Cardio Myocyte Function Flashcards
Cardiac Muscle
Striated, branched, uninucleated
Involuntary
Intercalated Discs (gap junctions, desmosomes-anchor, fascia adherens- stabilize tissue)
EC coupling
excitation-contraction coupling- how an AP along the cardiomyocyte membrane induces contraction
AP duration and Contraction
cardio vs skeletal
cardiac:
duration 200 to 300 ms
contraction 300 ms
skeletal
duration 2-5 ms
contraction 75 ms
what type of muscle fiber cannot reach tetanus
cardiac
Fast Cardiac AP
0- influx of Na+ for ra[id depolarization
1,2- slow Ca2+ channels open
3- repolarization K+ and Ca2+
4- K channels closes, levels off
How contraction occurs
- AP travels to T tubule
- Voltage sensitive DHP receptors (L type Ca2+ channels) (only voltage sensitive in skeletal muscles)
- Ca2+ influx causes release from SR
- Ca2+ finds to troponin C (changes to troponin I), then cross bridge formation
- SERCE gets Ca2+ back into SR
- Na+/Ca2+ exchanger lowers intracellular Ca2+ and ends contraction
Inotropy
amount of tension a myocyte can produce at any given resting myocte and sarcomere length
fun fact: calcium released from cardiac muscle SR is usually insufficient to produce peak force, but in skeletal muscle it is always enough for peak force
What 4 factors increase Ca2+ tension
- Sympathetic activity
- Decrease sympathetic activity
- Drugs
- Increase in HR
How does sympathetic activity increase contraction?
3 ways
NE activation of B1 reception which stimulates cAMP
1) phosphorylates L type Ca2+ increase Ca2+ influx into cell
2) phosphorylates phospholamban, removing inhibition of SERCA, increasing Ca2+ reuptake into SR
3) Phosphorylates Troponin-I which enhances binding of Ca2+ to TN-C, which increases cross bridging (not Ca2+)
HR increases contraction by:
Bowditch effect
Increases frequency of AP, increases Ca2+ influx, increases SR Ca2+ release, increases contactivitity
also increasing AP frequency, increase Na+ influx, less efficient ATPase, lowers Na/Ca2+ exchange, increases cytsolic Ca2+, increases Ca2+ SR reuptake
also decreases time in diastole, increases Na and Ca, increases SR Ca stores, increases contraction
Parasympathetic effect
Inhibits SNS activity
Lowers HR
Beta Blockers
negative inotrope
inhibits B1 receptors/adrenergic effect
Digitalis (cariac glycosides
inhibits Na/K ATPase activity
low Na+ gradient, lessens Na/Ca exchanges
Increase cytosolic and SR Ca2+
Cardiac muscle and tension relationship
has greater sensitivity than skeletal muscle due to
- Increased overlap by Actin and Myosin
- Length dependent increase in calcium sensitivity of troponin C
- Stretch-activated plasma membrane calcium channels
Frank-Starling
Increases ventricular filling, increase stretch, increase tension
SV is dependent on End Diastolic Voluse
Inotropy curve up and to the left with greater slope
exercise
Inotropy down and to the right with lesser slope
heart failure
