Effect of high-frequency membrane potential alternation between depolarization and hyperpolarization on dorsal root ganglion neurons of rats

The purpose of this study was to determine how sensory neurons respond to high-frequency membrane potential alternation between depolarization and hyperpolarization. Membrane currents were recorded from dissociated dorsal root ganglion (DRG) neurons of adult rats using the whole cell patch clamp technique in voltage clamp mode. Stepwise depolarization of the membrane was applied first to determine the threshold membrane potential for inducing an action potential (AP) current. Then, membrane potential alternation between depolarization (to +20 mV) and hyperpolarization (to -110 mV) was applied to the neuron for 10 s at different frequencies (10 Hz to 1 kHz). The tested DRG neurons had APs of either a long duration (>10 ms) or a short duration (<10 ms). Membrane potential alternation at >= 500 Hz completely disrupted the AP generation, disabled the ion channel gating function, and produced membrane current alternating symmetrically across zero. Replacing extracellular sodium with potassium increased the amplitude of the membrane current response and caused the membrane current to be larger during hyperpolarization than during depolarization. These results support the hypothesis that high-frequency biphasic stimulation blocks axonal conduction by driving the potassium channel open constantly. Understanding neural membrane response to high-frequency membrane potential alternation is important to reveal the possible mechanisms underlying axonal conduction block induced by high-frequency biphasic stimulation.