Cardiac Cell Biology Flashcards

1
Q

Similarities between Cardiac Muscle and Skeletal Muscle

A

Basal lamina
Striated
Similar contractile proteins
Mechanism of contraction is similar

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2
Q

Differences between Cardiac Muscle and Skeletal Muscle

A
Involuntary
Myocytes
1-2 Central Nuclei
Myocytes
More vascular, mitochondria, myoglobin, lipid droplets (Aerobic nature of cardiac muscle)
MB-Creatine Kinase (MI Marker)
Intercalated discs
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3
Q

What are intercalated discs?
What is their purpose?
What do transverse segments do vs lateral segments?

A

Structure: Sarcolemma specializations between adjoining cells
Purpose: Enable cardiac myocytes to work as a unit as if they were in a syncytium
Transverse segments: Transmit force, modified Z-band, made up of fascia adherens (N-cadherins) & desmosomes
Lateral segments: Cell-cell signaling made up of gap junctions (nexus) & some desmosomes

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4
Q

What are the excitation steps?

A

Action potential depolarization in the T-tubules
Phase 2 of the AP due to the L-type Ca 1.2 resulting in calcium influx
Calcium triggers ryanodine receptors in the SR: Resulting in more Ca release (CICR)

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5
Q

What are the contraction steps?

A

Calcium binds to troponin-C to cause tropomyosin to move
Myosin head is activated by ATP hydrolysis & binds to actin
Power stroke = contraction: Myosin pulls actin into the A-band & the sacromere shortens

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6
Q

What changes in band length when thin filaments move? (Contraction)

A

During contraction:
A-band length stays the same
I-band length shortens

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7
Q

What ion changes go on during relaxation?

A

L-type channels inactivate

Calcium is re-sequestered into SR via SERCA (Sarco-endoplasmic reticulum Calcium ATPase)

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8
Q
What are the histologic differences in the following regions?
Atria, SA, AV nodes
Bundle of His 
Endocardium
Cardiac fibroblasts
A

Atria, SA, AV nodes - Smaller myocytes with fewer striations; Atrial membrane-bound granules contain atrial natriuretic factor (ANF or ANP)
Bundle of His - contains Purkinje myocytes (conduction specialized cardiac myocyte)
Endocardium - Single layer of endothelial cells
Cardiac fibroblasts - Most abundant cell type but myocytes are larger and comprise most of the heart volume

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9
Q

Where does the heartbeat originate?

What regulates the heartbeat?

A

Intrinsic heartbeat in the myocardium

Vagus and autonomic nerves regulate heartbeat

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10
Q

What is the chronology of a heart attack?

A

Immediate: Myocyte death resulting in MB-CK & cTnl release
15 hours: Inflammation
2-3 days: Wound healing via cardiac fibroblasts, yielding fibrosis
2-4 days: Angiogenesis which can be clinically enhanced by VEGF and FGF possibly
Scar deposition due to collagen cross-linking

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11
Q

Can heart muscle regenerate?

A

Yes, maybe.

Natural heart regeneration is at a rate too low to restore effective function.

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12
Q

Can skeletal myoblasts (i.e. skeletal muscle stem cells) re-muscularize the injured heart?

A

Satellite cells, do not really exist in heart

Contractile improvement but leads to arrhythmia

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13
Q

Are cardiac fibroblasts endogenous CM stem cells?

A

No: At least 1 CF borders each CM but fibroblasts can not regenerate heart.
Fibroblasts respond to injury by making a permanent, non-contractile scar.
But as of 2012 CFs may be induced into CMS

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14
Q

Can existing monocytes mobilize to fix damaged myocardium?

How is adult cardiomyocyte proliferation induced?

A

Maybe.
Induced by inhibiting p38 MAP kinase and pro-proliferative agents (neuregulin)
Possibly inhibition of tumor supressors

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15
Q

Can adult stem cells in the heart fix damaged heart?
What is the marker of adult stem cells?
Where might they exist?

A

Obviously not, but maybe they could be mobilized to do so.
c-Kit marker
Existence is controversial however likely reside in niches

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16
Q

Can c-Kit+ adult stem cells be transplanted to fix injured myocardium?

A

Isolated and expanded c-Kit cells restored function and reduced the infarcted area

17
Q

Do transplanted bone marrow cells fix injured myocardium?

A

Some evidence for bone marrow cell migration to the heart and staying there as adult stem cells: Transplanted hearts can be invaded by host immune system
Animal studies revealed little or no re-muscularization

18
Q

Is transplanting iPSCs feasible?

A

Cardiomyocytes can definitely be generated from iPSCs.