In vitro and intrathecal siRNA mediated KV1.1 knock-down in primary sensory neurons

KV1.1 is a Shaker homologue K+ channel that contributes to the juxta-paranodal membrane conductance in myelinated axons, and is blocked by fampridine (4-aminopyridine), used to treat the symptoms of multiple sclerosis. The present experiments investigate KV1.1 function in primary sensory neurons and A-fibres, and help define its characteristics as a drug-target using sequence specific small-interfering RNAs (siRNAs). siRNA (71 nM) was used to knock-down functional expression of KV1.1 in sensory neurons (> 25 μm in apparent diameter) in culture, and was also delivered intrathecally in vivo (9.3 μg). K+ channel knock-down in sensory neurons was found to make the voltage-threshold for action potential generation significantly more negative than in control (p = 0.02), led to the breakdown of accommodation and promoted spontaneous action potential firing. Exposure to dendrotoxin-K (DTX-K, 10–100 nM) also selectively abolished K+ currents at negative potentials and made voltage-threshold more negative, consistent with KV1.1 controlling excitability close to the nominal resting potential of the neuron cell body, near − 60 mV. Introduction of one working siRNA sequence into the intrathecal space in vivo was associated with a small increase in the amplitude of the depolarising after-potential in sacral spinal roots (p < 0.02), suggesting a reduction in the number of working K+ channels in internodal axon membrane. Our study provides evidence that KV1.1 contributes to the control of peripheral sensory nerve excitability, and suggests that its characteristics as a putative drug target can be assessed by siRNA transfection in primary sensory neurons in vitro and in vivo.