Changes in the distribution of calcium calmodulin-dependent protein kinase II at the presynaptic bouton after depolarization.
Phosphorylation of synapsin I by CaMKII has been reported to mobilize synaptic vesicles from the reserve pool. In the present study, the distributions of alpha-CaMKII and of synapsin I were compared in synaptic boutons of unstimulated and stimulated hippocampal neurons in culture by immunogold electron microscopy. CaMKII and synapsin I are located in separate domains in presynaptic terminals of unstimulated neurons. Label for alpha -CaMKII typically surrounds synaptic vesicle clusters and is absent from the inside of the cluster in control synapses. In contrast, intense labeling for synapsin I is found within the vesicle clusters. Following 2 minutes of depolarization in high K(+), synaptic vesicles decluster and CaMKII label disperses and mingles with vesicles and synapsin I. These results indicate that, under resting conditions, CaMKII has limited access to the synapsin I in synaptic vesicle clusters. The peripheral distribution of CaMKII around vesicle clusters suggests that CaMKII-mediated declustering progresses from the periphery towards the center, with the depth of penetration into the synaptic vesicle cluster depending on the duration of CaMKII activation. Depolarization also promotes a significant increase in CaMKII immunolabel near the presynaptic active zone. Activity-induced redistribution of CaMKII leaves it in a position to facilitate phosphorylation of additional presynaptic proteins regulating neurotransmitter release.
Tao-Cheng
Jung-Hwa
JH
EM Facility, NINDS, NIH, Bethesda, MD 20892, USA.
Dosemeci
Ayse
A
Winters
Christine A
CA
Reese
Thomas S
TS
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000378:metabolism*; D002478:Cells, Cultured; D006624:Hippocampus / Q000378:metabolism / Q000648:ultrastructure; D016253:Microscopy, Immunoelectron; D018377:Neurotransmitter Agents / Q000378:metabolism*; D010766:Phosphorylation; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D017729:Presynaptic Terminals / Q000378:metabolism* / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley; D016704:Synapsins / Q000378:metabolism*; D009435:Synaptic Transmission / Q000502:physiology*; D013572:Synaptic Vesicles / Q000378:metabolism* / Q000648:ultrastructure
D018377:Neurotransmitter Agents; D016704:Synapsins; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D011188:Potassium; D002118:Calcium