这本书的用词会让人产生混淆 就我的理解, 参考braunward 9th ch35 像Na/K/Ca 这一类voltage gated ion channel皆以三种形式存在 (有些药理的书也会提到 e.g. Katzung) (voltage gated意指channel 打开受cell membrane potential 影响 cell membrane depolarization时才打开) 1. open/activated state (cell membrane depolarization才打开 这本书上写成:open, depolarized channels) 2. closed/inactivated state (Ca channel 在打开後, 就会直接进入 closed/inativated state, 这个state 无法再度被活化) 3. closed/resting state(cell membrane repolarization後, Ca channel 才会从closed inativated state进入close resting state 此状态下的channel 才可以再度被活化) 就因为Verapamil and ditiazem 只会抑制open/activated calcium cnannel 所以才叫use-dependent,而且不让open/ativated calcium channel 回到 close/resting state (原文写prevent repolarization,应该就是不让calcium channel回到closed/resting state, 而不是指prevent cell menbrane repolarization) 因为verapamil/diltaizem主要的作用就是抑制Ca流入细胞, 整体而言是会"加速" cell membrane repoalrization, 但因为抑制calcium channel回到 close/resting state, 对下一个actional potential cycle而言, 可 以活化的calcium channel变少了, 因此会增加effective refractory period, 亦即传导速度变慢) ※ 引述《hpw01 (hpw)》之铭言： : 在Lippincotts Illustrated Reviews Pharmacology第十七章提到 : 关於第四类抗心律不整药物Verapamil and diltiazem的机转: : Actions: Calcium enters cells by voltage-sensitive channels and by : receptor-operated channels that are controlled by the binding of agonists, : such as catecholamines, to membrane receptors. Calcium-channel blockers, such : as verapamil and diltiazem, are more effective against the voltage-sensitive : channels, causing a decrease in the slow inward current that triggers cardiac : contraction.以上可以读懂 : Verapamil and diltiazem bind only to open, depolarized channels, : thus preventing repolarization until the drug dissociates from the channel. : 这边开始不懂了 : 为什麽只接在打开跟去极化的通道会防止通道的再极化? : These drugs are therefore use-dependent; that is, they block most effectively : when the heart is beating rapidly, because in a normally paced heart, the : calcium channels have time to repolarize and the bound drug dissociates from : the channel before the next conduction pulse. : 不太理解甚麽叫做钙离子通道的再极化 : 书上讲动作电位有一个图将Action potential of a Purkinje fiber分成 : 0 1 2 3 4 五个phase : 其中phase3再极化时作用的不是主要是钾离子吗?跟钙离子有甚麽关系呢? : 最後一段(前面的问题解决了应该就懂了,打上来帮助理解) : By decreasing the inward current carried by calcium, : verapamil and diltiazem slow conduction and : prolong the effective refractory period in tissues that are dependent on : calcium currents, such as the AV node. These drugs are therefore effective in : treating arrhythmias that must traverse calcium-dependent cardiac tissues. : 书上还提到Verapamil and diltiazem治疗心房性心律不整比心室性心律不整有效 : 请问是为什麽呢? 最後一个问题, 我的理解是verapamil and diltiazem主要作用於SA node and AV node, 心房性心律不整, 一定要经过AV node 传到心室, 才会造成心搏过快 因此只要抑制AV node整体速度就会降下来, 反观心室性心律不整并不需要AV node就可以跳, 因此你抑制SA node or AV node,对心室性心律不整没有帮助. --

※ 发信站: 批踢踢实业坊(ptt.cc) ◆ From: 114.34.109.233 ※ 编辑: sophiajoan 来自: 114.34.109.233 (07/30 20:45)