Cardiac contraction

Question 1

What are the stages of heart contraction? [5 marks]

Answer 1

• Depolarisation via sodium
• VGCCs open at +30mV
• Plateau with CICR happens
• Slight repolarisation due to Na+/K+ pumps
• Potassium channels open and repolarisation occurs

Question 2

What is the diastolic intracellular concentrations of Ca2+? [1 mark]

Answer 2

0.1μM

Question 3

What are the systolic concentration of Ca2+? [1 marks]

Answer 3

1μM to 10μM

Question 4

What does an increase in Ca2+ result in? [1 mark]

Answer 4

Increased force of contraction

Question 5

How do myocytes contract? [6 marks]

Answer 5

• 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

Question 6

What happens with myosin and actin? [5 marks]

Answer 6

• 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

Question 7

What does troponin T bind to? [1 mark]

Answer 7

Tropomyosin

Question 8

What does troponin I bind to? [1 mark]

Answer 8

Actin filaments

Question 9

What does troponin C bind to? [1 mark]

Answer 9

Calcium

Question 10

What are important blood plasma markers for cardiac cell death? [2 marks]

Answer 10

• Troponin I

- Troponin T

Question 11

How does the intracellular concentration of Ca2+ decrease? [5 marks]

Answer 11

• 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

Question 12

What levels of control exist for stretch? [2 marks]

Answer 12

Extrinsic: increase in intracellular [Ca2+]
Intrinsic: increased pressure or volume

Question 13

What happens to contractility and end diastolic pressure as muscle is stretched? [2 marks]

Answer 13

• They increase

- Due to more actin binding sites exposed

Question 14

What do sympathetic mimetics do to increase intracellular [Ca2+]? [1 mark]

Answer 14

Increase VGCC activity

Question 15

What do cardiac glycosides do to increase intracellular [Ca2+]? [1 mark]?

Answer 15

Reduce Ca2+ outflow

Question 16

What do positive inotropes do? [1 mark]

Answer 16

They increase the energy/strength of contraction

Question 17

What does GPCRs with alpha s do? [3 marks]

Answer 17

• Stimulates adenyl cyclase to convert ATP to cAMP

- cAMP converts inactive protein kinase A to active protein kinase A

Question 18

What breaks down cAMP? [1 mark]

Answer 18

Phosphodiesterase

Question 19

What does protein kinase A do? [5 marks]

Answer 19

• Phosphorylates calcium channel
• Makes contraction greater
• Increases opening of K+ so faster repolarisation
• Increases heart beat
• increases Ca+ ATPase activity

Question 20

What does digitalis do to reduce Ca+ outflux? [2 marks]

Answer 20

• Inhibits Na+/K+ ATPase so Na+ builds up in the cell

- So there’s less K+ potential outside, less calcium comes in

Question 21

What are examples of β-adrenoceptor stimulants? [2 marks]

Answer 21

• Dobutamine

- Dopamine

Question 22

What is an example of a Gs stimulator? [1 mark]

Answer 22

Glucagon

Question 23

What is an example of a phosphodiesterase inhibitor? [1 mark]

Answer 23

Amrinone (only in extreme cases)