Figure 3. Effects of stimulus frequency and train length.

A, Ca²⁺ transients evoked at a constant frequency of 10 Hz but with a variable number of stimuli (1, 5, 10, 20, 30 and 50). A change in fluorescence was observed even in response to a single stimulus. Note that significant broadening of the Ca²⁺ transient occurred after 20–50 stimuli. Inspection of the Ca²⁺ transient evoked by 50 stimuli shows that the signal rose rapidly for about 1200 ms before reaching a plateau that was maintained throughout the period of stimulation. The bars indicate the periods of nerve stimulation. B, Ca²⁺ transients evoked by trains of 10 stimuli applied at frequencies of 1, 2, 5, 10, 20 and 50 Hz.