ABSTRACT
Voltage-dependent Kv2.1 K(+) channels, which mediate delayed rectifier Kv currents (I(K)), are expressed in large clusters on the somata and dendrites of principal pyramidal neurons, where they regulate neuronal excitability. Here we report activity-dependent changes in the localization and biophysical properties of Kv2.1. In the kainate model of continuous seizures in rat, we find a loss of Kv2.1 clustering in pyramidal neurons in vivo. Biochemical analysis of Kv2.1 in the brains of these rats shows a marked dephosphorylation of Kv2.1. In cultured rat hippocampal pyramidal neurons, glutamate stimulation rapidly causes dephosphorylation of Kv2.1, translocation of Kv2.1 from clusters to a more uniform localization, and a shift in the voltage-dependent activation of I(K). An influx of Ca(2+) leading to calcineurin activation is both necessary and sufficient for these effects. Our finding that neuronal activity modifies the phosphorylation state, localization and function of Kv2.1 suggests an important link between excitatory neurotransmission and the intrinsic excitability of pyramidal neurons.
Subject(s)
Glutamic Acid/pharmacology , Ion Channel Gating/drug effects , Neuronal Plasticity/physiology , Potassium Channels, Voltage-Gated , Potassium Channels/metabolism , Pyramidal Cells/metabolism , Animals , Animals, Newborn , Blotting, Western , Cadmium Chloride/pharmacology , Calcimycin/pharmacology , Calcium Channel Blockers/pharmacology , Cell Count , Cells, Cultured , Cyclosporine/pharmacology , Delayed Rectifier Potassium Channels , Dendrites/drug effects , Dendrites/physiology , Disease Models, Animal , Dose-Response Relationship, Drug , Drug Interactions , Enzyme Inhibitors/pharmacology , Excitatory Amino Acid Antagonists/pharmacology , Hippocampus/cytology , Ionophores/pharmacology , Kainic Acid/pharmacology , Membrane Potentials/drug effects , Membrane Potentials/physiology , Neuronal Plasticity/drug effects , Nitrendipine/pharmacology , Nitriles , Okadaic Acid/pharmacology , Patch-Clamp Techniques/methods , Phosphoprotein Phosphatases/pharmacology , Phosphorylation/drug effects , Potassium/metabolism , Potassium Channel Blockers/pharmacology , Potassium Chloride/pharmacology , Pyramidal Cells/drug effects , Pyrethrins/pharmacology , Rats , Seizures/chemically induced , Seizures/physiopathology , Shab Potassium Channels , Time Factors , Translocation, Genetic/drug effects , Translocation, Genetic/physiologyABSTRACT
Voltage-dependent potassium channels regulate membrane excitability and cell-cell communication in the mammalian nervous system, and are found highly localized at distinct neuronal subcellular sites. Kv1 (mammalian Shaker family) potassium channels and the neurexin Caspr2, both of which contain COOH-terminal PDZ domain binding peptide motifs, are found colocalized at high density at juxtaparanodes flanking nodes of Ranvier of myelinated axons. The PDZ domain-containing protein PSD-95, which clusters Kv1 potassium channels in heterologous cells, has been proposed to play a major role in potassium channel clustering in mammalian neurons. Here, we show that PSD-95 colocalizes precisely with Kv1 potassium channels and Caspr2 at juxtaparanodes, and that a macromolecular complex of Kv1 channels and PSD-95 can be immunopurified from mammalian brain and spinal cord. Surprisingly, we find that the high density clustering of Kv1 channels and Caspr2 at juxtaparanodes is normal in a mutant mouse lacking juxtaparanodal PSD-95, and that the indirect interaction between Kv1 channels and Caspr2 is maintained in these mutant mice. These data suggest that the primary function of PSD-95 at juxtaparanodes lies outside of its accepted role in mediating the high density clustering of Kv1 potassium channels at these sites.
