The Research In Mechanism Of Small Conductance Ca²⁺-activated K⁺channels SK3 In The Trigeminal Neuropathic Pain

Objective:The structure and function of ion channels on the neuron cell membrane are closely related to the occurrence of pain.Researches have shown that small conductance Ca²⁺-activated K⁺channels 3?SK3channels?encoded by KCNN3 gene polymorphism which induced by poly glutamine repeated CAG is related with migraine.Other studies suggested that migraine and trigeminal neuralgia?TN?have similar pain conduction pathway,thus we speculated that SK3 channel may be involved in the occurrence of TN.So this paper was designed to detect?1?Whether SK3 channel exists in normal rat trigeminal ganglion?TG?.?2?The expression changes of SK3 channel in TG in rats with TN.?3?Effect of SK3 channel agonists and inhibitors on rats'facial mechanical threshold in rats with TN.This paper aims to provide a new target for the treament of TN.Methods:1.The expression of SK3 channel in normal rats TG:Five healthy adult male SD rats,weight 200-250g,decapitated liver,TG and DRG,SK3 channels protein and mRNA were detected by Western blot and PCR.2.The expression changes of SK3 channel in TG in rats with TN:Thirty healthy adult male SD rats,weight 200-250g,were randomly?the random number method?divided into two groups:Infraorbital nerve ligation group?I group,n=20?and sham group?S group,n=20?.Infraorbital nerve was exposed and ligated by the zygomatic approach in I group.Infraorbital nerve was exposed,without ligation in S group.Facial mechanical threshold was detected in two groups before and after surgery to 1,5,10,15,30,45,60 day?n=10?.On the 15 day after operation,the SK3 channel protein was detected by immunofluorescence Western blot and PCR in each group?n=30?.3.Effect of SK3 channel agonist CyPPA and inhibitor apamin on rats with TN:Sixty healthy adult male SD rats,weight 200-250g,were randomly?the random number method?divided into two groups:Infraorbital nerve ligation group?I group,n=30?and sham group?S group,n=30?.I group and S group were received above procedures respectively.On the 15 day after operation,the rats in each group were injected with different doses of SK3 channel agonist CyPPA and inhibitor apamin via the infraorbital foramen injection into theTG.There were six subgroups in total according to different dose and medicine:CyPPA20ug?C1=5?,50ug?C2=5?,100ug?C3=5?;apamin2ug?0.1ml,A=5?;CyPPA100ug+apamin?AC=5?and0.9%NS0.1ml?NS=5?.Facial mechanical thresholds were detected before injection?T0?and 20min?T1?,40min?T2?,60min?T3?,80min?T4?,100min?T5?,120min?T6?after injection.Results:1.The expression of SK3 channel was found in TG in normal rats:SK3 channel in TG is higher than DRG,but lower than liver.The differences between two groups have statistical significance?P<0.05?;2.The changes of facial mechanical threshold preoperative and postoperative in rats of I group:13±2.74g preoperative,21±2.02g 1d after surgery,from the 5d 16.4±1.67g reduced to 15d 0.090.06g?lowest?,then from 30d to recover until 60d 6.8±1.28g.There were significant differences among all time points?P<0.05?.Pain threshold was no significant difference among all time points in S group?P>0.05?.Comparison between two groups:pain threshold had no significant differences before and 5d after operation?P>0.05?.The pain threshold of I group was lower than S group at other time points?P<0.05?.3.The expression changes of SK3 channel in TG in rats with TN:On the 15d after operation,the expression of SK3 channel detected by immunofluorescence?Western blot and PCR in operation group was lower than that in sham group?P<0.05?.4.Effect of CyPPA and apamin on pain threshold in rats with TN:Comparison between groups in operation group:The pain threshold was no difference between groups before injection?P>0.05?;20min after injection:C1,C2,C3 were higher than the NS group?P<0.05?,and C3group was highest?P<0.05?.There were no significant differences among other goups?P>0.05?.40min after injection:C2 group and C3 group were higher than NS group.A group and C3 group were higher than AC group?P<0.05?.There were no significant differences among other goups?P>0.05?.60,80min after injection:C2 group and C3 group were higher than other groups?P<0.05?.There were no significant differences among other goups?P>0.05?.100min after injection:C3 group was higher than C1,A,AC group?P<0.05?.There were no significant differences among other goups?P>0.05?.120min after injection:C2 group and C3 group were higher than NS group and A group.Comparison in each group:The change of pain threshold in NS group was not statistically significant at all time points?P>0.05?;C1 group:T3,T4,T5 were higher than other time points and T4 point was higher than T3 and T5 point?P<0.05?.C2group:T3 was higher than T0,T1?P<0.05?.Other point difference was not statistically significant?P>0.05?.C3 group:T3 was higher than other each point?P<0.05?.A group:T0 was lower than other time points?P<0.05?.There were no statistically significant within AC group and NS group?P>0.05?.There were no significant difference among all time points in sham operation group.?P>0.05?.Conclusions:1.SK3 channel is present in TG;2.TN model induced by infraorbital nerve ligation can lead to decreased expression of SK3channel in TG;3.SK3 agonist CyPPA could increase facial mechanical threshold 20-60min after injection,decreased 80-120min after injection;SK3 inhibitor apamin could decreased facial mechanical threshold20-40min after injection,increased gradually 80-120min after injection.Injecting agonist CyPPA after injecting inhibitor is higher than injecting inhibitor group.It is suggested that SK3 channel may be a potential target for studying TN.