{'fraction_non_alphanumeric': 0.02952029520295203, 'fraction_numerical': 0.01783517835178352, 'mean_word_length': 5.779166666666667, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Frequency-Dependent Inactivation of Mammalian A-Type K+ Channel KV1.4 Regulated by Ca2+/Calmodulin-Dependent Protein Kinase

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.