Regulation Of The Fusion Pore Kinetics

The most important function of the neuron and neuroendocrine cells were releasetheir transmitters when the action potential arrive in and trigger the calcium influxthrough the voltage gated calcium channel. Presynaptic vesicle can fuse to plasmamembrane via two alternative modes: full fusion and 'kiss-and-run'. Full fusionoccurs when the vesicle and plasma membranes merge and all the contents arereleased. 'Kiss-and-run' releases vesicle contents through a transient fusion pore.The 'Kiss-and-run' mechanism allows partial release during a release event bylimiting the open time of the fusion pore. Both vesicle release probability and theswitch between full fusion and 'kiss-and-run' are subject to presynaptic modulationin synaptic transmission. Modulation of presynaptic release probability has beenintensively investigated. However, little is known about the switch between fullfusion and 'kiss-and-run'.Glial cells, including astrocytes, oligodendrocytes and Schwann cells, havebeen generally considered as passive components in the nervous system. Recentlyemerging evidence indicates that astrocytes, by releasing signaling moleculesincluding glutamate and ATP, may also play active roles in various neural functionsincluding neurogenesis, synaptogenesis, and synaptic modulation and plasticity.However, the mechanisms by which glial cells release transmitters have not yet beendetermined.Combining the amperometric recording, membran capacitance recording, FMsingle vesicle imaging, and immunochemistry, we studied the GPCR activationeffect on the switch between full fusion and kiss-and-run mode in rat adrenalchromaffin cells (RACCs). We also studied the exocytosis mode of the glutamatevesicle in astrocyte under different stimulate condition. We found that (1)Endogenous transmitters, such as ATP, opioids peptide, and somatostatin, canactivated their auto-receptor, releasing Gβγ subunits, which directly interacted withSNARE complex and then reduce the open time of the fusion pore in RACCs.Paralle activated Gαq pathway removes the ATP effect on the open time of the fusionpore via PKC activation.(2) In astrocyte, combining immunochemistry and FM single vesicle imaging,we defined a group of large glutamate vesicle (1000 folds of the volume of thetypical synaptic vesicle). Underlying the physiological stimulation, the glialglutamate vesicle release only 10% of their content via kiss-and-run mode.Taken together, our results demonstrated that GPCR activation could modulatethe synaptic transmittion efficiency via switch between full fusion and kiss-and-run.Kiss-and-run exocytosis not only existed in the neuron and neuroendocrine cells, butalso in the astrocyte. The kiss-and-run mode exocytosis was very useful to limited torelease amount under the physiological condition. Our work was important forunderstanding the molecular difference between the full fusion and kiss-and-runexocytosis. The work on astrocyte will help us to have a better understanding of thefunctional difference of astrocyte under the physiological and pathologicalconditions.