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Unformatted text preview: 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 cant relax Myosin and ATP (toolbox) ACtin-myosin Crossbridging (toolbox) 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...
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This note was uploaded on 09/14/2011 for the course PHARM cs taught by Professor Staff during the Spring '11 term at UCSD.
- Spring '11