Effects of tetrodotoxin (TTX) on STIM1-associated calcium transients and the formation of nascent filopodia. (A) Sample illustration of a dendrite at four time-points, 10 s apart, from top to bottom, showing calcium transients (green), associated with STIM1 puncta (red) in EBFP-transfected neuron (blue), recorded in TTX. Some calcium transients in the dendrite are associated with filopodia outgrowth (arrowheads). (B) The number of calcium transients during 5 min per standard segment is measured in control and TTX (n = 20 fields, seven cells for each). (C) Averaged duration of events (n = 40 events, 20 fields for each) scale = secs. (D) Averaged amplitude of events (n = 40 events, 20 fields for each). (E) All related to filopodia outgrowth: new filopodia per 30 min per standard segment, associated with STIM1 puncta and calcium transients (n = 40 fields, seven cells for each). (F) Percent of new filopodia associated with STIM1, of total new filopodia per standard field (n = 40 fields). (G) Averaged persistence of new filopodia in time (seconds; n = 55 protrusions for each). *Significant, 0.05 > p > 0.01; ***highly significant, p < 0.001; n.s., not significant, p ≥ 0.05.