The long-term objectives are to understand how voltage-gated potassium (Kv) channels are localized into the proper subcellular compartments and how their localization affects neuronal excitability, and thus to develop new strategies for treating neurological diseases. Kv channel dysfunction causes diseases of brain, heart and muscle. Kv channels are the primary targets of pharmaceutical interventions to treat epilepsies, arrhythmias, neuropathic pain, and multiple sclerosis. Due to broad channel expression in many cell types, blockers or activators often bring severe side effects. Recent studies show that each Kv channel displays a distinct pattern of polarized targeting in neurons. It is the emerging theme that such polarized targeting affects neuronal excitability. However, the exact mechanism and function of Kv channel targeting remain mystery. Kv3 (Shaw) channels are unique among Kv channels in their high activation threshold and rapid deactivation kinetics. They are required for rapid spiking and involved in dendritic integration and transmitter release. Human adult-onset ataxia caused by mutations in Kv3.3 gene is a testament for their important functions. Reflecting their diverse functions, Kv3 channels display complex targeting patterns that are governed by unknown mechanisms. Our preliminary studies show that the two splice variants of Kv3.1 have identical channel properties but differentially regulate action potential firing. Interestingly, they differ in axon-dendrite targeting. Based on our preliminary data, we propose a new model that action potential firing is regulated by Kv3 channel targeting, which is in turn regulated by alternative splicing and protein phosphorylation. We will test three hypotheses in this model with three aims. By taking a multidisciplinary approach that includes electrophysiology, imaging, molecular biology and protein biochemistry techniques, we will determine whether:
(Aim 1) polarized targeting of Kv channels is critical for action potential firing;
(Aim 2) ankyrin G at the axon initial segment functions as a conditional barrier for Kv3 splice variants;
(Aim 3) protein phosphorylation regulates Kv3 channel targeting and hence action potential firing. Our research will contribute to generate a new therapeutic strategy and reveal new drug targets for specifically controlling Kv3 channel functions in neurons, e.g. developing small peptides and kinase inhibitors as the treatment of ataxia, epilepsy and sleeping disorders.
Kv channels are the primary targets of pharmaceutical interventions to treat many diseases, in which the specificity of channel modulation is the key. Recent studies show that each Kv channel has its characteristic distribution pattern in nerve cells. Therefore, our project to understand how Kv channels are localized to regulate functions of nerve cells will contribute to generate novel strategies for treating diseases of the nervous systems.
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