膽鹼性神經元(Cholinergic neurons)


◎膽鹼性神經元釋放Acetylcholine傳遞訊息,可分為Acetyl與Choline兩部分,必須有四級胺存在並且Acetyl與四級胺之間要有2個碳,才能稱為Acetylcholine
◎Acetylcholine早期用以治療高血壓、青光眼、神經性尿滯留、術後尿滯留等疾病


步驟                                               機轉                                          相對應藥物


1. ACh 合成         choline在細胞內合成,必須由細胞膜上 的choline transporter收進入細胞,再由粒 線體的choline acetyltransferase(CAT)合成


Hemicholinium: 抑制 choline transporter因而 減少 ACh 合成


2.攝入儲存小
ACh transporter 將 ACh 運送入突觸小泡
Vesamicol:  抑制
ACh transporter
3.釋放
當刺激傳遞到軸突末梢,鈣離子通道打開,
鈣離子進入膜內,刺激突觸小泡釋放
1.Betulinum toxin(桿菌 毒素):  制 Ach 的釋放

2.Black widow spider venom(黑 寡婦毒素): 促進 Ach 的釋放
4.與受體結合
 和 兩種 receptor

5. ACh 分解
ACh 觸間隙會快速的被 ACh
esterase(AChE)  分解成膽鹼(choline)和醋酸 鹽(acetate)
AChE inhibitor: 抑制 AChE 的作 用
6.膽鹼回收
分解後產生的膽鹼經由 choline transporter 
收再利用


2. 膽鹼酯解酶(choline esterase)
A. 將乙醯膽鹼水解成膽鹼與醋酸鹽,有兩個部位與ACh結合
Anionic site(陰離子位)
Esteratic site(陽離子,脂質水解位)
與膽鹼結合
與醋酸結合

B. 分為acetylcholinesterase(AChE)與pseudocholinesterase(pseudo- ChE)兩類,兩者皆存在於人體內,也都可以是藥物的作用位置(重要!)
註:(pseudo- AChE)改為 (pseudo- ChE)

acetylcholinesterase(AChE)
pseudocholinesterase(pseudo-
AChE)
專一性
有專一性
無專一性
存在位置
型神經接(神經肉結
)或神經節
製造,分至血漿
水解效果
乙醯基>丙醯基>丁醯基
(優先水解乙醯基)
丁醯基>丙醯基>乙醯基
相關作用
神經傳遞重要的酵素(本章介紹
 AchE 都屬此類)
1.診斷 AChEi 的量會不會太高
(e.g.)巴拉(藥,有機磷酸鹽為一 AChEi如果巴松中毒, 可以藉由血漿中 pseudo- ChE 活 性來診斷
2. 觀察投予的 procaine(一種局 部麻醉可被 pseudo- ChE 降 解)的量

二、膽鹼性神經作用
1.存在位置

A. 所有交感、副交感的節前神經元
B. 副交感節後神經末,與支配汗腺的交感節後神經末
C. 體神經末
註:本課著重於副交感節後神經元的作用
2. 下圖注意副交感神經的作用(虛線)與應用

A. 抑制心臟節律、收縮力、跳動力
B.支氣管收縮:慢性阻塞性肺病(COPD)、氣喘病人不能用此類藥,但可使用其拮抗劑來治療
C.縮瞳:副交感神經作用劑可用於治青光眼(詳細之後會再教)
D.促排尿、胃腸蠕動:用於治療術後尿滯留、神經性尿滯留、便秘
E.促淚液分泌:治乾眼症
F. 促胃酸分泌:胃潰瘍患者不能用副交感神經作用劑
3.膽鹼性接受器為突觸後細胞膜上的穿膜蛋白,分為兩類(重要!):
A.尼古丁受器(Nicotinic
receptor)
陽離子性通道
B.毒蕈鹼受器(Muscarinic
receptor)
G 蛋白偶合受器(G-protein couplreceptors)

I、尼古丁受器(Nicotinic receptor)

資料來源:大英百科全書
A. 分為Nm、Nn(Ng)receptor,當ACh結合上尼古丁受器皆會產生興奮作用
B. 存在位置 :
a. Nm存在於NMJ,可接上ACh,造成骨骼肌收縮
b. Nn存在於神經節,可接上ACh、尼古丁, 造成節後神經興奮
c. 腎上腺髓質,屬Nn
C. 型態:

a. 有2個α、β、γ、δ一共5個次單位
b. 當ACh與α次單位結合時,離子通道開啟,鈉離子進入膜內

a. 尼古丁型接受器都有一個共同的特點--> 擁有2個α 次單位(圈起的為特例),目的為與ACh產生結合,打開離子通道
Ⅱ、毒蕈鹼型接受器(Muscarinic Receptors)

資料來源:igem
A. 屬於G蛋白偶合接受器

B. 在所有被突觸後膽鹼性神經纖維(e.g.副交感器官)刺激的反應細胞
C. 形態
a. muscarinic receptor為7次穿膜蛋白,即穿過細胞膜7次
b. 當agonist(ACh)作用下來後會活化G蛋白,G蛋白有3個次單位(αβγ),
G-α subunit有很多種,因此不同G蛋白可能產生不同效果,有抑制型也有興奮型
比較:尼古丁受器僅有興奮形態

▼神經傳導(Nerve conduction) 顯示/隱藏(show/hide)

2 意見:

  1. Acetylcholinesterase, also known as AChE or acetylhydrolase, is a hydrolase that hydrolyzes the neurotransmitter acetylcholine. AChE is found at mainly neuromuscular junctions and cholinergic brain synapses, where its activity serves to terminate synaptic transmission. It belongs to carboxylesterase family of enzymes. acetylcholinesterase

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