Fig. 4.

Depolarization-induced, but not BWSV-induced, FM1-43 staining is blocked at csp mutant NMJs at 32°C. At 32°C K⁺ depolarization failed to induce a significant FM1-43 uptake in synaptic boutons of homozygousshi^ts1 NMJs (A1) and homozygous csp^E16 NMJs (B1). After cooling to 22°C, K⁺ stimulation stained synaptic boutons of shi^ts1 NMJs (A2) with FM1-43 andcsp^E16 NMJs (B2). For the next series of experiments (C, D), the mutant ts block of FM1-43 uptake at 32°C was confirmed with K⁺depolarization for homozygous shi^ts1 NMJs (C1) and homozygous csp^E16NMJs (D1). No staining was observed in either case. The subsequent BWSV stimulation in the presence of external Ca²⁺ at 32°C failed to induce any uptake of FM1-43 dye at shi^ts1 mutant synaptic boutons (C2). However, BWSV stimulation at 32°C induced a strong uptake of FM1-43 dye at csp^E16mutant NMJs (D2). Each series of images represents at least five independent experiments and shows partial NMJs of muscle 6/7 except in D. Scale bars, 50 μm.