TTX ‐S/ TTX ‐R Na ⁺ Currents Coordinately Fine‐Tune Depolarization/Firing Capability Revealed by Voltage Derivatives/Displacement Current Phase Plots With Dynamic Current‐Clamp Simulation in Rat Visceral Sensory Neurons

AIM: channels coordinately fine-tune action potential (AP) depolarization and firing capability in rat nodose visceral sensory neurons. METHODS: APs were recorded by ruptured-patch current clamp in unmyelinated C-type and myelinated Ah-type neurons from isolated and sliced nodose ganglia. Voltage derivatives and displacement current phase plots were used to determine the kick-in voltage of TTX-R following TTX-S activation. Myelinated A-type neurons, which express TTX-S exclusively, served as a model for dynamic current-clamp (DCC) simulation, in which gNa0 (TTX-S) and gNa1 (TTX-R) were injected separately or in combination. RESULTS: peak, and progressively impaired repetitive firing, whereas the TTX-S peak remained unchanged. CONCLUSION: channels coordinate AP depolarization sequentially and compensatorily: TTX-S initiates the upstroke, whereas TTX-R is recruited later and reactivates during repolarization to constrain firing frequency. Combining patch-clamp with DCC simulation provides novel insight into visceral sensory neuron excitability.