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Cardiovascular Science > Excitation contraction coupling in cardiac muscle > Flashcards

Excitation contraction coupling in cardiac muscle Flashcards

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1
Q

What ion concentration is involved in cardiac muscle contraction?

A

Ca2+

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2
Q

What are the similarities between cardiac and skeletal muscle?

A

Both muscle types are striated
Both contain T tubules
Action potentials raise Ca2+ levels
Ca2+ is crucial for contraction

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3
Q

What are the difference s between cardiac and skeletal muscle?

A

Cardiac muscle has a less developed T-tubule and sarcoplasmic reticulum system
Heart contain specialised excitatory tissues
The heart is electrically connected at intercalated discs (gap junctions)
Ventricular action potential is 100x longer than skeletal muscle

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4
Q

What is excitation-contraction coupling?

A

The process whereby action potential triggers myocyte to contract

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5
Q

What is the route of electrical activity of the heart?

A 
SA node
AV node
Bundle of His
Bundle branches
Purkinje fibres
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6
Q

What regulates calcium concentration in the cytoplasm?

A

Ryanodine receptors
Plasma membrane calcium L-type channels
SR calcium pump
Na/Ca exchangers

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7
Q

What are L-type voltage gated calcium channels?

A

Slow
Located in the plasma membrane
Found in close junction of SR
Requires a membrane potential greater than 30mV for activation
Essential for initiation and regulation of EC coupling
Smooth muscle depolarising opens them
Rapid influx of Ca2+

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8
Q

What are ryanodine receptors?

A

Mediate the release of calcium ions from the SR
Essential in contraction
Regulated by protein-protein interactions with the L type channel

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9
Q

What is the Na/Ca exchanger?

A

Plasma membrane enzyme that exchanges 3 moles of Na for 1 mole of Ca

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10
Q

What is the sarcoplasmic reticulum?

A

Organelle
Membrane bound system
Encases each myofibril within a muscle cell
Contains calcium pump

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11
Q

What is the SERCA pump?

A

Sarcoendoplasmic reticulum Ca-ATPase pump
Resides in the SR plasma membrane
Couple to ATP hydrolysis to transport calcium from cytosolic to luminal space

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12
Q

What is phospholamban?

A

Major phosphoprotein component of the SR
Help regulate SR Ca2+ uptake
Phosphorylation of phospholamban activates it

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13
Q

Describe phosphorylation of phospholamban

A

Can be phosphorylated at 3 different sites
Serine 10 by protein kinase C
Serine 16 by protein kinase A
Threonine 17 by calcium calmodulin dependent protein kinase

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14
Q

When is phospholamban active and inactive?

A

Dephosphorylated version is an inhibitor of the SERCA pump

Phosphorylated form dissociates from SERCA and activates the calcium pump

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15
Q

What links excitation and contraction?

A

Increased cytosolic Ca2+

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16
Q

What increases Ca2+ levels in the ventricular action potential?

A

Ca2+ influx through L-type Ca2+ channels in the sarcolemma

17
Q

What stimulates ryanodine receptors?

A

“Trigger calcium”

18
Q

What do ryanodine receptors do?

A

Release stored Ca2+ from the SR

19
Q

What is the first step of the cardiac contraction cycle?

A

Cardiac myocyte contraction begins with hydrolysis of ATP to ADP by myosin

20
Q

What is the second step of the cardiac contraction cycle?

A

Ca2+ released from the SR binds to TN-C

Conformational change with tropomyosin allows myosin to form an active complex with actin

21
Q

What is the third step of the cardiac contraction cycle?

A

Dissociation of ADP from myosin allows the myosin head toned

Pulls Z lines closer together and shortens the band

22
Q

What is the fourth step of the cardiac contraction cycle?

A

Binding of a new ATP molecule to myosin allows the actin-myosin complex to dissociate
Ca2+ dissociates from TN-C

23
Q

What influences cytosolic calcium concentrations?

A

Beta-adrenoreceptor coupled mechanism

24
Q

Which nervous system regulates the heart rate?

A

Autonomic

25
Q

What are chronotropic agents?

A

Factors influencing the slope of the pacemaker and therefore the heart rate

26
Q

What is the effect of sympathetic stimulation?

A

Increases cardiac muscle contractility

27
Q

What is the beta adrenergic receptor signalling pathway?

A 
Noradrenaline/adrenaline
B1 adrenergic receptor
Activation of GTP binding protein 
Stimulates adenylyl cyclase
cAMP
PKA
Phosphorylates proteins related to EC coupling
28
Q

Which two proteins together result in signal transduction?

A

Gs and Gi

29
Q

What does inotropic mean?

A

Something that increases the developed contractions

30
Q

What does lusitropic mean?

A

Something that affects cardiac relaxation

31
Q

How does the sympathetic pathway modulate calcium?

A

PKA has a lusitropic effect
Speeds up reuptake of calcium
PKA has an inotropic effect

Cardiovascular Science (12 decks)

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