KCNH4

KCNH4 (Kv12.3) encodes a low-threshold voltage-gated potassium channel of the Elk subfamily within the EAG superfamily (PMID:12890647, PMID:23712551). It assembles into functional channels and forms selective heteromultimers with other Elk family members (KCNH8 and KCNH3) but cannot co-assemble with Eag, Erg, or Kv family subunits, defining a restricted subfamily-specific oligomerization rule (PMID:12890647). Channel gating is modulated by extracellular pH: external acidification depolarizes the conductance-voltage relationship and suppresses low-threshold activation, an effect mediated by EAG-specific acidic residues in the voltage sensor that also confer divalent cation (Zn2+/Mg2+) sensitivity (PMID:23712551). Beyond its biophysical characterization, the corpus links KCNH4 expression to neuronal contexts but does not establish a mechanism downstream of the channel. No structural model, no native heteromeric complex composition in tissue, and no disease-causing mutation have been characterized in the available corpus.

1. 2003 Medium

   Established the subunit assembly rules for KCNH4, answering whether it forms homomeric channels or combines with other channel families.

   Evidence Coexpression of dominant-negative KCNH4 with other channel subunits in Xenopus oocytes with electrophysiological readout

   PMID:12890647

   Open questions at the time

   • Native heteromeric stoichiometry in neurons not determined
   • Whether endogenous KCNH4/KCNH8 heteromers occur in tissue untested
   • No structural basis for subfamily-restricted assembly
2. 2013 Medium

   Defined the molecular determinant of proton modulation, showing how extracellular pH tunes KCNH4 voltage-sensor activation.

   Evidence Conductance-voltage recordings plus site-directed mutagenesis of voltage-sensor acidic residues across EAG superfamily members including Kv12.3

   PMID:23712551

   Open questions at the time

   • Physiological pH range over which modulation is relevant in vivo not established
   • Functional consequence of pH gating in native neurons untested
   • No structural model of the protonated voltage sensor
3. 2021 Low

   Placed KCNH4 protein in pH-sensitive central chemoreceptor neurons, connecting its proton sensitivity to a candidate physiological setting.

   Evidence Immunofluorescence, Western blot, and qPCR in Phox2b-expressing NTS neurons of mouse brainstem

   PMID:33903883

   Open questions at the time

   • Localization only; no functional role for KCNH4 in chemoreception demonstrated
   • No loss-of-function or knockout phenotype
   • Co-localization with Phox2b does not establish channel contribution to neuronal firing
4. 2015 Low

   Linked KCNH4 transcript abundance to tau levels, raising the channel as a downstream node of tau-associated changes in neuronal excitability and proliferation.

   Evidence Tau plasmid transfection in mouse N2A and human SK-N-SH neuroblastoma cells with qRT-PCR, patch-clamp, and proliferation assays

   PMID:25590133 PMID:26576773

   Open questions at the time

   • mRNA-level effect only; no direct link to KCNH4 protein or to the channel as the proliferation driver
   • KCNH4 is one of several Kv channels affected, so specificity is unresolved
   • Mechanism connecting tau to KCNH4 transcription unknown
5. 2020 Low

   Extended transcriptional regulation of KCNH4 to a second perturbation, CLN1/PPT1 overexpression, again reducing Kv12 channel function.

   Evidence RNA-seq and patch-clamp with pharmacological dissection (4-AP, NS-1643) in CLN1-overexpressing SH-SY5Y cells

   PMID:33390903

   Open questions at the time

   • Kv12 reduction inferred pharmacologically; KCNH4 not directly manipulated
   • Direct versus indirect transcriptional effect not distinguished
   • No demonstration that KCNH4 loss accounts for the cellular phenotype

• The native channel composition, in vivo physiological function, and any disease relevance of KCNH4 remain unresolved.
• No structural model of the channel or its voltage sensor
• No loss-of-function phenotype establishing a neuronal or systemic role
• No characterized causative disease mutation