The Cholecystokinin-8(CCK-8) Modulate A-type K~+ Channel Currents With The Underlying Mechanisms In Small Dorsal Root Ganglia Neurons In Mice

Objective: To investigate the effects of cholecystokinin-8(CCK-8)on A-type K~+channel currents and excitability and clarify the relevant mechanisms in dorsal root ganglion(DRG)in mice.Methods: Western blotting analysiswas used to identify CCK2 type receptor of the cultured dorsal root ganglia neurons. The whole-cell patch clamp recording was used to investigate the effect of CCK-8 on A-type K~+currents and excitability in small DRG neurons. Behavior tests including von Frey test as well as the hot plate test) were used to define the analgesic effects of CCK-8 in mice.Results: In the present study, we found: 1)CCK2R were endogenously expressed in dorsal root ganglia neurons. 2) CCK-8 inhibited A-type K~+ channel currents in a dose-dependent manner. CCK-8 at 100 nM reversibly inhibited A-type K~+ channel currents by ~25.9%; 3) These effects were blocked by LY225910, a CCK2 R antagonist,while the CCK1 receptor antagonist had no effect. CCK-8-induced A-current effects was also blocked by intracellular application of GDP-β-S, a selective G protein antagonist, PTX, Gi/o antagonist and PI3K(LY294002), whereas inhibition of PKA(PKI6-22)、PLC(U73122)、PKC(GF109203X, chelerythrine chloride, RO31-8220)have no such effects. 4)In current-clamp, we observed a significant increased firing frequency of action potential of small DRG neurons, induced by CCK-8, meanwhile,the effect can be blocked by 4-AP significantly.Conclusions: CCK-8 inhibited A--type K~+channel currents in small DRG neuronsvia Gi/o-protein coupled CCK2 R, PTX-sensitive PI3 K pathway which could contribute to its physiological functions including neuronal excitability,which then modulate the pain pathways.