FIGURE 6.

Simulations of impulse responses of bipolar cells and rod photoreceptors. (A) Simulation of bipolar cells with parameters listed in Table 2. The reversal potential of the hyperpolarization-activated channel, E_h, is −75 mV. Since the simulation is restricted to voltage ranges <−50 mV, depolarization-activated K⁺ channels are not included in the model. Impulse responses for bipolar cells, estimated as described in Methods, contain no undershoot, even though the impulse responses are speeded by the activation of the hyperpolarization-activated channel. (B) Simulation of rod photoreceptors. The same set of parameters in Table 2 was used, except that time constant of the hyperpolarization-activated channel conductance is 10 times slower than that for bipolar cells and its reversal potential E_h is −20 mV. Impulse responses for rod photoreceptors contain pronounced undershoots near and below resting potential.