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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}}
|QuestionAuthor={{Rim}} (Reviewed by Serge Korjian)
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Physiology
|MainCategory=Physiology
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|MainCategory=Physiology
|MainCategory=Physiology
|SubCategory=Cardiology
|SubCategory=Cardiology
|MainCategory=Physiology
|MainCategory=Physiology
|MainCategory=Physiology
|MainCategory=Physiology
|MainCategory=Physiology
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|MainCategory=Physiology
|MainCategory=Physiology
|SubCategory=Cardiology
|SubCategory=Cardiology
|Prompt=A pharmaceutical company develops a new anti-arrhythmic drug that targets the slow voltage gated potassium channels. Shown below is an image depicting the ventricular action potentialWhich of the following phases of the action potential, labelled from A to E, corresponds to the target of the new drug?
|Prompt=A pharmaceutical company is developing a new anti-arrhythmic drug that targets the slow voltage gated potassium channels.  During which of the following phases of the action potential (depicted below) is this drug most active?


[[File:Ventricular action potential question.png]]
[[File:WBR1015.png]]
|Explanation=The ventricular action potential is composed of four phases:<br>
|Explanation=The ventricular action potential is composed of four phases:
- Phase 0 ([[depolarization]]): abrupt opening of the voltage gated sodium channel<br>
* Phase 0 (depolarization): abrupt opening of the voltage gated sodium channel
- Phase 1 (early repolarization): closure of the sodium channels and opening of voltage gated potassium channels<br>
* Phase 1 (early repolarization): closure of the sodium channels and opening of voltage gated potassium channels
- Phase 2 (plateau): opening of the voltage gated calcium channels leading to an influx of calcium that balances the potassium efflux<br>
* Phase 2 (plateau): opening of the voltage gated calcium channels leading to an influx of calcium that balances the potassium efflux
- Phase 3 (rapid repolarization): closure of the calcium channels and opening of the slow voltage gated potassium channel<br>
* Phase 3 (rapid repolarization): closure of the calcium channels and opening of the slow voltage gated potassium channel
- Phase 4 ([[resting potential]]): high potassium permeability through the potassium channels<br>
* Phase 4 (resting potential): high potassium permeability through the potassium channels
Shown below is an image depicting the different phases of the ventricular action potential.
The image below details the different phases of the ventricular action potential.


[[File:Ventricular action potential.png]]
[[File:Ventricular action potential.png]]
'''Education objective:'''
The phase 3 of the ventricular action potential is characterized by a rapid repolarization caused by the closure of the calcium channels and opening of the slow voltage gated potassium channel.
'''Reference:'''
First aid for USMLE step 1, 2014.  Page 274.
|AnswerA=A
|AnswerA=A
|AnswerAExp=A corresponds to phase 0 of the [[ventricular action potential]].  Phase 0 is characterized by a [[depolarization]] caused by the abrupt opening of the voltage gated sodium channel.
|AnswerAExp=A corresponds to phase 0 of the ventricular action potential.  Phase 0 is characterized by a depolarization caused by the abrupt opening of the voltage gated sodium channel.
|AnswerB=B
|AnswerB=B
|AnswerBExp=B corresponds to phase 1 of the [[ventricular action potential]].  Phase 1 is characterized by an early repolarization caused by the closure of the sodium channels and the opening of voltage gated potassium channels.
|AnswerBExp=B corresponds to phase 1 of the ventricular action potential.  Phase 1 is characterized by an early repolarization caused by the closure of the sodium channels and the opening of voltage gated potassium channels.
|AnswerC=C
|AnswerC=C
|AnswerCExp=C corresponds to phase 2 of the [[ventricular action potential]].  Phase 2 is characterized by a plateau.  The plateau results from the opening of the voltage gated calcium channels leading to an influx of calcium that balances the potassium efflux.
|AnswerCExp=C corresponds to phase 2 of the ventricular action potential.  Phase 2 is characterized by a plateau.  The plateau results from the opening of the voltage gated calcium channels leading to an influx of calcium that balances the potassium efflux.
|AnswerD=D
|AnswerD=D
|AnswerDExp=D corresponds to phase 3 of the [[ventricular action potential]].  Phase 3 is characterized by a rapid repolarization caused by the closure of the calcium channels and opening of the slow voltage gated potassium channel.
|AnswerDExp=D corresponds to phase 3 of the ventricular action potential.  Phase 3 is characterized by a rapid repolarization caused by the closure of the calcium channels and opening of the slow voltage gated potassium channel.
|AnswerE=E
|AnswerE=E
|AnswerEExp=E corresponds to phase 4 of the [[ventricular action potential]].  Phase 4 is characterized by a [[resting potential]] which is caused by the high potassium permeability through the potassium channels.
|AnswerEExp=E corresponds to phase 4 of the ventricular action potential.  Phase 4 is characterized by a resting potential which is caused by the high potassium permeability through the potassium channels.
|EducationalObjectives=The phase 3 of the ventricular action potential is characterized by a rapid repolarization caused by the closure of the calcium channels and opening of the slow voltage gated potassium channel.
|References=First Aid for USMLE Step 1, 2014 page 274
|RightAnswer=D
|RightAnswer=D
|WBRKeyword=Action potential
|WBRKeyword=Action potential, Antiarrhythmics, Phase 3, Calcium channels, Potassium chanels, Mechanism of action
|Approved=No
|Approved=Yes
}}
}}

