HRR: Myocyte Action Potential Flashcards
What is an inward current?
Flow of cations from outside to inside the cell or flow of anions from inside to outside the cell
Inward current is crucial for depolarization in action potentials.
What is an outward current?
Flow of cations from inside the cell to outside the cell or flow of anions from outside the cell to inside the cell
Outward currents are important for repolarization.
Describe the three states of ion channel cycling.
- Closed: resting state, ready for activation
- Open: activated, allowing ion flow
- Inactive: cannot be activated, cycling back to closed is time-dependent
Understanding these states is essential for grasping how ion channels function in action potentials.
What is the basic structure of voltage-gated ion channels?
They have a pore, an ion filter/gate, one or more subunits, and phosphorylation sites
This structure allows for selective ion permeability crucial for action potentials.
What is a unique feature of action potential in cardiac muscle?
Hyperpolarization doesn’t happen; it just returns to resting
This characteristic differentiates cardiac action potentials from those in neurons.
Is an action potential longer or shorter in working cardiac myocytes compared to neurons?
Longer
The prolonged action potential in cardiac myocytes is essential for coordinated contractions.
What happens in phase 0 of an action potential?
Rapid upstroke in charge
This phase is critical for the initiation of the action potential.
What happens in phase 1 of an action potential?
Early repolarization
This phase marks the initial return towards resting potential.
What happens in phase 2 of an action potential?
Plateau
The plateau phase is important for sustaining the action potential in cardiac muscle.
What happens in phase 3 of an action potential?
Repolarization
This phase restores the membrane potential after depolarization.
What happens in phase 4 of an action potential?
Return to resting membrane potential
Phase 4 prepares the cell for the next action potential.
What is the inward rectifier current (IK1)?
It stabilizes membrane potential; it rectifies itself as needed
IK1 is crucial for maintaining the resting membrane potential in cardiac myocytes.
What is a typical membrane potential?
Negative 80-90 mV
This range indicates the resting state of most neurons and myocytes.
What is the significance of potassium leak channels?
They help maintain membrane potential; they do not require energy
Potassium leak channels are vital for regulating potassium ion movement across the membrane.
Where is potassium found in relation to the cell?
Inside the cell
Where is sodium found in relation to the cell?
Outside the cell
If sodium equilibrated across the membrane, what would the resting membrane potential (RMP) be?
+64
If calcium equilibrated across the membrane, what would the RMP be?
+128
If chloride equilibrated across the membrane, what would the RMP be?
-80
What ion is the biggest driver of RMP and why?
Potassium; it has a permeability of 1 due to open channels, while other ions have a permeability of 0
What happens to the membrane potential when more potassium is added outside the cell?
It causes a depolarization of the cell and raised membrane potential
What effect does adding more potassium outside of the cell have on an action potential?
It diminishes it; the amplitude and duration decrease
Describe phase 0 of the action potential.
A rapid upstroke in membrane potential due to fast sodium channels
What begins to happen toward the end of phase 0?
Chloride channels start to open, leading to the closing of sodium channels
Describe phase 1 of the action potential.
Early repolarization; potassium leaves the cell and calcium channels begin opening
What is the role of potassium channels in phase 1?
One is calcium independent and the other is calcium dependent
Describe phase 2 of the action potential.
L-type calcium channels are fully activated; slow and rapid potassium channels activate to provide a plateau
What role does the sodium-calcium exchanger play in phase 2?
It plays a small role
Describe phase 3 of the action potential.
Calcium channels are inactivated, and potassium channels are activated, allowing repolarization
What is the shape of phase 4 in cardiac myocytes?
It is flat; if not, this indicates potential for arrhythmia
What is an effective refractory period?
Another action potential cannot happen due to inactivation of sodium channels
What is a relative refractory period?
A period during which a super stimulus could trigger another action potential because some sodium channels are in the closed state.
In which phase does a delayed after depolarization occur?
Phase 4
It is caused by spontaneous calcium release from the sarcoplasmic reticulum (SR).
In which phase does early afterdepolarization occur?
Phase 2/3
It is caused by sodium and calcium channels or the sodium-calcium exchanger.
