Figure 4.

Slow Ca²⁺ signal is observed in muscle fibers directly stimulated by the nerve. A nerve muscle preparation of an EDL muscle was loaded with Fluo3 -AM. The stimulation was performed by a pipette directly trough the nerve as illustrated in the schema (top left). In the right panel, we can see the fluorescence images of the muscle before, during, and after the stimulation through its nerve at 20 Hz for 600 ms. Application of the stimulus is indicated by time = 0 s. Each photograph had a scanning time of 1.57 s with no delay between them. We can see that after the end of tetanus, the fibers took several seconds to return to basal fluorescence levels as in the case for isolated fibers. In the graph at left, the average of four Ca²⁺ signals (filled squares) and the inhibition of the slow component obtained after incubation of nerve muscle preparation for 30 min with 20 µM of XeB (empty squares) are shown. The relative fluorescence levels are normalized to the maximum value obtained for each case.