The Calcium Dependence of Kiss-and-Run Exocytosis at the Crayfish Neuromuscular Junction

Abstract

The classical mode of neurotransmitter release, full collapse fusion (FCF), occurs when a vesicle is completely incorporated into the presynaptic membrane. Growing evidence supports a novel additional mode of neurotransmitter release known as "kiss-and-run" (K&R) in which the vesicle transiently fuses with the membrane, maintaining its basic morphology. In this study we sought to determine whether K&R occurs at the crayfish neuromuscular junction (NMJ) and, if it does exist, whether its prevalence is dependent on the extracellular calcium concentration. We loaded the dye FM1-43 and the fluorescence quencher bromophenol blue (BPB) into synaptic vesicles and looked for a fluorescence increase corresponding to the segregation of FM1-43 from BPB through K&R. We observed K&R at a low extracellular calcium concentration, but it was ambiguous whether K&R occurred at normal extracellular calcium levels. Thus, extracellular calcium appears to play a role in determining the mode of neurotransmitter release.