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? --

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