cardiac muscle structures Flashcards
contractile cells of the heart
myocytes
The largest cell population by number is
endothelial cells, followed by cardiac fibroblasts
predominant components of the ECM are:
Fibrillar collagen type I and III
disruptions in the ECM occur with
disease and cardiac remodeling
Cardiac muscles are:
- striated
- not under direct neural control (unlike skeletal which are)
- shorter, narrower
- richer in mitochondria
- one nucleus
- Ca2+ binds to troponin, which regulates actomyosin interaction
ATPase activity of myosin is
slower in cardiac than skeletal but faster than smooth muscle
in cardiac muscle, Ca2+ binds to
troponin, which regulates actomyosin interaction
Cardiac muscle cells are connected with each other through
intercalated discs
coupling between cardiac muscle cells is
both mechanical and electrical
intercalated discs
- Coincide with the Z discs; contain desmosomes and gap junctions
- Desmosomes provide adhesion and assure that the force generated in one cell passes to the other (connects to ECM)
- Gap junctions provide low resistance pathways for electrical current
Myofibrils and mitochondria occupy about
85% of the heart cell volume (the rest contains sarcolemma, T-tubules, SR, intercalated disks, gap junctions, etc)
thick filament
composed of hundreds of long, contractile myosin molecules arranged in a staggered side by side complex
thin filament
composed of hundreds of long, contractile myosin molecules arranged in a staggered side by side complex
saracomere
unit of contractile activity composed mainly of actin and myosin and extending from Z line to Z line in a myofibril
myofibril
end to end arrays of identical sarcomeres
myofiber
a single, multinucleated muscle cell containsing all the usual cell organelles plus many myofibrils
muscle
organized array of muscle fibers
a cardiac muscle cell is made up of
sarcomeres
sarcomere is defined as
z line to z line
the a band is
thick filaments
the I band is
thin filament extensions from the Z line
major contractile protein
- myosin
2. actin
Myosin
- Composed of two heavy chains and four light chains (RLC, ELC) with a mass of about 480,000 daltons.
- Developmental regulation of isoforms (and with disease).
- HC isoform determines ATPase activity (a vs b)
Actin is
- Similar to skeletal muscle myosin
2. Binds tropomyosin and troponin
major regulatory
- troponin C
- troponin I
- troponin T
- tropomyosin
Troponin C (TN-C)
A dumbbell shaped protein with the N-lobe containing only one Ca2+-binding site (unlike skeletal which contains two)
troponin I (TN-I)
- Contains a unique N-terminal extension of 32 amino acids that contains 2 PKA phosphorylation sites critical for adrenergic responsiveness of the heart.
- This extension interacts with TN-C but is released with phosphorylation.
(KNOW THIS)
TN-C ca2+ binding sites
only one calcium binding site, compared to 2 in skeletal
Troponin T (TN-T)
- Binds tropomyosin.
2. Developmental regulation of isoform expression (and perhaps pathological regulation).
Tropomyosin
only the alpha isoform is in the heart
