Basic Electrophysiology

Question 1

Internal concentration of ions in cardiac myocyte

Na⁺:

K⁺:

Cl^-:

Ca⁺⁺:

Answer 1

Na⁺: 15mM

K⁺: 150mM

Cl^-: 5mM

Ca⁺⁺: 10^-7mM

Question 2

External concentrations of ions in cardiac myocyte

Na⁺:

K⁺:

Cl^-:

Ca⁺⁺:

Answer 2

Na⁺: 145mM

K⁺: 5mM

Cl^-: 120mM

Ca⁺⁺: 2mM

Question 3

What is responsible for the zero phase (upstroke) of the action potential in nonpacemaker cells?

Answer 3

Sodium entry through the sodium channel

Question 4

At what phase of the Purkinje fiber and muscle cell action potential does calcium enter the cell through calcium channels causing depolarization of pacemaker cells?

Answer 4

Phase 2

Question 5

Potassium exits through a potassium channel to repolarize the cell during phase __ of the AP

Answer 5

3

Question 6

What exchanger channel helps maintain the low intracellular calcium concentration during resting potential?

Answer 6

Sodium-calcium exchanger

Question 7

What pump maintains the concentration gradients for ions?

Answer 7

Sodium-potassium ATPase pump

Question 8

What is the “funny channel”?

When is it activated?

What ions are involved and in which direction do they flow?

Answer 8

The funny channel is the HCN (Hyperpolarization-activated cyclic nucleotide-gated) pacemaker current

Activated during hyperpolarization

Sodium and potassium flow into the cell

Question 9

How many domains do ion channels have? How many membrane spanning sections?

Answer 9

4; 6

Question 10

Which subunit of the ion channels senses change in voltage?

Answer 10

S4

Question 11

What is the function of the selectivity filter on ion channels?

Answer 11

The selectivity filter determines the ion that can pass through the channel

Question 12

In the sodium channel, the loop connecting domains III and IV serves ats the channel’s ______ ____

Answer 12

Inactivation gate

Question 13

On what side of the ion channel is the selectivity filter?

On what side of the ion channel is the inactivation gate?

Answer 13

Selectivity Filter = extracellular opening of channel

Inactivation gate = cytosolic side of channel

Question 14

What is the function of the inactivation gate?

Answer 14

Another level of regulation (an intermediate state between open and closed)

Question 15

In the resting state which part of the ion channel is still open? Why doesn’t this allow Na+ ions to pass through?

Answer 15

Inactivation gate is still open; Na+ ions cannot easily pass through because the activation gate is still closed

Question 16

Which gate of the ion channel closes first after depolarization?

Answer 16

The inactivation gate - putting the cell in to an inactive state

Question 17

Resting membrane potential of the cardiac cell lies closest to which ions membrane potential? Why?

Answer 17

Potassium; this is because unlike for sodium and calcium, potassium channels are open at rest

Question 18

What is the equilibrium potential of potassium? Sodium? Calcium?

Answer 18

Potassium: -91 mV

Sodium: +70

Calcium: +130

Question 19

Sodium channels rapidly inactivate in phase ___ of the action potential and are not recruited again until after phase ___

Answer 19

1;4

Question 20

The resting potential is represented by phase __ of the AP. What current is this phase associated with?

Answer 20

4; inward rectifying potassium current

Question 21

What contributes to the plateau phase of the action potential (phase 2)?

Answer 21

Slow calcium influx (and relatively low potassium efflux)

Question 22

The final rapid repolarization in phase 3 largely results from what?

Answer 22

K+ efflux

Question 23

Calcium current is primarily through what channels?

Answer 23

L-type calcium channels

Question 24

What induces Calcium release to initate contraction?

Answer 24

Calcium entry

Question 25

What two currents underlie influx of Potassium?

Answer 25

I_KR a rapid component and I_KS a slow component - I_K slowly activates but does not inactivate

Question 26

What regulates G-protein activated K+ current in SA and AV nodal cells that decrease pacemaker rate and slow conduction rate through the AV node?

Answer 26

Acetylcholine binding to muscarinic receptors

Question 27

What is the primary intrinsic pacemaker?

Answer 27

SA node - spontaneous depolarization leads to action potential generation

Question 28

What are the electrical synapeses connecting cardiac myocytes permitting flow of intracellular current from cell to cell?

Answer 28

Gap junctions

Question 29

His-Purkinje fibers originate at ____ \_\_\_\_\_\_ and split to form _____ and \_\_\_\_\_\_\_

Answer 29

AV node; LBB (Left bundle branch) and RBB (Right bundle branch)

Question 30

What are differences between slow-nodal and fast non-nodal cardiac action potentials? ## Footnote Structures associated with each? RMP for each? Upstroke velocity?

Answer 30

* Structures associated with each? * Slow - SA and AV nodal cells * Fast - Atrial, ventricular muscle cells and Purkinje fibers * RMP for each? * Slow: -40 to -70 mV * Fast: -80 to -90 mV * Upstroke velocity? * Slow: 1-10V/sec * Fast: \>100/500V/sec

Question 31

What may explain the relatively slow time course and automaticity of AP in pacemaker cells?

Answer 31

Absence of Na+ channels and presence of spontaneously opening slow Ca++ channels

Question 32

Function of ACh released from vagus nerve onto SA and AV node?

Answer 32

ACH decrease "funny current" in SA node reducing steepness of phase 4 Increases K+ conductance making the diastolic potential more negative Slows conduction velocity

Question 33

What is the function of norepinephrine released from sympathetic nerves

Answer 33

Acts on ß-adrenergic receptors in SA and AV nodes Increases "funny channel" and steepness of phase 4 Makes threshold more negative Does not effect maximum diastolic potential Increases Calcium influx, stimulate SERCA (increasing stores of calcium for release)

Question 34

What is the difference between the absolute RP (refractory period), effective RP and relative RP?

Answer 34

During absolute RP the cell is unexcitable to stimulation The effective RP is a brief time beyond the absolute RP during which stimulation produces a localized depolarization that does not propagate During the relative RP stimulation produces a weak action potential that propagates, but more slowly than usual curve

Question 35

Steepness of phase 0 indicates.... Less negative RP results in...

Answer 35

Speed of depolarization Slower rise of phase 0 and lower maximum amplitude of the action potential

Question 36

What are some changes assoacated with factors that influence action potential Temperature: Electrolyte Imbalance: Hyperkalemia: Hypokalemia: Hypercalcemia: Hypocalcemia:

Answer 36

Temperature - increase in body temp increases SA node firing Electrolyte imbalance - Imbalance of K+ and Ca++ can have serious effects Hyperkalemia - Raises the resting potential; slows conduction - reduction of P wave amplitude Hypokalemia - Decrease in resting potential - flattening of T wave Hypocalcemia and Hypercalcemia - alter myocardial AP duration (Hyper shortens ST segment and QT interval; Hypo prolongs)

Question 37

Actions associated with... ## Footnote P-wave: QRS complex: T wave: PR: QT:

Answer 37

P-wave: atrial depolarization QRS complex: ventricular depolarization T wave: Ventricular repolarization PR: AV node conduction QT: Ventricular depolarization and repolarization

Question 38

Functions of Beta Blockers (block NE from sympathetic nerve)

Answer 38

* Prevent calcium entry into cell * Decrease HR, conduction velocity, strength of contraction * Used to treat CVS conditions (hypertension, MI, Arrhythmias)

Question 39

Calcium Channel blockers used for...

Answer 39

Angina Hypertension Arrhythmias \*decrease entry of calcium and delay the depolarization of SA and AV nodal cells