Cardiac contraction Flashcards
What are the stages of heart contraction? [5 marks]
- Depolarisation via sodium
- VGCCs open at +30mV
- Plateau with CICR happens
- Slight repolarisation due to Na+/K+ pumps
- Potassium channels open and repolarisation occurs
What is the diastolic intracellular concentrations of Ca2+? [1 mark]
0.1μM
What are the systolic concentration of Ca2+? [1 marks]
1μM to 10μM
What does an increase in Ca2+ result in? [1 mark]
Increased force of contraction
How do myocytes contract? [6 marks]
- VGCCs open
- Calcium comes in and binds to ryanodine receptors at SR
- CICR at SR
- Calcium binds to TnC, which changes the shape of tropomyosin
- Myosin binds to actin binding sites
- ATPase in myosin head release energy and slides filaments
What happens with myosin and actin? [5 marks]
- Cross bridge
- Myosin head bends and ADP+Pi are released
- ATP attaches to head which detaches from actin
- ATP is hydrolysed and myosin springs back
- Filament slides along
What does troponin T bind to? [1 mark]
Tropomyosin
What does troponin I bind to? [1 mark]
Actin filaments
What does troponin C bind to? [1 mark]
Calcium
What are important blood plasma markers for cardiac cell death? [2 marks]
- Troponin I
- Troponin T
How does the intracellular concentration of Ca2+ decrease? [5 marks]
- VGCCs close
- no CICR
- 30% of calcium leave via Na+/Ca2+ exchanger
- 70% of calcium go back to SR via Ca2+ ATPase
- Mitochondria uptakes calcium
What levels of control exist for stretch? [2 marks]
Extrinsic: increase in intracellular [Ca2+]
Intrinsic: increased pressure or volume
What happens to contractility and end diastolic pressure as muscle is stretched? [2 marks]
- They increase
- Due to more actin binding sites exposed
What do sympathetic mimetics do to increase intracellular [Ca2+]? [1 mark]
Increase VGCC activity
What do cardiac glycosides do to increase intracellular [Ca2+]? [1 mark]?
Reduce Ca2+ outflow
What do positive inotropes do? [1 mark]
They increase the energy/strength of contraction
What does GPCRs with alpha s do? [3 marks]
- Stimulates adenyl cyclase to convert ATP to cAMP
- cAMP converts inactive protein kinase A to active protein kinase A
What breaks down cAMP? [1 mark]
Phosphodiesterase
What does protein kinase A do? [5 marks]
- Phosphorylates calcium channel
- Makes contraction greater
- Increases opening of K+ so faster repolarisation
- Increases heart beat
- increases Ca+ ATPase activity
What does digitalis do to reduce Ca+ outflux? [2 marks]
- Inhibits Na+/K+ ATPase so Na+ builds up in the cell
- So there’s less K+ potential outside, less calcium comes in
What are examples of β-adrenoceptor stimulants? [2 marks]
- Dobutamine
- Dopamine
What is an example of a Gs stimulator? [1 mark]
Glucagon
What is an example of a phosphodiesterase inhibitor? [1 mark]
Amrinone (only in extreme cases)
