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36 Cards in this Set
- Front
- Back
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Describe a cardiac muscle
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Striated muscle that contains sarcomeres. THey are short with branching fibers that form physical contacts with other cardiac cells called Intercalated Discs. they are about 20 um in length
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Intercalated disc
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attachment sites/low resistance pathways that allow the heart to act as a functional unit
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Compare the T-tubules in cardiac muscle cells to those in skeletal muscles
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They are wider and allow ample metabolite exchange
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Vinculin
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this is an attachment protein that has been identified at each of the intercalated disc and aids in transmitting force from one cell to the next
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T/F Cardiac cells can utilize lipid as a source of energy
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True. lipid cells are found near the mitochondria
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Functional syncytium
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The functional connections or gap junctions at the intercalated discs result in the spread of APs from one cell to the next so the heart contracts as it were a single unit
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Voltage-gated calcium channel what is another name for this and what purpose does it serve
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Ca2+ moves into an intermediate compartment so it can participate in a subsequent contraction, some is involved in the contraction
(L-type Ca2+ channel) |
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Na+/Ca++ exchanger
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This exchanger contains negatively charged parts and can move 3Na+/Ca++ in either direction
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Which direction does the Na+/Ca++ exchanger move Ca2+_ during diastole or when the cardiac muscle is at rest?
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Ca++ out
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What happens when the Na+/K+ pump stops working?
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Intracellular Ca++ would increase
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How is cardiac muscle Ca++ release different than in skeletal muscle?
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Ca++ enters through L-type Ca++ channels, causing a much larger amount of Ca++ to be released from the SR stores.
calmodulin kinase serves as the switch that llinks the DHPR and RyR1 functions |
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Phospholamban - dephosphorylated, what does it do
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resides next to the calcium pump limiting the pump rate in the SR. (during contraction)
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Phospholamban - phosphorylated, what does it do and how do we phosphorylize it?
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phosphorylation makes this move away from the calcium pump, which allows Ca++ to reenter the SR, leading to relaxation of the cardiac muscle.
cAMP- protein kinases help achieve this. Epinephrine can also do this |
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T/F Cardiac muscle undergoes tetanic contraction
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False. It always twitches
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Define contractility of cardiac muscles in terms of interactions between contractile proteins
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1.) depends on number of cross-bridge interactions
2.) depends on the maximal rate of myosin ATPase 1 depends on Ca++ availability 2 depends on the phosphorylation state of myosin |
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What can regulate cardiac contractility (alteration in myosin molecule)?
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Tonic control of contractility, endocrine imbalances, aging, and chronic hemodynamic overloading, phasic control of velocity
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What can regulate cardiac contractility (alteration in the content of contractile proteins)?
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work-induced hypertrophy results from hemodynamic overload. Heart size/mass increases
Starvation decreases protein content adn weakens the heart |
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What causes hypertrophic cardiomyopathy?
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Defects in sarcomeric proteins such as B myosin, troponin T and a myosin binding protein
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How can the Na+/Ca++ exchange increase cardiac contractility? Decrease cardiac contractility?
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Na+ in and Ca++ out = decreased contractility
Na+ out and Ca++ in = increased contractility |
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What is the effect of phospholamban phosphorylation?
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It causes an increased rate of relaxation due to reuptake of Ca++ in the SR (phospholamban moves away from the Ca++ pump)
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What is the effect of cardiac glycosides on contractility? give one example of a cardiac glycoside
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Digoxin.
Inhibition of Na-K pump and permission of Ca++ to accumulate within the cardiocytes. Increases contractility |
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What is the effect of Protein Kinase phosphorylation? What is its target (in cardiac muscle)? How does this effect contraction speed?
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Phosphorylate myosin, increasing its activity and leads to increased contraction speed
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What are epinephrine and norepinephrine's effects on glycogenolysis and how does this pertain to contractile events?
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Increase the rate of glycogenolysis to mobilize energy for fueling of contractile events.
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What are the functional significances of contractility changes in terms of Ca++ and myosin phosphorylation?
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Increased Ca++ increase the force output of the muscle
Phosphorylation of Myosin increases the velocity of shortening |
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What is the net result of B Adrenergic stimulation of the cardiocytes?
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Ca++ increases (increases force of contraction)
Myosin is phosphorylated (increases velocity of contraction) Increase rate of relaxation - greater time to fill the heart with blood Increase in energy mobilization (via increased glycogenolysis) |
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T/F Cardiac Muscle has sarcomeres
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T
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T/F Troponin is present in cardiac muscles
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T
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Does myosin phosphorylation occur in cardiac muscles?
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yes
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T/F T-tubules are present in cardiac muscles
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T
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T/F The SR is NOT present in cardiac muscles
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False
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T/F Phospholamban is present in cardiac muscles
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T
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How involved is EC calcium in Cardiac Muscles?
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Moderately involved. See notes for more details!!!
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T/F Na-Ca Exchange is present in cardiac muscles
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T
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T/F Cardiac muscles feature a functional syncytium
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T
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What is the function of nerves in cardiac muscles?
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to modulate activity
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Describe the following "parameters" of cardiac muscles, whether they are present or not...
sarcomere, troponin, myosin phosphorylation, t-tubules, SR, Phospholamban, Na-Ca exchange, functional syncytium |
Present: Sarcomere, troponin, myosin phosphorylation, t-tubules, SR, Phospholamban, Na-Ca Exchange, Functional Syncytium
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