Fig. 2.

Intracellular calcium transients induced by action potential stimulation of different frequencies were measured in the cell body of DRG neurons with confocal microscopy and the ratiometric calcium indicator indo-1. Individual cytoplasmic calcium spikes (B, D–F) can be seen in response to individual action potentials (arrows) elicited by electrical stimulation at different frequencies. Stimulation at higher frequencies resulted in temporal summation and an elevation in intracellular calcium level that was positively correlated with the stimulus frequency and sustained for the period of the stimulus train (A–D). In response to higher frequency stimulation, individual calcium spikes (arrows) could be resolved using single line-scan mode confocal microscopy on top of a large increase in intracellular calcium concentration (G). Note the difference in axis scaling for each graph.