Effects Of Bradykinin On The Sodium Channel Of Dorsal Root Ganglion Neurons

Dorsal root ganglion is the primary afferent neuron transducting the sensory information. Multiple types of ion channel are the basis contributing to the function of DRG. It is well known that the sodium channel is considered to be responsible for producing and spreading action potential. There are two subtypes of sodium channel, TTX-sensitive (TTX-S) and TTX-resistant (TTX-R). In recent years, more research has been focused on the relationship of pain and sodium channel, especially the TTX-R sodium channel. Pain is one of the symptoms during inflammation reaction. This kind of pain is named inflammatory pain, which caused by some inflammation factors, such as serotonin, prostaglandin, histamine, bradykinin. Up to know, it is not clear that how inflammation factors act on the neurons and their processes. Some research indicated that certain inflammation factors also could affect the function of TTX-R sodium channels.The purpose of this study is to observe the effects of bradykinin on the sodium channel and repetitive firing of dorsal root ganglion, in order to elucidate the possible mechanisms involved. We also observed the common effects of bradykinin and prostaglandin E2 on repetitive firing of DRG.The main results are as follow:1. Under physiological conditions, using the patch clamp technique, we recorded the current of the K+, Ca2+, Na+ ion channels.2. By the voltage clamp model, using Ca2+-free extracellular solution contains 100 nM TTX and K+-free intracellular solution, to record the TTX-R sodium current, the TTX-R sodium current was enhance by adding 10nM, 100uM, 1uM, 10uM bradykinin to the extracellular solution. 10uM bradykinin could increase the currentabout 15 per cent. But bradykinin was no effects on TTX-S sodium channel3. By the current clamp model, repetitive firing occurred by 900ms, lOOpA inject current. The frequency increase when add lOnM, lOOnM, IfiM, lOuM bradykinin to the extracellular solution. lOuM bradykinin could increase the frequency about 32 percent.4. Using the same method, the frequency is not changed in PGE2 containing solution. But after pretreatment with 1 |J,M PGE2 for about three minutes, the frequency increased by 30 per cent to 42 per cent in lOuM bradykinin containing solution.Conclusion:1. Bradykinin is able to enhance the TTX-R sodium current and increase the repetitive firing frequency of DRG neurons.2. Bradykinin was no effects on TTX-S sodium current of DRG.3. PGE2 is no directly effects on the DRG neurons, but could increase the ability of action of DRG to bradykinin.4. Our results indicate that bradykinin induced inflammatory pain is likely to through enhance the TTX-R current.