Revision as of 22:17, 16 August 2015

 
Author [[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Serge Korjian)]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Physiology
Sub Category SubCategory::Cardiology
Prompt [[Prompt::A pharmaceutical company is developing a new anti-arrhythmic drug that targets the slow voltage gated potassium channels. During which of the following phases of the action potential (depicted below) is this drug most active?

]]

Answer A AnswerA::A
Answer A Explanation AnswerAExp::A corresponds to phase 0 of the ventricular action potential. Phase 0 is characterized by a depolarization caused by the abrupt opening of the voltage gated sodium channel.
Answer B AnswerB::B
Answer B Explanation AnswerBExp::B corresponds to phase 1 of the ventricular action potential. Phase 1 is characterized by an early repolarization caused by the closure of the sodium channels and the opening of voltage gated potassium channels.
Answer C AnswerC::C
Answer C Explanation AnswerCExp::C corresponds to phase 2 of the ventricular action potential. Phase 2 is characterized by a plateau. The plateau results from the opening of the voltage gated calcium channels leading to an influx of calcium that balances the potassium efflux.
Answer D AnswerD::D
Answer D Explanation AnswerDExp::D corresponds to phase 3 of the ventricular action potential. Phase 3 is characterized by a rapid repolarization caused by the closure of the calcium channels and opening of the slow voltage gated potassium channel.
Answer E AnswerE::E
Answer E Explanation AnswerEExp::E corresponds to phase 4 of the ventricular action potential. Phase 4 is characterized by a resting potential which is caused by the high potassium permeability through the potassium channels.
Right Answer RightAnswer::D
Explanation [[Explanation::The ventricular action potential is composed of four phases:
  • Phase 0 (depolarization): abrupt opening of the voltage gated sodium channel
  • Phase 1 (early repolarization): closure of the sodium channels and opening of voltage gated potassium channels
  • Phase 2 (plateau): opening of the voltage gated calcium channels leading to an influx of calcium that balances the potassium efflux
  • Phase 3 (rapid repolarization): closure of the calcium channels and opening of the slow voltage gated potassium channel
  • Phase 4 (resting potential): high potassium permeability through the potassium channels

The image below details the different phases of the ventricular action potential.


Educational Objective: The phase 3 of the ventricular action potential is characterized by a rapid repolarization caused by the closure of the calcium channels and opening of the slow voltage gated potassium channel.
References: First Aid for USMLE Step 1, 2014 page 274]]

Approved Approved::Yes
Keyword WBRKeyword::Action potential, WBRKeyword::Antiarrhythmics, WBRKeyword::Phase 3, WBRKeyword::Calcium channels, WBRKeyword::Potassium chanels, WBRKeyword::Mechanism of action
Linked Question Linked::
Order in Linked Questions LinkedOrder::