Regulation of NMDA receptor activity by F-actin and myosin light chain kinase.
The postsynaptic density (PSD) at excitatory dendritic synapses comprises a protein complex of glutamate receptors, scaffolding elements, and signaling enzymes. For example, NMDA receptors (NMDARs) are linked to several proteins in the PSD, such as PSD-95, and are also tethered via binding proteins such as alpha-actinin directly to filamentous actin of the cytoskeleton. Depolymerization of the cytoskeleton modulates the activity of NMDARs, and, in turn, strong activation of NMDARs can trigger depolymerization of actin. Myosin, the motor protein of muscular contraction and nonmuscle motility, is also associated with NMDARs and the PSD. We show here that constitutively active myosin light chain kinase (MLCK) enhances NMDAR-mediated whole-cell and synaptic currents in acutely isolated CA1 pyramidal and cultured hippocampal neurons, whereas inhibitors of MLCK depress these currents. This MLCK-dependent regulation was observed in cell-attached patches but was lost after excision to inside-out patches. Furthermore, the enhancement induced by constitutively active MLCK and the depression of MLCK inhibitors were eliminated after depolymerization of the cytoskeleton. NMDARs and MLCK did not colocalize in clusters on the dendrites of cultured hippocampal neurons, further indicating that the effects of MLCK are mediated indirectly via actomyosin. Our results suggest that MLCK enhances actomyosin contractility to either increase the membrane tension on NMDARs or to alter physical relationships between the actin cytoskeleton and the linker proteins of NMDARs.
Lei
S
S
Canadian Institutes of Health Research Group "The Synapse," Departments of Physiology and Pharmacology, University of Toronto, Toronto M5S 1A8, Canada.
Czerwinska
E
E
Czerwinski
W
W
Walsh
M P
MP
MacDonald
J F
JF
D000199:Actins / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002232:Carbocyanines; D002469:Cell Separation; D002478:Cells, Cultured; D003712:Dendrites / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D005456:Fluorescent Dyes; D006624:Hippocampus; D051379:Mice; D009219:Myosin-Light-Chain Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000494:pharmacology; D016202:N-Methylaspartate / Q000494:pharmacology; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D017966:Pyramidal Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects / Q000378:metabolism*
D000199:Actins; D002232:Carbocyanines; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; C409466:NR1 NMDA receptor; D016194:Receptors, N-Methyl-D-Aspartate; C089187:cyanine dye 3; D016202:N-Methylaspartate; D009219:Myosin-Light-Chain Kinase; D002118:Calcium