Figure 5. Fhf2^KO strands are susceptible to conduction failure with reduction in gNa_V and elevated temperatures.

(A) In Fhf2^WT strand, a 78% reduction in sodium conductance leads to diminished action potential (AP) amplitude and slowed conduction velocity, but no block is observed. (B) In Fhf2^KO strand, a 32% reduction in sodium conductance leads to progressive decay in AP amplitude, and conduction block. (C) [dV/dt]max for Fhf2^WT and Fhf2^KO strands plotted versus reductions in gNa_V. For each strand, [dV/dt]max declines as gNa_V decreases until point of failure. (D) Safety factor for Fhf2^WT and Fhf2^KO strands plotted versus reductions in gNa_V. SF declines as gNa_V decreases until point of failure. (E) Conduction velocity for Fhf2^WT and Fhf2^KO strands plotted versus reductions in gNa_V. For each strand, CV declines as gNa_V decreases until point of failure. (F) The Fhf2^WT strand faithfully conducts action potentials when temperature is increased to 45°C. (G) The Fhf2^KO strand fails to conduct at 41°C due to faster rates of open and closed state inactivation. (H) Conduction velocity for Fhf2^WT and Fhf2^KO strands plotted versus rising temperature. CV increases with temperature in the Fhf2^WT strand, while decreasing in the Fhf2^KO strand until failure temperature.