Cellular and Subcellular Localisation of Kv4-Associated KChIP Proteins in the Rat Cerebellum

Abstract

The K+ channel interacting proteins (KChIPs) are a family of cytosolic proteins that interact with Kv4 channels, leading to higher current density, modulation of channel inactivation and faster recovery from inactivation. Using immunohistochemical techniques at the light and electron microscopic level combined with quantitative analysis, we investigated the cellular and subcellular localisation of KChIP3 and KChIP4 to compare their distribution patterns with those for Kv4.2 and Kv4.3 in the cerebellar cortex. Immunohistochemistry at the light microscopic level demonstrated that KChIP3, KChIP4, Kv4.2 and Kv4.3 proteins were widely expressed in the cerebellum, with mostly overlapping patterns. Immunoelectron microscopic techniques showed that KChIP3, KChIP4, Kv4.2 and Kv4.3 shared virtually the same somato-dendritic domains of Purkinje cells and granule cells. Application of quantitative approaches showed that KChIP3 and KChIP4 were mainly membrane-associated, but also present at cytoplasmic sites close to the plasma membrane, in dendritic spines and shafts of Purkinje cells (PCs) and dendrites of granule cells (GCs). Similarly, immunoparticles for Kv4.2 and Kv4.3 were observed along the plasma membrane and at intracellular sites in the same neuron populations. In addition to the preferential postsynaptic distribution, KChIPs and Kv4 were also distributed presynaptically in parallel fibres and mossy fibres. Immunoparticles for KChIP3, KChIP4 and Kv4.3 were detected in parallel fibres, and KChIP3, KChIP4, Kv4.2 and Kv4.3 were found in parallel fibres, indicating that composition of KChIP and Kv4 seems to be input-dependent. Together, our findings unravelled previously uncharacterised KChIP and Kv4 subcellular localisation patterns in neurons, revealed that KChIP have additional Kv4-unrelated functions in the cerebellum and support the formation of macromolecular complexes between KChIP3 and KChIP4 with heterotetrameric Kv4.2/Kv4.3 channels.

Pharmacological Approaches for the Modulation of the Potassium Channel KV4.x and KChIPs

“…The location, expression, or morphological changes of the KChIPs in different tissues, such as the brain [ 28 ] or the heart [ 33 ], open new opportunities for the treatment of diseases related to these systems. For example, KChIP2 (at the RNA level) is downregulated in several cardiac pathologies (atrial fibrillation, cardiac hypertrophy, or heart failure) [ 18 , 40 , 75 ].…”

“…Moreover, it has been described that K V 4.3 and Na V 1.5 influence the function of each other [ 24 , 25 ]; the existence of a channelosome formed by K V 4.3, KChIP3, and Ca V 3.1 channels has also been described [ 26 , 27 ]. The expression of β subunits varies both among organs and/or among different regions of the same organ [ 3 , 12 , 28 , 29 , 30 , 31 , 32 , 33 ]. Therefore, the function of these channels depends not only on the tissue where they are expressed, but also on the signaling context, involving accessory subunits, kinases, or even other ion channels.…”

Human outperform mouse Purkinje cells in dendritic complexity and computational capacity

“…The neck C m was set to 3μF/cm 2 instead, the head CM was set to 1μF/cm 2 . The ionic channels were placed only on the spine heads: Cav2.1 (P-type), Kca1.1 (BK) Kca2.2 (SK2) 60,71 , Kv4.3 (A-type), Cav3.1 (T-type) 72,73 . The calcium channel Cav2.3 was experimentally proven not to be critical for intrinsic and synaptic responses, so it was omitted 72 .…”

The Role of Vti1a in Biological Functions and Its Possible Role in Nervous System Disorders

“…The K channel interacting proteins (KChIPs) belong to the neuronal calcium receptor family and assemble into a natural complex with the α subunit of the voltage-gated Kv4 potassium channel, encoding A-type K + current to regulate neuronal excitability ( Bähring, 2018 ; Kise et al, 2021 ). The specific assembly contributes to forming and stabilizing voltage-gated potassium channel tetramers and increases channel transport to the cell membrane surface ( Alfaro-Ruíz et al, 2020 ). For example, siRNA-mediated knockdown of Vti1a or VAMP7 inhibited Kv4/KChIP1 transport to the Neuro2A cell membrane ( Flowerdew and Burgoyne, 2009 ).…”