Basic Electrophysiology Flashcards
Internal concentration of ions in cardiac myocyte
Na+:
K+:
Cl-:
Ca++:
Na+: 15mM
K+: 150mM
Cl-: 5mM
Ca++: 10-7mM
External concentrations of ions in cardiac myocyte
Na+:
K+:
Cl-:
Ca++:
Na+: 145mM
K+: 5mM
Cl-: 120mM
Ca++: 2mM
What is responsible for the zero phase (upstroke) of the action potential in nonpacemaker cells?
Sodium entry through the sodium channel
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?
Phase 2
Potassium exits through a potassium channel to repolarize the cell during phase __ of the AP
3
What exchanger channel helps maintain the low intracellular calcium concentration during resting potential?
Sodium-calcium exchanger
What pump maintains the concentration gradients for ions?
Sodium-potassium ATPase pump
What is the “funny channel”?
When is it activated?
What ions are involved and in which direction do they flow?
The funny channel is the HCN (Hyperpolarization-activated cyclic nucleotide-gated) pacemaker current
Activated during hyperpolarization
Sodium and potassium flow into the cell
How many domains do ion channels have? How many membrane spanning sections?
4; 6
Which subunit of the ion channels senses change in voltage?
S4
What is the function of the selectivity filter on ion channels?
The selectivity filter determines the ion that can pass through the channel
In the sodium channel, the loop connecting domains III and IV serves ats the channel’s ______ ____
Inactivation gate
On what side of the ion channel is the selectivity filter?
On what side of the ion channel is the inactivation gate?
Selectivity Filter = extracellular opening of channel
Inactivation gate = cytosolic side of channel
What is the function of the inactivation gate?
Another level of regulation (an intermediate state between open and closed)
In the resting state which part of the ion channel is still open? Why doesn’t this allow Na+ ions to pass through?
Inactivation gate is still open; Na+ ions cannot easily pass through because the activation gate is still closed
Which gate of the ion channel closes first after depolarization?
The inactivation gate - putting the cell in to an inactive state
Resting membrane potential of the cardiac cell lies closest to which ions membrane potential? Why?
Potassium; this is because unlike for sodium and calcium, potassium channels are open at rest
What is the equilibrium potential of potassium? Sodium? Calcium?
Potassium: -91 mV
Sodium: +70
Calcium: +130
Sodium channels rapidly inactivate in phase ___ of the action potential and are not recruited again until after phase ___
1;4
The resting potential is represented by phase __ of the AP. What current is this phase associated with?
4; inward rectifying potassium current
What contributes to the plateau phase of the action potential (phase 2)?
Slow calcium influx (and relatively low potassium efflux)
The final rapid repolarization in phase 3 largely results from what?
K+ efflux
Calcium current is primarily through what channels?
L-type calcium channels
What induces Calcium release to initate contraction?
Calcium entry
What two currents underlie influx of Potassium?
IKR a rapid component and IKS a slow component - IK slowly activates but does not inactivate
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?
Acetylcholine binding to muscarinic receptors
What is the primary intrinsic pacemaker?
SA node - spontaneous depolarization leads to action potential generation
What are the electrical synapeses connecting cardiac myocytes permitting flow of intracellular current from cell to cell?
Gap junctions
His-Purkinje fibers originate at ____ ______ and split to form _____ and _______
AV node; LBB (Left bundle branch) and RBB (Right bundle branch)
What are differences between slow-nodal and fast non-nodal cardiac action potentials?
Structures associated with each?
RMP for each?
Upstroke velocity?
- 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
What may explain the relatively slow time course and automaticity of AP in pacemaker cells?
Absence of Na+ channels and presence of spontaneously opening slow Ca++ channels
Function of ACh released from vagus nerve onto SA and AV node?
ACH decrease “funny current” in SA node reducing steepness of phase 4
Increases K+ conductance making the diastolic potential more negative
Slows conduction velocity
What is the function of norepinephrine released from sympathetic nerves
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)
What is the difference between the absolute RP (refractory period), effective RP and relative RP?
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
Steepness of phase 0 indicates….
Less negative RP results in…
Speed of depolarization
Slower rise of phase 0 and lower maximum amplitude of the action potential
What are some changes assoacated with factors that influence action potential
Temperature:
Electrolyte Imbalance:
Hyperkalemia:
Hypokalemia:
Hypercalcemia:
Hypocalcemia:
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)
Actions associated with…
P-wave:
QRS complex:
T wave:
PR:
QT:
P-wave: atrial depolarization
QRS complex: ventricular depolarization
T wave: Ventricular repolarization
PR: AV node conduction
QT: Ventricular depolarization and repolarization
Functions of Beta Blockers (block NE from sympathetic nerve)
- Prevent calcium entry into cell
- Decrease HR, conduction velocity, strength of contraction
- Used to treat CVS conditions (hypertension, MI, Arrhythmias)
Calcium Channel blockers used for…
Angina
Hypertension
Arrhythmias
*decrease entry of calcium and delay the depolarization of SA and AV nodal cells
