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62 Cards in this Set

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  • Back
what are two potential results of heart failure?
1) Blood accumulates
behind the heart, causing the veins to be overfilled.
2) Too little blood flows out of the heart to provide for the needs of the body
what is the "most important intracellular messenger"?
Calcium
what effect does calcium entry have on resting myocytes?
it causes contraction
does calcium enter the cell via passive or active processes?
passive. the gradient from outside to inside is downhill.
what must happen to the intracellular calcium for the heart to relax?
it must be pumped out, uphill.
how great is the Ca++ concentration gradient across the plasma membrane?
10,000 times
why is calcium so concentrated outside the cell?
calcium phosphate is insoluble, and due to large amount of phosphate in cell, calcium is excluded.
what impact on action potentials does calcium influx have on myocytes?
causes depolarization and subsequent contraction
which proteins in the cell bind Ca++ with high affinity?
E-F Hand proteins
is Ca++ diffusion enough to trigger an action potential in adult cardiac myocytes? why or why not?
no; diffusion is too slow to alone cause a sufficient AP in adult myocytes
where are intracellular Ca++ stores located?
sarcoplasmic reticulum (SR)
what is the sarcotubular network?
part of SR that pumps Ca++ out of cytosol
what occurs at sarcolemmal cisternae?
electrical signals from t-tubules are transmitted to SR
what is the name for intersection of t-tubules and sarcolemmal cisternae?
dyads
Why are Ca++ release channels often called 'ryanodine receptors'?
because they bind well to ryanodine even though it has nothing to do with their function
what is another name for ryanodine receptors?
feet
what is the relationship between ionic environment of t-tubules with that of the exterior of the cell?
identical. the t-tubules are continuous with the extracellular environment
which channels are responsible for bringing extracellular Ca++ into cell?
L-type Calcium channels
which 2 channels pump Ca++ from inside cell to ECF?
1) Na+/Ca++ pump
2) Plasma membrane Ca++ pump (PMCA)
through what channel does Ca++ exit SR into the cytosol?
SR Ca Release Channels
through what channel is Ca++ brought back into SR from cytosol?
SR Ca Pump
which channel provides the "small bang" that triggers the "large boom"?
L-type Ca++ channels
the Na+/Ca++ exchanger created which type of current? what is driving force of pump?
inward current due to Na+ current; driving force is Na+ conc. gradient
why can Na+/Ca++ exchanger cause problems in heart failure patients?
too much Ca++ in heart of heart failure patients causes action of Na/Ca pump, creating influx of Na which could cause contractions and MI's.
where is location of feet proteins?
between sarcolemmal cisternae and t-tubules
how many Ca++ 'holes' does each foot contain?
4
which proteins binds Ca to initiate muscle contraction?
Troponin C
Which ATP-dependent pump is responsible for sequestering Ca in SR?
SERCA2a
which protein regulates the SERCA2a channel?
phospholamban
which protein regulates phospholamban?
cyclic ATP-dependent protein kinase (PK-A)
what effect does phosphorylation have on phospholamban? phosphorylation is done in response to what?
more complete Ca sequestration, more complete relaxation, more forceful subsequent contractions; done in response to sympathetic activation
which protein helps to keep Ca inside SR and prevent from leaking out feet?
Calsequestrin
a sarcomere sits between which two points?
z-lines
how many A bands are present in a sarcomere? I bands?
1 A band; 2 half-I bands
cross-bridges in myocytes connect _______ with ________.
thin filaments; thick filaments
Z lines are composed mainly of which protein?
Titin
at rest, what is the position of cross-bridges in myocyte?
at right angles to thick and thin filaments
thick filaments are composed of _______. thin filaments are composed of __________.
myosin tails; actin
which chain of myosin, heavy or light, hydrolyzes ATP?
heavy chain
ATP energy is used to do what in myosin?
used to move cross bridge and force muscles to contract
of what are cross-bridges composed?
myosin heads
_______ is the name for the protein which resides in the groove between 2 actin thin filaments.
tropomyosin
what kind of protein is Troponin C?
E-F Hand
When Ca is not bound to Troponin C, ________ inhibits actin-myosin interactions
Troponin I
What is the role of Troponin T?
Binds Troponin I and Troponin C to Tropomyosin
Which protein on the thin filament is physically in the way of actin-myosin binding?
Tropomyosin
which, preload or afterload, is related to pressure as the ventricle is filling? which is related to ejecting pressure?
preload - filling; afterload - ejecting
what is the consequence of maximum afterload? of zero afterload?
muscle cannot shorten; cross-bridges cycle at maximum rate
when afterload is ________, internal work increases.
increases
maximal force is related to what factor?
number of actin-myosin cross bridges
Vmax is related to what factor?
turnover rate of actin-myosin cross bridges
Vmax is maximum at _______ afterload; maximal force is maximum at __________ afterload.
zero; maximum
Vmax is determined mainly by what?
myosin heavy chain isoform
what happens to muscle tension when muscle length is greater than max length?
decreases.
muscle length is determined by preload or afterload?
preload
optimally, does the heart operate on the ascending or descending limb of tension-length curve?
ascending
what is the result of an increase in venous return during descending limb of tension-length curve?
vicious cycle
what does the heart's 'low compliance' mean?
it is highly stiff
a dilated heart usually operates on which limb of the tension-length curve?
descending
at peak tension, what percentage of myosin and actin filaments are interacting?
100%
what is a change in contractility for the heart? how is this achieved?
a change in ability to do work without directly changing preload or afterload; achieved by drugs (digitalis), sympathetic stimulation
what is the most important way to modify contractility in myocytes?
increase Ca binding