and 42°C, respectively). B. During an action potential, the ratio of potassium current I_K over I_Na as a function of time shows that there is a large amount of I_K available after the peak of action potential for low temperature (e.g., T = 18°C) in comparison with that at high temperatures (e.g., T = 36, and 42°C, respectively). C. Plot of the amplitude of I_K during action potential generation at different temperatures reveals that increasing temperature results in a marked reduction in the amplitude of I_K, especially 20–60 msec after the spike, but also during the repolarizing phase of the action potential. D. Action potential AHP duration decreases slowly with increases in temperature for temperatures below approximately 37°C, while decreases rapidly for temperatures greater than approximately 37°C. Keeping the time constant of I_K activation (τ_n) invariant abolishes this effect, while keeping the time constants of I_Na activation (τ_m) or inactivation (τ_h) invariant does not, although they do alter the magnitude and temperature range of the effect.