在Lippincotts Illustrated Reviews Pharmacology第十七章提到 關於第四類抗心律不整藥物Verapamil and diltiazem的機轉: 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.以上可以讀懂 Verapamil and diltiazem bind only to open, depolarized channels, thus preventing repolarization until the drug dissociates from the channel. 這邊開始不懂了 為什麼只接在打開跟去極化的通道會防止通道的再極化? 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. 不太理解甚麼叫做鈣離子通道的再極化 書上講動作電位有一個圖將Action potential of a Purkinje fiber分成 0 1 2 3 4 五個phase 其中phase3再極化時作用的不是主要是鉀離子嗎?跟鈣離子有甚麼關係呢? 最後一段(前面的問題解決了應該就懂了,打上來幫助理解) 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. 書上還提到Verapamil and diltiazem治療心房性心律不整比心室性心律不整有效 請問是為什麼呢? --

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