Calcium-dependent maintenance of agrin-induced postsynaptic specializations.
Although much progress has been made in understanding synapse formation, little is known about the mechanisms underlying synaptic maintenance and loss. The formation of agrin-induced AChR clusters on cultured myotubes requires both activation of the receptor tyrosine kinase MuSK and intracellular calcium fluxes. Here, we provide evidence that such AChR clusters are maintained by agrin/MuSK-induced intracellular calcium fluxes. Clamping intracellular calcium fluxes after AChR clusters have formed leads to rapid MuSK and AChR tyrosine dephosphorylation and cluster dispersal, even in the continued presence of agrin. Both the dephosphorylation and the dispersal are inhibited by the tyrosine phosphatase inhibitor pervanadate. In contrast, clamping intracellular calcium at the time of initial agrin stimulation has no effect on agrin-induced MuSK or AChR phosphorylation, but blocks AChR cluster formation. These findings suggest an avenue by which postsynaptic stability can be regulated by modification of intracellular signaling pathways that are distinct from those used during synapse formation.
Megeath
L J
LJ
Department of Neuroscience, Brown University, Box 1953, 190 Thayer Street, Providence, RI 02912, USA.
Kirber
M T
MT
Hopf
C
C
Hoch
W
W
Fallon
J R
JR
D000109:Acetylcholine / Q000494:pharmacology; D018171:Agrin / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D002038:Bungarotoxins / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D002642:Chick Embryo; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005110:Extracellular Space / Q000378:metabolism; D016257:Fura-2 / Q000378:metabolism; D042541:Intracellular Space / Q000378:metabolism; D018485:Muscle Fibers, Skeletal; D010766:Phosphorylation; D011485:Protein Binding; D051381:Rats; D011940:Receptor Aggregation / Q000187:drug effects*; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D011950:Receptors, Cholinergic / Q000187:drug effects / Q000378:metabolism*; D013569:Synapses / Q000187:drug effects; D013997:Time Factors; D014638:Vanadates / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology
D018171:Agrin; D002038:Bungarotoxins; D002614:Chelating Agents; D004791:Enzyme Inhibitors; D011950:Receptors, Cholinergic; D014665:Vasodilator Agents; C076715:pervanadate; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D014638:Vanadates; D004533:Egtazic Acid; D020794:Receptor Protein-Tyrosine Kinases; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D000109:Acetylcholine; D002118:Calcium; D016257:Fura-2