WBR1015

Revision as of 22:17, 16 August 2015 by Sergekorjian (talk | contribs)
Jump to navigation Jump to search
 
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::