Dipeptidyl‐peptidase‐like‐proteins confer high sensitivity to the scorpion toxin AmmTX3 to Kv4‐mediated A‐type K⁺ channels

Abstract

Key points• AmmTX3, a member of the α-KTX15 family of scorpion toxins, efficiently and specifically blocks the subthreshold-operating A-type K + current in cerebellar granule neurons from wild-type mice but not in neurons from mice lacking the Kv4 channel-associated protein DPP6.• In heterologous cells high-affinity blockade of Kv4.2 and Kv4.3 channels by AmmTX3 requires the presence of the associated proteins DPP6 and DPP10.• These results validate AmmTX3 as a specific blocker of Kv4 channels in CNS neurons and explain the discrepancy between previous observations in neurons and heterologous cells.• They contribute a powerful tool to investigate the physiological role of A-type K + currents, believed to be important in dendritic integration and plasticity and to be involved in a number of diseases.• Our results demonstrate that, in addition to changing the kinetics and voltage dependence of Kv4 channel complexes, DDP-like Kv4-associated proteins also affect their pharmacological profile.Abstract K + channels containing Kv4.2 and Kv4.3 pore-forming subunits mediate most of the subthreshold-operating somatodendritic A-type K + current in CNS neurons. These channels are believed to be important in regulating the frequency of repetitive firing, the backpropagation of action potential into dendrites, and dendritic integration and plasticity. Moreover, they have been implicated in several diseases from pain to epilepsy and autism spectrum disorders. The lack of toxins that specifically and efficiently block these channels has hampered studies aimed at confirming their functional role and their involvement in disease. AmmTX3 and other related members of the α-KTX15 family of scorpion toxins have been shown to block the A-type K + current in cultured neurons, but their specificity has been questioned because the toxins do not efficiently block the currents mediated by Kv4.2 or Kv4.3 subunits expressed in heterologous cells. Here we show that the high-affinity blockade of Kv4.2 and Kv4.3 channels by AmmTX3 depends on the presence of the auxiliary subunits DPP6 and DPP10. These proteins are thought to be components of the Kv4 channel complex in neurons and to be important for channel expression in dendrites. These studies validate the use of AmmTX3 as a blocker of the Kv4-mediated A-type K + current in neurons.

Roles of specific Kv channel types in repolarization of the action potential in genetically identified subclasses of pyramidal neurons in mouse neocortex

“…Rudy and colleagues showed that this agent is highly selective for channels containing K v 4 ␣-subunits in association with DPP6 or DPP10 auxiliary subunits (Maffie et al 2013). We found that unlike 4-AP and BaCl 2 AmmTx3 had no effects on RMP [etv1 (10 cells AmmTx3 application resulted in significant AP broadening (HW and width at threshold) and significant reduction of dV/dt for repolarization in all pyramidal cell subtypes tested, with no changes in voltage threshold (Fig.…”

“…We found that the recently characterized peptide blocker AmmTx3 (200 nM; Maffie et al 2013) was selective for the peak transient A-type current over the steady-state current (and did not affect input resistance or RMP) in neocortical pyramidal cells. These voltage-clamp data with AmmTx3 also indicate that dipeptidyl peptidase-like-proteins (DPP6 or DPP10) Data are means Ϯ SE for 11 (layer 2/3), 10 (etv1), and 10 (glt) cells.…”

“…These include DTX (at 100 nM) for K v 1 channels (channels containing K v 1.1, K v 1.2, or K v 1.6 subunits; Harvey and Robertson 2004), GxTx (at 100 nM) for K v 2 channels (Herrington et al 2006;Liu and Bean 2014), and the peptide AmmTx3, a highly selective blocker of K v 4 channels in association with dipeptidyl peptidase-like (DPP) proteins (Maffie et al 2013). We also tested the commonly used putative A-type current blockers, 4 mM 4-AP and 150 M BaCl 2 .…”

“…A: representative traces for single APs in a layer 2/3 pyramidal neuron before and after application of 200 nM AmmTx3 (blocks K v 4 channels associated with DPP6 or DPP10 subunits;Maffie et al 2013). Inset: same APs at longer time base.…”

Chromatin-bound RNA and the neurobiology of psychiatric disease

“…One interesting case in point is the 744bp long ncRNA, LOC389023 , positioned in chromosome 2q14.1, within the gene body of DPP10 . The DPP10 gene encodes a dipeptidyl peptidase-related protein regulating voltage-dependent potassium channels that control neuronal excitability, membrane repolarization and repetitive firing, back propagation of action potential into dendrites, and dendritic integration and plasticity (Jerng et al, 2005, Zagha et al, 2005, Li et al, 2006, Maffie and Rudy, 2008, Maffie et al, 2013). Interestingly, rare structural variants of DPP10 confer strong genetic susceptibility to autism (Girirajan et al, 2013) and asthma (Torgerson et al, 2012), while some of the gene’s more common variants contribute to a significant risk for bipolar disorder, schizophrenia and asthma (Allen et al, 2003, Marshall et al, 2008, Djurovic et al, 2010, Michel et al, 2010).…”