General Electrophys of the Heart Flashcards
Which receptor on the nodal cell responds to the sympathetics, specifically NE? What kind of receptor is it?
ß1 receptors, it is a G(s) coupled receptor.
Which kind of G proteins stimuates adenyl cyclase? Describe this cascade.
G(s) subunit G proteins. Adenyl cyclase will turn into cAMP w/ ATP, which will stimulate PKA which will phosphorylate substrate to turn on/off things.
What is the resting potential of the nodal cell, vs the resting potential of cardiac myocytes?
-70 for nodal, -90 for cardiac myocytes.
Briefly describe phase 0, 1, 2 and 3 of the cardiac action potential.
0 is the opening of the fast gated sodium channe all the way up to 0 mVl, 1 is the overshoot into positivity, 2 is the plateau phase where Ca enters and K leaves, as well as the slow gated sodium channels, 3 is the rectifier K+ channels that causes the repolarization.
Describe the nodal cell action potential.
Looks similar to a sine wave, the upstroke is caused by slow gated calcium channels, the down stroke by rectifier K+ channels, and the “funny wave” or the “pacemaker wave” is controlled by the autonamics.
What does PKA and Phosphotase do, respectively?
PKA phosphorylates things, whereas phosphotase would dephosphorylate it.
NorEpi is released by the ANS, what is happening to the heart?
NorEpi stimulates ß1 receptors, which is a Gs receptor so adenyl cyclase turns into cAMP which activates PKA, which phosphorylates the Na, K, and Ca channels. Phosphorylation of Na and Ca opens the channels to allow cells to depolarize, but K+ phosphorylation closes them. Net result, HR increases!
For nodal cells, what ions causes it to hit depolarization? How is this achieved?
Na and Ca channels open (so they can rush into the cells), K channels closed (so they can stay IN the cell). All of this is accomplished by phosphorylation of the channels which opens the Na and Ca but closes the K.
Generally speaking how does stimulating the ß1 receptors “speed up” the heart rate?
After repolarization, there is a steeper slope to hit depolarization in the voltage vs time graph, meaning the threshold to fire is achieved faster.
What is the purpose of the “Pacemaker current” or the “funny current?”
It is to modulate the Na K and Ca channels so that we can hit depolarization faster or slower, depending.
What is the function of the Muscurinic M2 coupled receptor, what kind of G protein are they?
These are Gi proteins and their job is to do the exact opposite of Gs, thus they would inhibit adenyl cyclase so the entire cAMP to PKA to Phosphorylation pathway is blocked.
What does M2 receptors do to the heart, as opposed to the ß1? How?
M2 would slow down heart rate by doing the exact opposite of what ß1 would do: dephosphorylate Na, K and Ca channels, so now Na and Ca channels are closed, no + charge is entering the cell. The K+ channel is open, and thus K+ is leaving the cell, producing a net neg charge inside, triggering hyperpolarization and thus it will reach threshold later. As a result HR slows, bradycardia.
