Test 1: Wk2: 4 Cardiac Electrophysiology - Puri Flashcards
at rest the cardiac myocyte is only permeable to
K+
at rest the cardiac RMP =
Nernst potential for K+
potential is reliant upon — concentration inside and outside the cell
K+
depol — probability of both open and inactive channels
increases
repolarization induces recovery from — to —
inactive to closed
the number of cation channels available for the next cycle and there readiness depends on
RMP
Outward rectifiers
open as the membrane depolarizes, K+ rapidly repolarizes the cell
Inward rectifiers
open at rest and allow K+ to leave cell when Vm
what direction does K+ always go in
leaves the cell
phase 0
rapid upstroke - depol of cardiac muscles
phase 1
initial repolarization
phase 2
stabilization of membrane potential - plateau phase
refractory period
duration of phase 2
phase 3
rapid repolarization
phase 4
return to resting membrane potential
phase 0 ions
Na in
K x
phase 1 ions
K out
phase 2 ions
Ca in
K out
phase 3 ions
Ca x
K out
phase 4 ions
K open but no outward movement of K when equilibrium is reached
Na/ATPase restores balance
— drive repolarization and remain open from phase — to —
outward rectifiers
1 3
— close as the Vm approaches 0 and the action potential is made possible
inward rectifiers
— sodium channels are the main targets of antiarrhythmic drugs
SCN5A
Na channels open when mV =
-70
Na channels have —
time dependent inactivation
reactivation of Na channels requires almost complete — of Vm
repolarization
— Ca channels are critical for — cardiac contraction
L type
initiating
— open slowly as the membrane depol and remain open until — mV
delayed outward rectifiers
-70
— open when mV reaches — and remain open at rest
inward rectifiers
-60
absolute refractory period
inactivation of fast Na channels
relative refractory period -
the action potential has
some Na channels recover to closed state and cane be activated at higher than normal threshold
reduced conduction velocity
Supernormality
the action potential is
threshold for activation is lower than resting cardiac myocyte
still slow
the duration of refractoriness depend on the — and — of the repolarizing current via —
strength and rapidity
K+
outward rectifiers
P wave represents
atrial deopl
QRS complex is produced by
the summed up phase 0 ventricular myocytes action potentials
QRS complex is wider when
velocity is decrease
ST segment corresponds to
the plateaus of the action potentials
ST segment is dependent on balance of
incoming Ca and outgoing K
T wave is produced by
ventricular repol
T wave depends on
strength of outward K current
QT interval is the
action potential duration
TP segment is phase — of the —
phase 4 of fast action potential
many antiarrhythmic drugs target
fast Na channels
lidocaine
delay recovery of fast Na channels from inactivation at -65
SCN5A recover at -80
quinidine, amiodarone
prevent or delay SCN5A opening - slowing upstroke of fast action potential
amiodarone
interrupt cardiac rythym
prolong the ERP - K+ channel blockers
verapamil
Ca channel blocker
reduce strength of cardiac contraction -0 shorten ERP
action potential in the nodes have no
phase 1 or 2
Nodes phase 0
opening of L Ca channels ➡ Ca mediated inward current
Nodes Phase 3
Kr and Ks channels open ➡ mediated inward current
Nodes resting membrane potential
less negative - fewer K open
phase 4 autonomic depol
funny current
what is the natural pacemaker of the heart, why
SA node
highest density of HCN channels
HCN channel order of density
SA > AV > His-Purkinje
SNS Control of HR
beta adrenergic stimulation increases Gas and increases cAMP and PKA
SNS Control of HR
increases HCN activity ➡
⬆ slope of phase 4 depol
SNS Control of HR
lower threshold for opening of
L Ca channels
SNS Control of HR
faster opening of L Ca channels ➡
⬆ slope of phase 0
SNS Control of HR
faster repol vie increased Ik currents ➡
⬆ slope of phase 3
PNS Control of HR
PNS stimulation activates — and reduces — ➡ ⬇ — phosphorylation ➡ —
Gi
cAMP
HCN
slower phase 4 depol
PNS Control of HR
↓ — → ↓ — phosphorylation → higher threshold for — channel opening
and —
↓ cAMP → ↓ L-type phosphorylation → higher threshold for Ca++ channel opening
and slower phase 0 depolarization
PNS Control of HR
Stimulation of — rectifiers — the resting membrane Vm
Stimulation of KAch inward rectifiers lowers the resting membrane Vm
– tone is the predominant tone regulation resting HR
parasympathetic
Automatic phase —depolarization of the SA node predominate, and spread to the left atria via the —
Automatic phase 4 depolarization of the SA node predominate, and spread to the left atria via the Bachman’s bundle
— is the first to depolarize
Right atria is the first to depolarize → depolarization
spread from right to left, and downwards towards the
AV node–this is sinus rhythm
— nodes depolarizes the bundle of His which divides
into — in the septum
AV nodes depolarizes the bundle of His which divides
into left and right branches in the septum
depolarization in the septum spreads from — to —
depolarization in the septum spreads from left to right
— terminate in Purkinje fibers, which
make contacts with myocardial cells
Bundle branches terminate in Purkinje fibers, which
make contacts with myocardial cells
Depolarization spreads across the — by
myocardial cell-to-cell conduction
Depolarization spreads across the ventricles by
myocardial cell-to-cell conduction → spread across
ventricles is more or less uniform
— facilitate cell-cell transmission of the cardiac —
Gap junctions facilitate cell-cell transmission of the cardiac action potential
structure or gap junctions
formed by the interaction of the connexons of two neighboring cells
Connexon
composed of six membrane-spanning proteins (connexins) with a central pore
In cardiomyocytes
connexons control
control the passage of electrical stimulus
The impulse from the — node depolarizes the resting cardiac myocyte
The impulse from the SA node depolarizes the resting cardiac myocyte
How does the electrical
impulse propagate?
see slide
current sink
Positive charges from the membrane ahead of the
action potential flow into the area of negative charge
represented by the action potential
what causes current sink
due to the flow of electrons on
either side of the membrane
Speed of impulse propagation is termed
conduction velocity
— have the slowest conduction
velocity in the heart
Nodes have the slowest conduction
velocity in the heart
Na/Ca exchanger is
bidirectional
Na/Ca exchanger # Na exchanged for # Ca
3 Na for 1 Ca
