Myelin supports rapid neuronal signalling by siphoning potassium (K⁺) away from axons following action potentials, a process mediated by inward-rectifier potassium channels (K_ir channels). In Multiple Sclerosis (MS), demyelination disrupts this mechanism. However, the precise alterations in myelin function and their consequences for neuronal activity remain poorly understood. Patch clamp recordings indicate that elevated extracellular [K⁺] can activate transient receptor potential ankyrin 1 (TRPA1) in oligodendrocytes, whose activation then leads to inhibition of K_ir channels (Hamilton et al., 2016). This may impair K⁺ clearance and promote neuronal hyperexcitability. Such changes could contribute to epileptogenesis, but the functional relationship between TRPA1 and K_ir channels remains unclear.

Here, we investigated the role of TRPA1 in K⁺ siphoning and neuronal activity using compound action potential (CAP) recordings from optic nerves of wild-type (WT) C57Bl/6J mice and oligodendrocyte-specific TRPA1 conditional knockout mice (Sox10 iCreER^T2:TRPA1^fl/fl; cKO). High-frequency stimulation (HFS; 100Hz) was applied to mimic seizure-like activity and induce partial conduction block via elevated periaxonal K⁺, and recovery rates were quantified as a measure of K⁺ siphoning capacity (Larson et al., 2018).

In WT optic nerves, application of the K_ir channel antagonist BaCl₂ (100µM) significantly prolonged recovery following 30 s HFS (Control: n=8, mean ± SEM: 76.6 ± 15.9s; BaCl₂: n=10, 276.5 ± 25.7s; Student’s t-test, P<0.0001). Similarly, activation of TRPA1 with the agonist polygodial (100 µM) impaired recovery (Control: n=10, 51.6 ± 6.0s; polygodial: n=6, 81.2 ± 13.9s; Student’s t-test, P=0.041), consistent with reduced K⁺ siphoning. Interestingly, polygodial application further exacerbated recovery impairment in cKO nerves following 300s HFS compared with WT nerves (WT: n=7, 270.9 ± 30.3s; cKO: n=9, 392.9 ± 19.8s; Student’s t-test, P=0.0043). These results indicate that TRPA1 knockout in oligodendrocytes is not therapeutic and indeed reduces their capacity for potassium syphoning. In line with this, we find that TRPA1 knockout leads to a reduction in potassium channel function and expression in oligodendrocytes.

To assess whether oligodendrocyte TRPA1 deletion alters seizure susceptibility, epilepsy was induced in cKO mice and WT littermates using pentylenetetrazole (PTZ), and the latency to Racine scale stages was measured. In parallel, we have ongoing experiments using electrocorticography (ECoG) recordings from the motor and somatosensory cortex, to evaluate alterations in brain activity and circadian rhythms.

We found that a higher proportion of cKO mice reached Racine stage 4 (loss of posture) and stage 5 (tonic–clonic seizures) after injection of PTZ. Latency to stage 4 was reduced in cKO mice (WT: n=4, 794.3 ± 185.8s; cKO: n=9, 315.4 ± 41.1s; Student’s t-test, P=0.0041), as was latency to stage 5 (WT: n=4, 891.0 ± 178.2s; cKO: n=6, 385.3 ± 81.1s; Student’s t-test, P=0.0195).

Preliminary ECoG recordings revealed brief spike events in the motor cortex, but not the somatosensory cortex of cKO mice (WT: n=1/11; cKO: n=6/14; Fisher’s exact test, P=0.09), suggesting increased vulnerability of motor cortical circuits following oligodendrocyte-specific TRPA1 deletion.

In summary, TRPA1 regulates K_ir channel-mediated K⁺ siphoning and neuronal excitability. Both pharmacological activation and genetic deletion of oligodendrocyte TRPA1 impair K⁺ clearance, potentially disrupting neuronal stability and increasing seizure susceptibility.