How does antidysrhthmic drugs changes the shape of various phases of the cardiac action potential?
drugs such as LIDOCAINE and VERAPAMIL are used. how would you expect the shape of the action potential of a cardiac muscle to be affected by high doses of these agents? please help.. i have some ideas.. but want to be sure!!
Answers:
Think about which ion channels these compound affect.
Lidocaine is a voltage-gated Na+-channel blocker and verapamil is an L-type Ca2+-channel blocker.
Now think about which parts of the cardiac action potential involve these channels. The upstroke of the AP (Phase 0) is caused by opening of VGSCs and the plateau phase by VGCCs. So a high dose of Lidocaine (one that doesn't kill you) will prevent spontaneous APs from occurring out-of-phase with the nodal tissue. It diffuses away in about the right sort of time to allow response to nodal stimulation but not that from ectopic foci.
The plateau phase will be shortened by verapamil and so the AP will be shortened. I think it's used for ventricular fibrillation.
The effect of the drug depends on which class of anti-arrhythmic it is in. It is explained by the link below.
http://en.wikipedia.org/wiki/antiarrhyth.
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Answers:
Think about which ion channels these compound affect.
Lidocaine is a voltage-gated Na+-channel blocker and verapamil is an L-type Ca2+-channel blocker.
Now think about which parts of the cardiac action potential involve these channels. The upstroke of the AP (Phase 0) is caused by opening of VGSCs and the plateau phase by VGCCs. So a high dose of Lidocaine (one that doesn't kill you) will prevent spontaneous APs from occurring out-of-phase with the nodal tissue. It diffuses away in about the right sort of time to allow response to nodal stimulation but not that from ectopic foci.
The plateau phase will be shortened by verapamil and so the AP will be shortened. I think it's used for ventricular fibrillation.
The effect of the drug depends on which class of anti-arrhythmic it is in. It is explained by the link below.
http://en.wikipedia.org/wiki/antiarrhyth.
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