大鼠A7核區兒茶酚胺神經細胞中A型鉀離子通道之功能探討

Abstract

橋腦中A7正腎上腺素神經核在痛覺傳遞的調控上扮演了很重要的角色，本論文為第一次對此正腎上腺素神經元所表現之A型鉀離子電流進行電生理、藥理特性及功能上的探討。此A型鉀離子電流活化閾值約在 -70 mV，半活化電位為-27.97 ± 1.71 mV，半不活化電位為 -72.31 ± 2.27 mV。此A型鉀離子電流從不活化回復非常快，在Vm = -100 mV時其回復時間長數為 21.87 ± 2.80 ms。對Kv4專一之抑制劑heteroprodotoxin2 (HpTx2)可顯著抑制此A型鉀離子電流，但是此電流不受到Kv3.4 專一之抑制劑 BDS-I所影響。此電流之生物物理及藥理特性結果顯示：A7正腎上腺素神經元之A型鉀離子電流是由Kv4次單元組成。以免疫組織化學染色方法發現Kv4.3鉀離子通道蛋白表現在A7正腎上腺素神經元之細胞本體及主要樹突上，顯示此A型鉀離子通道可能為Kv4.3所組成。此A型鉀離子通道不僅調控A7正腎上腺素神經元之動作電位的延遲產生及放射動作電位的瞬時頻率，更參與調控動作電位之寬度。實驗結果更進一步地證實：此A型鉀離子通道可被興奮性突觸後電位變化所活化，並可能在突觸訊號的傳遞與整合上扮演了重要的角色。此論文之研究結果讓我們對A7正腎上腺素神經元的電生理特性有更進一步的了解，對於A型鉀離子電流在痛覺的調控上也提供了一個可能的機制。

The pontine noradrenergic (NAergic) neurons located in A7 area are believed to play an important role in modulating nociception. This study provides the first functional analysis of the biophysical and pharmacological properties of A-type current (IA) in A7 NAergic neurons. IA in A7 NAergic neurons was activated at about -70 mV, with midpoint activation potential of -27.97 ± 1.71 mV. The midpoint inactivation potential was at about -72.31 ± 2.27 mV, and the recovery from inactivation was very quickly with a time constant of 21.87 ± 2.80 ms at Vm = -100 mV. The IA was sensitive to heteroprodotoxin2 (HpTx2), a Kv4 selective blocker, but not affected by BDS-I, a Kv3.4 selective blocker. These biophysical and pharmacological results demonstrated that A-type current in A7 NAergic neurons is mediated mainly by Kv4. By immunostaing, we found that Kv4.3 proteins were robustly expressed on the soma and dendrites. This result indicated that the A-type in A7 NAergic neurons may mediated by somatodendritic Kv4.3. This A-type current acted not only at subthreshold level to control the initiation of action potential and firing frequency, but was also activated at suprathreshold to shape the action potentials. Furthermore, it could be activated by membrane depolarization during excitatory synaptic transmission and might contribute to the synaptic signal propagation and integration in A7 NAergic neurons. These findings may help us understand more about the regulation of pain transmission.