Combinatorial logic of Nav channels in nociceptor excitability: Different degrees of synergy define distinct neuronal groups.

Despite the genetic validation of voltage-gated sodium (Nav) channels as targets for pain therapy, single-channel subtype inhibition in clinical trials has yielded limited efficacy. Because Nav1.7 and Nav1.8 are thought to act in a coupled manner in ignition and subsequent regenerative, overshooting depolarization underlying the action potential of nociceptors, we utilized dynamic clamp, which permits precisely calibrated addition or subtraction of the current from any given channel, to systematically interrogate their combinatorial landscape. We demonstrate that nociceptor excitability is governed by highly non-linear biophysical rules. Partial, simultaneous attenuation of both conductances drives a supralinear collapse of action potential electrogenesis in sensory neurons. Unsupervised clustering reveals that this synergistic vulnerability is not a continuum, but varies in different neuronal subtypes: a population of sensory neurons experiences profound excitability suppression, whereas another population remains relatively resistant. These non-linear boundaries demonstrate that the efficacy of Nav current abrogation is fundamentally restricted by the underlying electrogenic architecture of the neuron, and provide a mechanistic blueprint for subtype-selective silencing.