Fig. 1.

Depolarization fails to trigger FM1-43 destaining in csp mutants at 32°C. At 22°C K⁺ stimulation in the presence of FM1-43 induced a punctate FM1-43 staining of synaptic boutons at all NMJs of wild-type (A1), mutant homozygousshi^ts1 (B1), and mutant homozygous csp^E16 (C1) muscles. A subsequent K⁺ stimulation at 32°C completely destained the FM1-43-labeled synaptic boutons of wild-type (A2) and shi^ts1 mutant (B2) NMJs. However, K⁺ stimulation at 32°C failed to destain the FM1-43-labeled synaptic boutons ofcsp^E16 mutant NMJs (C2). After cooling the csp^E16 mutant preparation to 22°C, K⁺ depolarization destained the synaptic boutons (C3) that failed to destain with depolarization at 32°C (C2). Only minute traces of staining could be observed sometimes on large synaptic boutons (arrows). Each series of images (A–C) gives a partial view of the identical NMJ of muscle 6/7 after FM1-43 staining at 22°C (1), after FM1-43 destaining at 32°C (2), and after FM1-43 destaining at 22°C (3). Each series exemplifies at least 10 independent experiments (larvae) for each genotype. Scale bars, 50 μm.