Figure 6. Changes in [Ca²⁺]_i (top) and I_Ca (bottom) elicited by trains of voltage pulses.

Three trains of ten 100 ms voltage pulses were applied at 30 s intervals. These trains were followed by a 3 min resting period after which the same stimulation protocol was repeated. I_Ca (superposition of ten traces) corresponding to the first and third trains in each triplet is shown. Note the decrease in the amplitude of the [Ca²⁺]_i response within the triplet of voltage trains and its partial restoration following the 3 min resting period (indicated by double-headed arrows). The magnitude of I_Ca in each burst showed the ‘negative staircase’ phenomenon.