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Frequency-dependent inactivation of mammalian A-type K+ channel KV1.4 regulated by Ca2+/calmodulin-dependent protein
1Zentrum für Molekulare Neurobiologie, Martinistrasse 52, D-20246 Hamburg, Germany.
Abstract:
Ca2+/calmodulin dependent protein kinase (CaMKII) and protein phosphatase 2B (calcineurin) are key enzymes in the regulation of synaptic strength, controlling the phosphorylation status of pre- and postsynaptic target proteins. Here, we show that the inactivation gating of the Shaker-related fast-inactivating KV channel, Kv1.4 is controlled by CaMKII and the calcineurin/inhibitor-1 protein phosphatase cascade. CaMKII phosphorylation of an amino-terminal residue of KV1.4 leads to slowing of inactivation gating and accelerated recovery from N-type inactivated states. In contrast, dephosphorylation of this residue induces a fast inactivating mode of KV1.4 with time constants of inactivation 5 to 10 times faster compared with the CaMKII-phosphorylated form. Dephosphorylated KV1.4 channels also display slowed and partial recovery from inactivation with increased trapping of KV1.4 channels in long-absorbing C-type inactivated states. In consequence, dephosphorylated KV1.4 displays a markedly increased tendency to undergo cumulative inactivation during repetitive stimulation. The balance between phosphorylated and dephosphorylated KV1.4 channels is regulated by changes in intracellular Ca2+ concentration rendering KV1.4 inactivation gating Ca2+-sensitive. The reciprocal CaMKII and calcineurin regulation of cumulative inactivation of presynaptic KV1.4 may provide a novel mechanism to regulate the critical frequency for presynaptic spike broadening and induction of synaptic plasticity.
Insights
Ca2+/calmodulin dependent protein kinase (CaMKII) and calcineurin regulate Kv1.4 channel inactivation. CaMKII phosphorylation slows inactivation, while dephosphorylation accelerates it, impacting synaptic plasticity.
Area of Science:
- Neuroscience
- Molecular Biology
- Ion Channel Physiology
Background:
- Synaptic strength is modulated by protein phosphorylation, involving key enzymes like CaMKII and calcineurin.
- Kv1.4 channels, crucial for neuronal excitability, exhibit fast inactivation gating.
Purpose of the Study:
- To investigate the regulatory mechanisms controlling Kv1.4 channel inactivation gating.
- To determine the roles of CaMKII and calcineurin in modulating Kv1.4 channel function.
Main Methods:
- Electrophysiological recordings of Kv1.4 channel currents.
- Biochemical assays to assess protein phosphorylation status.
- Site-directed mutagenesis to identify key phosphorylation sites.
Main Results:
- CaMKII phosphorylation of a Kv1.4 amino-terminal residue slows inactivation and speeds recovery.
- Dephosphorylation by calcineurin/inhibitor-1 accelerates inactivation and slows recovery, promoting cumulative inactivation.
- Kv1.4 inactivation gating is sensitive to intracellular Ca2+ concentration.
Conclusions:
- CaMKII and calcineurin reciprocally regulate Kv1.4 channel inactivation gating.
- This regulation provides a novel mechanism for controlling presynaptic spike broadening and synaptic plasticity induction.