Cardiac EC Coupling & Calcium Handling I Flashcards
When Calcium enters the cell from a t-tubule, it triggers
a larger release of Ca from the SR
Contraction of cardiac muscle, as of skeletal muscle, is elicited by an increase in the
myoplasmic ________
calcium concentration
AP releases Ca from _____
RyR
binding of calcium to troponin on the thin filaments enables the force-producing interaction between the thin filaments and the myosin heads of the ________
thick filaments.
Two of the important proteins are myosin, which forms the thick filament, and actin, which forms the ________
thin filament.
exchanges 3 Na for 1 Ca and can run either direction:
calcium efflux in exchange for sodium influx or calcium influx in exchange for sodium efflux.
The NCX sodium/calcium exchanger
binding of calcium to troponin on the thin filaments enables the force-producing interaction between the thin filaments and the _________ of the thick filaments.
myosin heads
________form a class of intracellular calcium channels in various forms of excitable animal tissue like muscles and neurons
Ryanodine receptors (RyRs)
main source of Ca for contraction
The NCX sodium/calcium exchanger exchanges…
3 Na for 1 Ca and can run either direction
ca efflux in exchange for na influx or
ca influx in exchange for na efflux.
Two of the important proteins are myosin, which forms the ____, and actin, which forms the thin filament.
thick filament
binding of calcium to troponin on the ________ enables the force-producing interaction between the thin filaments and the myosin heads of the thick filaments.
thin filaments
Cardiac Muscle
ECC requires entry of _____
external Ca2+
Skeletal Muscle
ECC __________ require entry of external Ca2+
does NOT
Ca2+ binds to troponin on thin filaments and activates contraction in _______
both Cardiac and Skeletal Muscle
Located on the plasma membrane side is a type of
voltage-gated Ca2+ channel, termed the dihydropyridine receptor or DHPR
used clinically as _______
antihypertensive agents
Ca2+ enters via DHPR (“L-type Ca2+ channel”) and activates _________ to cause a much larger
flux of Ca2+ from SR into myoplasm
RyR2
1- sequence of events during excitation, contraction and relaxation of cardiac muscle cells
Ca2+ activates contraction by binding to troponin on ________
thin filaments
2- sequence of events during excitation, contraction and relaxation of cardiac muscle cells
Ca2+ is removed from the myoplasm by:
(i) SERCA2 pump located in longitudinal SR
(ii) NCX Na+/Ca2+ exchanger in junctional domains of plasma membrane and t-tubules.
3- sequence of events during excitation, contraction and relaxation of cardiac muscle cells
SERCA2 pump located in longitudinal SR
(2 Ca2+ ions per cycle);
Ca2+ diffuses within SR to terminal cisternae, where it binds to ________
calsequestrin (low affinity, high capacity calcium buffer)
NCX Na+/Ca2+ exchanger in junctional domains of _______
plasma membrane and t-tubules.
PMCA pump in surface membrane (_____ per cycle).
1 Ca2+
SERCA2 dominates because _______ and requires less energy because voltage is close to zero
longitudinal SR surrounds each myofibril
NCX is next in importance and can be ______
arrhythmogenic
In steady-state, Ca2+ released from SR is recycled back into SR by ______, and surface extrusion balances L-type Ca2+ current
SERCA2
NCX exchanges _______
It can run either direction
3 Na for 1 Ca
Ca released from the SR in a resting cardiomyocyte would cause _______, resulting in depolarization.
Na influx via NCX
Depolarization via NCX as a consequence of abnormal diastolic SR Ca release has been suggested to be a trigger for ________ that give rise to arrhythmias.
delayed after depolarizations
Formerly, cardiac glycosides (e.g., digitalis) was a common treatment. These inhibit Na/K ATPase and thus to reduced __________
extrusion of Ca via NCX.
beta blockers, ARBs, diuretics and DHPS are used to reduce ________
peripheral vascular resistance.
