The Effects Of Tyramine On A-type Potassium Currents And The Related Ionic Channel Mechanisms In Small Trigeminal Ganglion Neurons In Mice

Objective: To investigate the effect of tyramine on the voltage dependent A-type potassium currents and the underlying mechanisms in trigeminal ganglion neurons in mouse.Methods:The trigeminal ganglia neurons in mouse were isolated by eollagenase. the effect of Tyamine on A-type K currents(A-currents)in small trigeminal ganglion neurons(TGN) were determined by whole cell patch clamp technique and pharmacological methods were used to clarify its related underlying signaling pathways.Results:1)Type A potassium current was dose-dependently inhibited by tyramine from 1μM to 0.0001μM, and the inhibition rate was(48.21±11.72)%,(32.25±2.07)%,(23.84±2.69)%,(16.26±2.72)% and(7.07±2.91)%. 2)respectively. After elution of tyramine, the amplitude of type A potassium current partially recovered to the pretreatment, whereas the sustained delayed rectifie r potassium channel and sodium channel were not significantly affected by 0.1μM tyramine. In the meantime. 0.1μM tyramine had a minor inhibition on the calcium channel(11.3±4.97)%. 3)0.1μM tyramine could also increase the discharge frequency of trigeminal ganglia neurons. 4)when extracellular fluid was added GDP-βs, a selective G protein antagonist, the effects also could be blocked.5)we observed that the related downstream signaling pathways i n the cell, PKA inhibitor of PKI6-22 have no influence in tyramine induced A-type potassium current, tyramine induced A-type potassium current can be only blocked by PKCθ.Conclusions:Tyramine inhibited A-currents in a concentration-dependent manner. Tyramine enhanced excitability of TGN through down-regulation of type A potassium current. And their role is via G protein coupled PKCθ pathways.