Lecture 6 - Cardiac Excitation Contraction Coupling Flashcards
Where are the ca2+ ions stored?
In the SR (sarcoplasmic recticulum)
What is the ventricular myocyte?
A Muscle cell in the ventricle
What are some types of ON mechanisms?
VOC (voltage operated calcium channels) and RYR (ryanodine receptors)
What type of RYR is found in the muscle cell?
Type 2 RYR
What happens when the VOC is activated?
Ca2+ ions come into the cell down the concentration gradient, these ca2+ ions s provide the trigger ca2+ for CICR in the RYR
What happens when ca2+ is released into the SR?
The trigger ca2+ that produces CICR in the RYR triggers contraction
What are the types of OFF mechanism?
PMCA, SERCA pump and NA+,Ca2+ exchanger, Na,K+ ATPase pump
What does the PMCA pump do?
Pumps ca2+ out of the cell and brings down the ca2+ ions once the cell has stopped being stimulated
What does the SERCA pump do?
Pumps ca2+ ions back into the SR so the SR can refill for the next stimulation
What does the Na+ ca2+ exchanger do in the membrane?
Removes ca2+ ions from the cytoplasm and replaces them with Na+ - you need an inwards Na+ gradient for this to work
What does the Na+ K+ ATPase pump do?
Ensures the outside has plenty of Na+ ions and that ensures that inside has plenty of k+ ions.
How do you activated the VOC?
Need to have NaVOC which activates the CaVOC
What needs to happen after depolarisation?
There needs to be repolarisation and this happens by the KVOC
What do both on and off mechanisms have?
Beta 1 receptors to regulate the cell they are coupled to GS and Adenylyl cyclase
What does cyclic AMP activate?
Protein kinase A
What does protein kinase A phosphorylate?
Phosphorylates and activates CaVOC and the RYR and speeds up the SERCA pump
What protein does PKA affect?
Phospholamban which is the regulatory protein of SERCA pump
What does the shape of the action potential in heart depend on?
It depends on where it is in the heart tissue - shape depends on the function
What are the 3 different types of action potential in the heart?
A ventricular muscle cell, atrial muscle cell and Sino atrial node
How does the action potential in the SA node get to the AV node when depolarised? - spread of excitation in the heart
By intermodal pathways
What happens once the action potential reaches the AV node?
The action potential stays there for a while because the depolarisation from the SA node spreads more slowly across the atrial muscle
How does depolarisation move through ventricular muscle?
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
What are membrane potential auto rhythmic cells used for?
SA node can set its own rate of depolarisation, can depolarise at its own frequency and this frequency sets the heart beat
What is the SA node known as?
The pacemaker of the heart - it constantly fires action potentials to the heart
On a cardiac action potential - what is phase 0?
Rapid depolarisation (inward Na current)
What is phase 1?
Overshoot
What is phase 2?
Plateau (inward ca2+ current) - the trigger ca2+
What is phase 3?
Repolarisation (outward K+ Current)
What is phase 4?
Resting potential
What is different in the action potentials of neuronal and muscle action potential?
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
What does a long refractory period prevent?
Tetany
In atrial cells why is phase 2 less pronounced? (Smaller)
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
What is the resting membrane potential of the SA node?
It is -55, a much slower response
