 Solution

Fast ion-channel inactivation would reduce the outward potassium electric current just when it normally repolarizes the axon. Since $C_m{\dot{V}}_m=I_{\mathrm{applied}}-I_{\mathrm{Na}}-I_K-I_{\mathrm{leak}}$, a reduction of positive $I_K$ makes the falling slope less negative. With other mechanisms unchanged, the action potential is generally broader and its after-hyperpolarization is weaker. A plateau or slow return is possible until sodium ion-channel inactivation, leakage, or another outward conductance restores the resting membrane potential. The precise trace depends on those remaining currents; rapid potassium inactivation alone does not determine a unique waveform.

The left panel is a qualitative sketch of this comparison, not a fit or a reconstruction of the missing historical recording.