Simulated effect of reduced I_K1 on cardiac action potentials. (a) Model of rabbit ventricular action potential under baseline conditions ([K⁺]_O 4.5 meq/l, dashed line); 50% reduction in I_K1 conductance (solid line); and 50% reduction in I_K1 conductance and [K⁺]_O = 2.9 meq/l (dotted line). (b) Reduction in [K⁺]_O and I_K1 conductance resulted in spontaneous action potentials (*) and DADs (**) that did not reach threshold for action potential generation. Basic cycle length of stimulation was 1,000 ms. (c) Spontaneous action potentials and DADs seen in b were eliminated by a reduction in the amplitude of the Na⁺/Ca²⁺ exchanger.