Lecture 6 - Cardiac Excitation Contraction Coupling

Question 1

Where are the ca2+ ions stored?

Answer 1

In the SR (sarcoplasmic recticulum)

Question 2

What is the ventricular myocyte?

Answer 2

A Muscle cell in the ventricle

Question 3

What are some types of ON mechanisms?

Answer 3

VOC (voltage operated calcium channels) and RYR (ryanodine receptors)

Question 4

What type of RYR is found in the muscle cell?

Answer 4

Type 2 RYR

Question 5

What happens when the VOC is activated?

Answer 5

Ca2+ ions come into the cell down the concentration gradient, these ca2+ ions s provide the trigger ca2+ for CICR in the RYR

Question 6

What happens when ca2+ is released into the SR?

Answer 6

The trigger ca2+ that produces CICR in the RYR triggers contraction

Question 7

What are the types of OFF mechanism?

Answer 7

PMCA, SERCA pump and NA+,Ca2+ exchanger, Na,K+ ATPase pump

Question 8

What does the PMCA pump do?

Answer 8

Pumps ca2+ out of the cell and brings down the ca2+ ions once the cell has stopped being stimulated

Question 9

What does the SERCA pump do?

Answer 9

Pumps ca2+ ions back into the SR so the SR can refill for the next stimulation

Question 10

What does the Na+ ca2+ exchanger do in the membrane?

Answer 10

Removes ca2+ ions from the cytoplasm and replaces them with Na+ - you need an inwards Na+ gradient for this to work

Question 11

What does the Na+ K+ ATPase pump do?

Answer 11

Ensures the outside has plenty of Na+ ions and that ensures that inside has plenty of k+ ions.

Question 12

How do you activated the VOC?

Answer 12

Need to have NaVOC which activates the CaVOC

Question 13

What needs to happen after depolarisation?

Answer 13

There needs to be repolarisation and this happens by the KVOC

Question 14

What do both on and off mechanisms have?

Answer 14

Beta 1 receptors to regulate the cell they are coupled to GS and Adenylyl cyclase

Question 15

What does cyclic AMP activate?

Answer 15

Protein kinase A

Question 16

What does protein kinase A phosphorylate?

Answer 16

Phosphorylates and activates CaVOC and the RYR and speeds up the SERCA pump

Question 17

What protein does PKA affect?

Answer 17

Phospholamban which is the regulatory protein of SERCA pump

Question 18

What does the shape of the action potential in heart depend on?

Answer 18

It depends on where it is in the heart tissue - shape depends on the function

Question 19

What are the 3 different types of action potential in the heart?

Answer 19

A ventricular muscle cell, atrial muscle cell and Sino atrial node

Question 20

How does the action potential in the SA node get to the AV node when depolarised? - spread of excitation in the heart

Answer 20

By intermodal pathways

Question 21

What happens once the action potential reaches the AV node?

Answer 21

The action potential stays there for a while because the depolarisation from the SA node spreads more slowly across the atrial muscle

Question 22

How does depolarisation move through ventricular muscle?

Answer 22

Moves rapidly through the ventricular conducting system to the apex of the heart, the depolarisation spreads upwards from the apex and this depolarises the ventricles

Question 23

What are membrane potential auto rhythmic cells used for?

Answer 23

SA node can set its own rate of depolarisation, can depolarise at its own frequency and this frequency sets the heart beat

Question 24

What is the SA node known as?

Answer 24

The pacemaker of the heart - it constantly fires action potentials to the heart

Question 25

On a cardiac action potential - what is phase 0?

Answer 25

Rapid depolarisation (inward Na current)

Question 26

What is phase 1?

Answer 26

Overshoot

Question 27

What is phase 2?

Answer 27

Plateau (inward ca2+ current) - the trigger ca2+

Question 28

What is phase 3?

Answer 28

Repolarisation (outward K+ Current)

Question 29

What is phase 4?

Answer 29

Resting potential

Question 30

What is different in the action potentials of neuronal and muscle action potential?

Answer 30

Phase 2 is different - phase 2 is longer in muscle than neuronal as it represents the trigger ca2+ entering the cell to trigger CICR to get RYR to form a contraction

Question 31

What does a long refractory period prevent?

Answer 31

Tetany

Question 32

In atrial cells why is phase 2 less pronounced? (Smaller)

Answer 32

They don’t have as much as ca2+ as they do not need to pump blood all around the body so just have to pump to the ventricles

Question 33

What is the resting membrane potential of the SA node?

Answer 33

It is -55, a much slower response