Flashcards in Cardiac Cell Biology Deck (18):
Similarities between Cardiac Muscle and Skeletal Muscle
Similar contractile proteins
Mechanism of contraction is similar
Differences between Cardiac Muscle and Skeletal Muscle
1-2 Central Nuclei
More vascular, mitochondria, myoglobin, lipid droplets (Aerobic nature of cardiac muscle)
MB-Creatine Kinase (MI Marker)
What are intercalated discs?
What is their purpose?
What do transverse segments do vs lateral segments?
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
What are the excitation steps?
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)
What are the contraction steps?
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
What changes in band length when thin filaments move? (Contraction)
A-band length stays the same
I-band length shortens
What ion changes go on during relaxation?
L-type channels inactivate
Calcium is re-sequestered into SR via SERCA (Sarco-endoplasmic reticulum Calcium ATPase)
What are the histologic differences in the following regions?
Atria, SA, AV nodes
Bundle of His
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
Where does the heartbeat originate?
What regulates the heartbeat?
Intrinsic heartbeat in the myocardium
Vagus and autonomic nerves regulate heartbeat
What is the chronology of a heart attack?
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
Can heart muscle regenerate?
Natural heart regeneration is at a rate too low to restore effective function.
Can skeletal myoblasts (i.e. skeletal muscle stem cells) re-muscularize the injured heart?
Satellite cells, do not really exist in heart
Contractile improvement but leads to arrhythmia
Are cardiac fibroblasts endogenous CM stem cells?
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
Can existing monocytes mobilize to fix damaged myocardium?
How is adult cardiomyocyte proliferation induced?
Induced by inhibiting p38 MAP kinase and pro-proliferative agents (neuregulin)
Possibly inhibition of tumor supressors
Can adult stem cells in the heart fix damaged heart?
What is the marker of adult stem cells?
Where might they exist?
Obviously not, but maybe they could be mobilized to do so.
Existence is controversial however likely reside in niches
Can c-Kit+ adult stem cells be transplanted to fix injured myocardium?
Isolated and expanded c-Kit cells restored function and reduced the infarcted area
Do transplanted bone marrow cells fix injured myocardium?
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