Investigation of the role of axonal voltage-gated potassium channels in Direct Current Stimulation

Abstract

(from The role of axonal voltage-gated potassium channels in tDCS, Vasu and Kaphzan, 2022)

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Background: Transcranial direct current stimulation (tDCS) is a non-invasive sub-threshold stimulation, widely accepted for its amelioration of distinct neuropsychiatric disorders. The weak electric field of tDCS modulates the activity of cortical neurons, which in turn modifies brain functioning. However, the underlying mechanisms for that are not fully understood.

Objective/Hypothesis: Previous studies demonstrated that the axons are the most sensitive subcellular compartment for tDCS-induced polarization. Moreover, it was posited that DCS-induced axonal polarization is amplified by modifying the conductance of ionic channels. We posit that voltage-gated potassium-channels that are highly expressed in axons play a crucial role in DCS-induced modulation of cortical neurons functioning.

Methods: We examined the involvement of voltage-gated potassium-channels in the active modulation of spontaneous vesicle release by DCS. For that, we measured spontaneous excitatory postsynaptic currents (sEPSCs) from layer-V motor cortex during DCS application, while co-applying distinct voltage-gated potassium-channels blockers. Moreover, we examined the role of Kv1 potassium channels in DCS-induced modulation of action potential waveform at axon terminals by recording action potentials at terminal axon blebs during DCS application while locally inhibiting the Kv1 potassium-channels.

Results: We demonstrated that inhibiting voltage-gated potassium-channels occluded the DCS-induced modulation of subthreshold presynaptic vesicle release. Moreover, we showed that inhibiting Kv1 voltage-gated potassium-channels also occluded the DCS-induced modulation of action potential waveform at axon terminals.

Conclusion: We suggest that DCS-induced depolarization inactivates the Kv1 potassium channels thus reducing potassium conductance, which amplifies axonal depolarization, subsequently enhancing the presynaptic component of synaptic transmission. Whereas DCS-induced hyperpolarization induces opposite effects.

Method

Slices production for electrophysiology

Slices were produced by cutting with a Campden vibratome 7000smz-2 that has a Zero Z technology to minimize Z-axis deflection. Animals were cervically dislocated and its brain is taken immediately to harvest cortical coronal slices (300 μm) using Campden Vibratome 7000 smz2 (Campden Instruments, UK) in the fluff of frozen slicing solution (in mM): 110 Sucrose, 60 NaCl, 3 KCl, 1.25 NaH2PO4, 28 NaHCO3, 0.5 CaCl2, 7 MgCl2, 5 Glucose. Slices were kept for incubation at 34.5 °C for ∼1.5 h in artificial cerebrospinal fluid (ACSF) containing in mM: 125 NaCl, 2.5 KCl, 1.25 NaH2PO4, 25 NaHCO3, 25 d-glucose, 2 CaCl2, and 1 MgCl2. An additional recovery period of 30 min at room temperature was given inside the electrophysiology chamber in ACSF (2 mL/min).