Flashcards in ion channels Deck (29):
1
electrical activity of the heart
1. Varies between Regions
2. Generates repetitive firing in pacemaker regions
3. Propagates within myocardium and via specialized conductive pathways
4. Trigger for contraction
5. Can Malfunction (AV block, Arrhythmias)
6. Measured via EKG (aka ECG)
2
Heart rate controlled by:
pacemaker cells in the sinoatrial node (SA node)
3
SA nodal cells fire
intrinsically at ~100/min. Rate modulated by ANS.
4
SA nodal cell rate is modulated by
ANS
5
Parasympathetic tone effect on rate?
slows rate to 60-80/min.
6
atrioventricular node (AV node) cell activity?
spontaneous activity.
but fire at lower frequency than SA nodal cells
7
AV cells are normally driven by?
This is called?
action potentials originating in the SA node (overdrive suppression).
8
Under abnormal circumstances, AV cells can?
take over initiation of the heartbeat, becoming ectopic pacemakers
9
Pumping of the heart depends upon propagation of the
action potential from the SA node to other regions.
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where does SA node propagation occur?
both within the myocardium and via specialized conducting pathways.
11
cell to cell propagation occurs via
gap junctions
12
The direction of propagation is controlled by
gap junction position and by connective tissue “insulation” (e.g., between the atria and ventricles).
13
where is the only place where action potentials can propagate from the SA node to the ventricles?
The atrioventricular node (AV node)
14
Cardiac APs categories
fast and slow.
They vary by region
15
slow regions
1. SA node
2. AV node
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fast regions
1. atrial muscle (R and L)
2. ventricular muscle (R and L)
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ion channel: direction of current flow depends on
1. membrane potential (Vm)
2. ion gradient (Nernst Potential, Eion)
18
If Vm
into cell
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If Vm>Eion, current flows
out of cell
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Current flowing into cell will cause
depolarization
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Current flowing out of cell will cause
hyperpolarization
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Ena is
+58
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Eca is
+124
24
Ek is
-90
25
Sodium current
1. (INa) – (NaV1.5)
2. Voltage-dependent inactivation
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Calcium currents:
1. ICa-L
2. ICa-T
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ICa-L
1. L-type current;
2. dihydropyridine receptor,
3. DHPR (CaV1.2, CaV1.3)
4. High Voltage Activated (HVA)
5. Both voltage- and calcium-dependent inactivation
28
ICa-T
1. T-type current
2. (CaV3.1, CaV3.2)
3. Low-Voltage Activated (LVA)
4. Voltage-dependent Inactivation
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