Ternary Kv4.2 channels recapitulate voltage‐dependent inactivation kinetics of A‐type K⁺ channels in cerebellar granule neurons

Abstract

Kv4 channels mediate most of the somatodendritic subthreshold operating A-type current (I SA ) in neurons. This current plays essential roles in the regulation of spike timing, repetitive firing, dendritic integration and plasticity. Neuronal Kv4 channels are thought to be ternary complexes of Kv4 pore-forming subunits and two types of accessory proteins, Kv channel interacting proteins (KChIPs) and the dipeptidyl-peptidase-like proteins (DPPLs) DPPX (DPP6) and DPP10. In heterologous cells, ternary Kv4 channels exhibit inactivation that slows down with increasing depolarization. Here, we compared the voltage dependence of the inactivation rate of channels expressed in heterologous mammalian cells by Kv4.2 proteins with that of channels containing Kv4.2 and KChIP1, Kv4.2 and DPPX-S, or Kv4.2, KChIP1 and DPPX-S, and found that the relation between inactivation rate and membrane potential is distinct for these four conditions. Moreover, recordings from native neurons showed that the inactivation kinetics of the I SA in cerebellar granule neurons has voltage dependence that is remarkably similar to that of ternary Kv4 channels containing KChIP1 and DPPX-S proteins in heterologous cells. The fact that this complex and unique behaviour (among A-type K + currents) is observed in both the native current and the current expressed in heterologous cells by the ternary complex containing Kv4, DPPX and KChIP proteins supports the hypothesis that somatically recorded native Kv4 channels in neurons include both types of accessory protein. Furthermore, quantitative global kinetic modelling showed that preferential closed-state inactivation and a weakly voltage-dependent opening step can explain the slowing of the inactivation rate with increasing depolarization. Therefore, it is likely that preferential closed-state inactivation is the physiological mechanism that regulates the activity of both ternary Kv4 channel complexes and native I SA -mediating channels. + channels containing Kv4 pore-forming subunits (Kv4 channels) mediate most of the subthreshold-operating somatodendritic transient or A-type K + current in neurons (also known as I SA ) (Serodio et al. 1994; reviewed in Jerng et al. 2004a). This current is fundamental to neuronal function. It can contribute to spike repolarization and has critical roles in the modulation of the frequency of repetitive firing, signal processing in dendrites and spike timing-dependent plasticity (Connor & Stevens, 1971; This paper has online supplemental material. Hoffman et al. 1997;Schoppa & Westbrook, 1999;Adams et al. 2000;Johnston et al. 2000Johnston et al. , 2003Hille, 2001;Liss et al. 2001;Ramakers & Storm, 2002;Kim et al. 2005Kim et al. , 2007Chen et al. 2006;Hu et al. 2006;Thompson, 2007). These functions rely on the precise voltage dependence and kinetic properties of the underlying K + channels. Studies in heterologous expression systems have shown that Kv4 channels may exist as ternary complexes composed of a pore-forming subunit and at least two distinct auxiliary subunits...

Multiple Kv Channel-interacting Proteins Contain an N-terminal Transmembrane Domain That Regulates Kv4 Channel Trafficking and Gating

“…In contrast, Kv4.2 inactivation accelerates with increasing voltage (8,25). This inverse voltage dependence appears to be characteristic of the Kv4 closed state inactivation mechanism, which becomes increasingly less effective with increasing depolarization (25)(26)(27). This result suggests that the primary effect of the KISD is to slow the kinetics of the closed state inactivation pathway, probably via slowed channel closing (7), after the KChIP core sequesters the N-type-like inactivation mechanism.…”

The Expression Pattern of a Cav3-Kv4 Complex Differentially Regulates Spike Output in Cerebellar Granule Cells

“…All chemicals were obtained from Sigma-Aldrich unless otherwise noted. Transverse cerebellar slices (250 -300 m) were prepared from the midline vermis region of male rats at postnatal days 19 -23 (P19 -P23) using established procedures (Anderson et al, 2010a). Briefly, animals were anesthetized with isoflurane until they were unresponsive to tail pinch, and the cerebellum was dissected out in artificial CSF (aCSF) composed of (in mM) 125 NaCl, 3.25 KCl, 1.5 CaCl 2 , 1.5 MgCl 2 , 25 NaHCO 3 , and 25 D-glucose preoxygenated by carbogen (95% O 2 , 5% CO 2 ) gas.…”

“…Kv4 channels are distinct among A-type channels in forming a complex with members of the calcium-sensing potassium channel interacting proteins (KChIPs; An et al, Jerng et al, 2005;Norris et al, 2010). An association of the Kv4 com-plex with Cav3 T-type calcium channels and KChIP3 was also shown to invoke a calcium-sensitive increase in I A that modifies spike output in cerebellar stellate cells (Molineux et al, 2005;Anderson et al, 2010aAnderson et al, , 2013. It is important, then, that both Cav3 calcium (Talley et al, 1999) and Kv4 potassium channel isoforms (Serô dio and Rudy, 1998;Amarillo et al, 2008) exhibit pronounced gradients of expression in granule cells over cerebellar lobules that could help define signal processing.…”

KV4.3 N-terminal deletion mutant D2-39

“…In addition to KChIPs, several additional β subunits may also be physiologically relevant modulators of K V 4 channels. 3,8 Such additional β subunits include dipeptidyl-aminopeptidase-like proteins (DPPX isoforms), [50][51][52][53][54][55] Min-K related peptides (MiRPs), [56][57][58][59][60] and K V β isoforms. 57,61,62 All of these " fit with τ = 108 ms; blue curve, truncated single exponential beginning at Δt = 60 ms with τ = 126 ms. Gray symbols and fits correspond to WT (solid circles) and Δ2-39 (hollow circles) obtained in the absence of KChIp2b (previously illustrated in Fig.…”

“…3,8,[50][51][52][53][54][55][56][57][58][59][60][61][62] However, for reasons to be addressed in Discussion, our coexpression studies focused exclusively on KChIP2b.…”