TRPA1-Dependent Regulation of Oligodendrocyte Potassium Channels Affects Myelin Function and Seizure Susceptibility
Oligodendrocytes (OLs) help maintain central nervous system homeostasis by siphoning extracellular potassium (K⁺) from the periaxonal space after neuronal activity, a process mediated primarily by inwardly rectifying K⁺ channels (Kir). Disruption of this mechanism slows axonal conduction and promotes neuronal hyperexcitability and seizures, common in demyelinating conditions. Prior work suggests the transient receptor potential ankyrin 1 channel (TRPA1), expressed by mature OLs, modulates K⁺ channel function (Hamilton et al., 2016), but how TRPA1 interacts with distinct K⁺ channel populations remains unclear. We combined whole‑cell patch‑clamp recordings from grey matter (GM) and white matter (WM) OLs with compound action potential (CAP) recordings and behavioural assays in TRPA1‑knockout mice to define how TRPA1 regulates K⁺ conductance (gK), myelin function, and seizure vulnerability.
Patch‑clamp recordings revealed region‑specific regulation of K⁺ channels. Blocking Kir channels with barium (100 µM) reduced gK in GM OLs but had minimal effects in WM OLs (GM: ΔgK (%) = −30.7±4.2, n=11; WM: ΔgK (%) = −3.2±3.0, n = 29, P<0.0001). Activation of TRPA1 with multiple agonists inhibited gK; in WM OLs, the TRPA1‑mediated ΔgK evoked by carvacrol was −42.43 ± 2.66 % (n=55). This inhibition was attenuated by pre‑incubation with both Kir and K2P channel antagonists (ΔgK = −24.2±4.5%, n=7, P=0.03), but not by blocking Kir alone (ΔgK = −66.7±6.44%, n=17, P<0.0001) or K2P alone (ΔgK = −38.1±10.8 %, n=6, P=0.82), indicating that TRPA1 regulates both channel types and engages bidirectional compensation in WM.
To evaluate K⁺ siphoning, we recorded CAPs from optic nerves of wild‑type (WT) and OL‑specific TRPA1 conditional‑knockout (Sox10-iCreERT2:TRPA1flfl; cKO) mice. High‑frequency stimulation (HFS, 100 Hz) induces periaxonal K⁺ accumulation, and the recovery from conduction block approximates the rate of K⁺ siphoning (Larson et al., 2018). In WT nerves, TRPA1 activation with polygodial (100 µM) slowed recovery (Control: 51.6±6.0 s, n=10; polygodial: 81.2±13.9 s, n=6; P=0.041). Surprisingly, after prolonged HFS (300s), cKO nerves incubated with polygodial recovered even more slowly than WT (WT: 270.9±30.3 s, n=7; cKO: 392.9±19.8 s, n=9; P=0.0043), indicating that TRPA1 loss is not protective and may impair developmental tuning of K⁺ channel function or expression.
Preliminary immunohistochemistry supports this: TRPA1 global knockout mice show reduced GIRK1 expression at P14 (P = 0.09, nwt=5, nko=5), increased Kir4.1 at P30 (P=0.008, nwt=5, nko=5), and a transient reduction in MBP at P21 (P=0.01, nwt=5, nko=5), accompanied by reduced gK at P12–18, which recovers by P25-30.
Behaviourally, adult cKO mice exhibit heightened pentylenetetrazole seizure susceptibility. Latency to Racine stage 4 (loss of posture) decreased from 794.3±185.8 s (n=4) in WT to 315.4±41.1 s (n=9) in cKO (P=0.004). Latency to stage 5 (tonic-clonic) decreased from 891.0±178.2 s (n=4) to 385.3±81.1 s (n=6, P=0.02). Preliminary electrocorticography showed increased spike events (>0.6/hr) in motor cortex, but none in somatosensory cortex, of cKO mice (WT: n=1/11; cKO: n=6/14; P=0.08), suggesting circuit‑specific vulnerability.
Together, these data identify TRPA1 as a key regulator of oligodendroglial K⁺ channel function, reveal region‑specific compensatory mechanisms across Kir and K2P channels, and show that perturbing TRPA1 compromises myelin function, slows axonal recovery after activity, and increases seizure propensity.
