Cardiac Muscle Flashcards
What are some properties unique to cardiac mm?
Cells are short, branch and interdigitate
Presence of intercalated disks
What are some properties that are common for cardiac and skeletal mm?
Striated Sarcomeres (thick, thin filaments) Same sliding filament mechanism Crossbridge cycling is similar T-tubules and SR
Cardiac muscle cells are similar to _________skeletal muscle fibers
Type I (slow oxidative)
because -depend on oxidative phosphorylation
- numerous mitochondria
- highly resistant to fatigue
- BUT highly dependent on continuous supply of O2
What are the 3 types of connections b/n cardiac myocytes?
Zonula Adherens
Macula Adherens (Desmosomes)
Gap Junction
What are the two connections that make up intercalated discs?
Macula Adherens (Desmosomes) Gap Junction
Define physical and functional coupling?
Physical coupling: points where cells mechanically pull on each other-Zonula adherens, Macula adherens (Desmosomes)
Functional coupling: allow electrical signals to pass between cells-Gap junctions
Define sliding filament mechanism of muscle contraction.
Thin filaments sliding over thick filaments causing muscle contraction.
NOTE: during muscle contraction the H and I-bands shorten. While the A-band doesn’t change.
What are the different states of crossbridge cycling?
Attached state-Released state (ATP attaches to myosin)-Cocked state (ATP is hydrolyzed, myosin at resting conformation)-Crossbridge state (myosin head binds to a new position on actin)-Power-stroke state (P is released, shortening and force development)-Attached state (ADP is released)
What are two molecules essential for crossbridge cycling?
Ca
ATP
What is the difference b/n cardiac and skeletal muscle at the membrane system for E-C (excitation-contraction) coupling?
Cardiac mm:
- more sparse SR,
- dyad-SR, TT (triad-1T-tubule b/n 2SR’s in SK mm),
- d/f T-tubule position cardiac mm @ z-line (SK mm A-I band junction), -bigger T-tubule (200 nm vs. 30 nm in SK mm)
How are cardiac mm d/f from skeletal mm in handling Ca during E-C coupling?
Skeletal mm: AP gets to the T-tubule–DHPR (on T-tubule) senses Vm–change in conformation of DHPR results in change in conformation of RyR of the SR–Voltage (depolarization)-dependent Ca release from SR to the cytosol–CONTRACTION
Cardiac mm: AP gets to the T-tubule–DHPR acts as Ca channel–[Ca] in the cytosol increases–Ca-Induced Ca Release from the SR
T/F Cardiac mm can NOT contract in the absence of extracellular Ca.
T. Unlike SK mm., Cardiac mm need CICR to generate contraction.
What is another name for DHPR in cardiac mm?
L-type Ca channel
What are the 3 ways that DHPR regulates cardiac function?
DHPR (L-type Ca channel) regulates cardiac function:
- physiologically (ex. sympathetic stimulation)
- pharmacologically (ex. calcium channel blockers)
- pathologically (ex. ischemia)
T/F Ca influx during AP must not be balanced by a Ca efflux b/n APs.
F. It must be balanced. There are different channels responsible for the entry and exit of Ca.