Two modes of fusion pore opening revealed by cell-attached recordings at a synapse.
Fusion of a vesicle with the cell membrane opens a pore that releases transmitter to the extracellular space. The pore can either dilate fully so that the vesicle collapses completely, or close rapidly to generate 'kiss-and-run' fusion. The size of the pore determines the release rate. At synapses, the size of the fusion pore is unclear, 'kiss-and-run' remains controversial, and the ability of 'kiss-and-run' fusion to generate rapid synaptic currents is questionable. Here, by recording fusion pore kinetics during single vesicle fusion, we found both full collapse and 'kiss-and-run' fusion at calyx-type synapses. For full collapse, the initial fusion pore conductance (G(p)) was usually >375 pS and increased rapidly at > or =299 pS ms(-1). 'Kiss-and-run' fusion was seen as a brief capacitance flicker (<2 s) with G(p) >288 pS for most flickers, but within 15-288 pS for the remaining flickers. Large G(p) (>288 pS) might discharge transmitter rapidly and thereby cause rapid synaptic currents, whereas small G(p) might generate slow and small synaptic currents. These results show that 'kiss-and-run' fusion occurs at synapses and that it can generate rapid postsynaptic currents, and suggest that various fusion pore sizes help to control the kinetics and amplitude of synaptic currents.
He
Liming
L
National Institute of Neurological Disorders and Stroke, 35 Convent Drive, Building 35, Room 2B-1012, Bethesda, Maryland 20892, USA.
Wu
Xin-Sheng
XS
Mohan
Raja
R
Wu
Ling-Gang
LG
D000818:Animals; D002459:Cell Fusion; D025802:Electric Capacitance; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D018698:Glutamic Acid / Q000378:metabolism; D007700:Kinetics; D008561:Membrane Fusion / Q000502:physiology*; D017729:Presynaptic Terminals / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013569:Synapses / Q000378:metabolism*; D013572:Synaptic Vesicles / Q000378:metabolism
D018698:Glutamic Acid