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Lecture 11 - EC Coupling

Lecture 11 - EC Coupling - L ecture 11 EC Coupling The...

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Lecture 11 – EC Coupling The electrical excitation of the heart triggers the mechanical contraction Electrifying the pump - Electricians --- > Plumbers - EKG, Arrhythmias, ion channels - perfusion & pumping, heart attacks, heart failure, sarcomere (Ca+ + in the SR) - The electrical excitation of the heart triggers the mechanical contraction. Action Potential Redux (The electrician - When a myoctye gets excited, the sodium channels open up, which allows for the depolarization to occur. - Then there is an initial repolarization through the Ito channels (transient - Followed by L-type calcium channels and the delayed rectifier channels opening in phase 2 (Ca goes in, K goes out, and they are about equal during the plateua phase). - The lecturer will focus on phase 2, when calcium comes into the cardiac myoctye - Other channels are important, like the K channels: they allow for repolarization to occur after this plateau phase Relationship between Ca++ and contraction - This excitation corresponds to the phase 2 - The cardiac mycotye is contracting, get sudden rise of intracellular calcium when the cell gets excited, this leads to - As calcium decreases, the myoctye starts relaxing during the repolarization phase - Calcium is critical factor Actin Myosin (The Plumbers) - Sarcomeres (major contractile components) are comprised of the thin actin filaments and the thick myosin - These sarcomeres are throughout the cardiac mycotye and are interconnected so that when the mycotye is electrically excited, contraction occurs in all the - When not excited, relaxation occurs (myosin head will not allow contact with - Relaxation is critical: heart needs to be able to relax in order to fill blood. If there is a relaxation problem can lead to diastolic heart failure . Heart gets stiff --> leads to backup of Actin-Myosin Crossbridging (Toolbox) - Troponin-Tropomyosin complex intertwined with actin filament, so the actin is blocked and myosin cannot bind to it. - When calcium binds to troponin, tropomyosin is moved so the myosin can - So remember calcium is key Ca ++ Troponin, Tropomysoin (Toolbox) - Myosin binding sites are blocked, then calcium comes and binds to troponin. The troponin/tropomyosin complex turns and exposes the actin. - Magneiusm helps hydrolyze ATP into ADP and P and allows for triggering the mysoin head into position - Now the cross-bridge can occur - Then calcium is released from troponin - The myosin head needs ATP to come off from the myosin or it can’t relax Myosin and ATP (toolbox) ACtin-myosin Crossbridging (toolbox)
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Excitation-Contracting Coupling - Calcium goes through the L type calcium  channel during phase 2 or the plateau  phase of the action potential.  - During diastole, when the myoctye  relaxases, the calcium levels have to be  reduced in the myoctye, so it gets effluxed  Answers: T tubules - How do you get calcium inside the whole  - Use the T tubules to increase the SA of the  myoctye so that you can get calcium near  all of the sarcomeres.
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Lecture 11 - EC Coupling - L ecture 11 EC Coupling The...

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