Effects Of Voltage-gated Potassium Channels On Trigeminal Neuralgia And Its Peripheral Mechanisms

ObjectiveTthis study established a model of trigeminal neuralgia (TN) through the approach from lower edge of cheekbone and to study the functional changes in the voltage-gated potassium currents in the cultured trigeminal ganglion neurons as well as investigate the effects of adenosine triphosphate(ATP) on transient outward potassium current(IA) in order to initially approach the effects of voltage-gated potassium channels on trigeminal neuralgia and its peripheral mechanisms.Methods1. establishing a model of trigeminal neuralgia (TN) Thirty Sprague-Dawley male rats were divided into two groups as the sham-operated (sham) group and the operated group. The TN model was carried out by using a chronic constriction injury of the infraorbital nerve (ION-CCI). With the mechanical stimulation, to investigate the effect of behavioral test in two groups at preoperation and postoperation 3d,6d,9d,12d,15d,21d in order to verify the new method of ION-CCI.2. Electrophysiological test In this part of the experiment, basic on the TN model, observe the functional changes in the voltage-gated potassium currents, including total potassium currents(Itotal), delayed rectifier potassium current (IK) and transient outward potassium current(IA) in the cultured trigeminal ganglion neurons..whole-cell patch clamp recording were used to determine the difference between sham and ION-CCI rats. Then to investigate effects of adenosine triphosphate(ATP) on transient outward potassium current(IA).Results1. Behavioral tests The withdrawl threshold of whisker pad in ION-CCI rat was decreased significantly from 6 d after operation and then maintained until 21 d, with the lowest on the 15th day (p<0.001 vs sham group). The threshold of whisker pad in non-operated side from operated rats was also decreased significantly compared with that in the sham group (p<0.05 vs sham group).2. Electrophysiological test In this study, Total potassium current (Itotal) and delayed rectifier potassium current (IK) were decreased significantly from (12.74±0.92) nA and (9.04±0.88) nA to (5.37±0.45) nA and (4.38±0.50) nA in the TG neurons from ION-CCI rats compared with those in sham rats(p<0.05). The peak of IA was reduced from (3.24±1.70) nA to (2.31±1.20) nA in the TG neurons from non-operated side compared with sham. The peak of IA was reduced significantly from (3.24±1.70) nA to (1.05±0.55) nA in the TG neurons from the operated side compared with sham(p<0.01). And ATP reduced IA activation in 83.33%(15/18)ATP-sensitive neurons(p<0.05) while ATP did not significantly reduce IA activation in some ATP-sensitive neurons(p 0.05). In addition, IA was not significantly reduced at 10 mmol/L or 100 mmol/L in 16.67%(3/18)ATP-insensitive neurons(p0.05).ConclusionThe present study provided a new method of ION-CCI. In this model, the decrease of IA and IK might contribute, at least in part, to the decrease in mechanical pain threshold of whisker pad and the subsequent hyperalgia. ATP reduced IA activation in ATP-sensitive neurons, which might be a possible way to trigeminal neuralgia through inhibition of voltage-gated potassium channels.