Fig. 4

Results of FM imaging system in cultured hippocampal neurons. a, c Synaptic boutons of hippocampal neurons stained by FM1-43 dye in a loading process which consisted in 2 min of stimulation with 70 mM [K⁺ ] and subsequent washing. The presence of numerous puncta of fluorescence that appear to be lined up along the neurites result from localized internalization of the dye and are not washed out. b Synaptic boutons destained after a stimulation pulse of 5 s with 70 mM [K⁺]-enriched solution or d with MCM. Note the marked decrease in fluorescence intensity of most of the puncta visible in a and c. Scale bar is 5 μm and applies to all frames e Normalized destaining curves of FM dye loaded synapses upon stimulation with high K⁺ and f MCM. FM dye release curves of all single synapses were fitted mono-exponentially. g Amplitude (ΔF) and h τ were measured from monoexponential fitting curves obtained by depolarization and MCM, and plotted. Data represent average values of 6 (70 mM [K⁺ ]) and 14 (MCM) neurons. **p < 0.01