Figure 8.2i Broadening and Accommodation. A Ca²⁺ cell with spontaneous activity was stimulated with depolarizing current. Each spke is wider than the previous one (spike broadening) due to increasing inactivation of the voltage-activated channels that carry the repolarizing K⁺ current. The interval between spikes increases (accommodation) due to a slowly developing outward K⁺ current that counters the depolarizing stimulus. This current also makes the membrane potential hyperpolarize slightly at the end of the stimulus.