- 學位論文
四烷基銨離子對視丘下核神經元回返性鈉離子電流之抑制作用
The Inhibitory Effects of Tetra-alkylammonium Ions on Resurgent Sodium Currents in Subthalamic Neurons
摘要
中樞神經系統的電氣活動掌控了人的知覺處理、思考記憶以及運動行為等功能，而這些電氣活動的發生基礎則是神經細胞上各種離子通道的活性表現。視丘下核是大腦皮質－基底核迴路系統中的一個重要樞紐，該核區細胞的放電模式會影響運動行為的調控。視丘下核神經細胞上的鈉離子通道被發現具有產生回返性鈉離子電流的特性，然而為何鈉離子通道能產生回返性鈉離子電流，雖然過去已有學者提出假說，但回返性鈉離子電流的諸多生物物理性質無法被該假說解釋完備。本實驗以離體的視丘下核神經元為材料，以全細胞電壓箝制技術進行實驗，利用結構單純明確之物質：四烷基銨類離子、精胺、以及鎂離子等作為分子探針，觀察細胞內加入上述這些物質後對於回返性鈉離子電流的影響，藉此探討視丘下核細胞鈉離子通道產生回返性鈉離子電流的可能分子機制。實驗結果顯示，於細胞內加入0.1毫莫耳之四烷基銨類離子後，會對回返性鈉離子電流造成不同程度的抑制。其中四戊基銨離子與四丁基銨離子的效果最強，回返性鈉離子電流可被完全抑制，然而暫時性鈉離子電流則僅受到部分或較微小之抑制；而四己基銨離子則可抑制一部份之回返性鈉離子電流；其他如四乙基、四丙基與四庚基銨離子則幾乎不影響回返性鈉離子電流之大小。至於精胺，實驗結果發現當視丘下核細胞內加入1毫莫耳之精胺後，會稍影響回返性鈉離子電流之大小，但未達統計上之顯著，其生理意義也需要進一步釐清。最後，針對鎂離子的實驗，改變視丘下核細胞內之鎂離子濃度，並不影響回返性鈉離子電流的大小與其基本性質。這些結果顯示，回返性鈉離子電流應係由一不同於短暫性鈉離子電流之開啟態通道所造成。
並列摘要
The electrical activities in the central nervous system constitute the bases of perceptual processing, motor behavior, thinking and memory. The subthalamic nucleus (STN) is an important hub in the cortico-basal ganglia circuit. The firing pattern of STN neurons may be shifted between the tonic and the burst mode. It has been demonstrated that the voltage-gated sodium channels in STN neurons would give rise to a resurgent current during the repolarization phase following a depolarization period. The molecular mechanism underlying the genesis of resurgent currents, however, is not fully clear. We performed whole-cell voltage clamp in dissociated rat STN neurons. Cations with simple and defined structures such as tetra-alkylammoniums, spermine, and Mg2+ ions were used to probe the molecular events responsible for the resurgent currents. We found that the resurgent currents are completely abolished but the transient currents are relatively unaffected when 0.1 mM of tetrabutylammonium (TBuA) or tetrapentylammonium (TPenA) was introduced into the STN neuron. On the other hand, 0.1 mM tetrahexylammonium (THexA) could only partly inhibit the resurgent currents. 0.1 mM tetraethylammonium (TEA), tetrapropylammonium (TPrA), or tetraheptylammonium (THepA) had no discernible inhibitory effect on resurgent currents. Finally, the resurgent currents were not significantly influenced by intracellular spermine or Mg2+. These results indicate that the resurgent sodium current should be ascribable to an open channel state distinct from that responsible for the transient sodium current.