Cardiac Excitation-Contraction Coupling Flashcards
Is the amount of calcium that enters the cardiomyocyte through the voltage gated calcium channel enough to cause contraction?
Yes, but at insufficient levels to maintain a cardiac output that would sustain life.
What are some gross structural differences between cardiac and skeletal muscle? (3)
- longitudinal elements of the tubule system
- Sarcoplasmic reticulum comes in close contact to the tubule system mostly in dyads but can still be in triads
- Cell volume is about 40% mitochondria reflecting near entire dependence on aerobic metabolism
How do ryanodine receptors in cardiac muscle differ than those in skeletal muscle?
They are not physically coupled to the voltage gated calcium channels and rely on calcium induced calcium release to open.
What is the main pump that maintains calcium levels in the cardiac muscle cell?
Na/Ca exchanger (NCX)
How does the activity of the Na/Ca exchanger compare to the Ca ATPase pump?
The NCX is at least an order of magnitude faster.
How is cardiac muscle contractile strength varied?
Change the amount of calcium that enters the cell.
Stimulation of beta 1 receptors causes what changes in the heart? (3)
- Increased chronotropy (heart rate)
- Increased ionotropy (heart contractility)
- Increased lucitropy (rate of relaxation)
Why is a positive lucitropic effect required for a fast heart rate?
It allows the heart to spend less time in systole. Otherwise the heart could only beat faster if it shortened the time in diastole which would eventually dramatically reduce ventricular filling and therefore stroke volume.
