Cardiac Muscle: Excitation and Signaling Flashcards
Review: To which ion are cells most permeable? And this, to which ion’s Nernst equilbrium potential is the cell’s resting potential closest?
K+
5 phases of the action potential?
4: Resting.
0: Upstroke (rapid depolarization).
1: Rapid repolarization.
2: Plateau of depolarization with slow repolarization.
3: Rapid repolarization back to resting potential.
What happens if you raise extracellular K+?
The resting potential of cardiac myocytes increases, so it’s easier to depolarize.
The K+ channel has a GYG-based selectivity filter.
Good.
Review: Why do V-gated Na+ channels have refractory period of inactivity?
They have that inactivation gate with “ball and chain” which blocks up open channels.
What’s the T-type Ca++ for? How does it’s activation relate to voltage?
It’s activated at low membrane potentials (-80ish mV to -40mV) - contributing to the unstable resting potentials of SA and AV nodes.
They also have “ball and chain” inactivation gates.
How does L-type Ca++ channels’ activity relate to voltage? For what process are they important?
L-type Ca++ channels are activated at higher voltages (-40mV to 0ish mV), making them very important for maintaining the plateau of depolarization seen in some cardiac myocytes.
They also have “ball and chain” inactivation gates.
What does the delayed rectifier K+ current refer to?
When the cell is depolarized, K+ moves out of the cell to repolarize the membrane potential.
(the K+ inward rectifier current also does this… for a longer time? Not sure if there’s a less subtle difference.)
What does the transient outward current - I (TO1) - do?
After the Phase 0 upstroke, pulls the voltage down a little… giving the action potential “shape” specific to the cell type… (pretty vague)
Do SA and AV nodes use Na+ currents for depolarization?
No. They’re more about the “slow” depolarization via T-type Ca++ channels.
Do Perkinje fibers and the bundle of His use Na+ current to depolarize the cells?
Yes, their depolarization is very fast.
What’s wrong in long QT syndrome? (simple version… I’m sure we’ll hear more later)
Refractory period is too long, sometimes because K+ channels aren’t working well to repolarize. Also can be due to mutations in V-gated Na+ channels.
Which has a longer depolarization plateau: atrial or ventricular myocytes?
Ventricular myocytes have a longer depolarization plateau.
At what voltage, roughly, does Perkinje fibers’ depolarization plateau?
In the negative range… about -20mV.
How do gap junctions in cardiac myocytes know to shut when there has been injury to nearby cells?
High intracellar Ca++ causes connexons to close, preventing spread of damaging Ca++ / depolarization.
