Cardiac EC Coupling & Calcium Handling I

Question 1

When Calcium enters the cell from a t-tubule, it triggers

Answer 1

a larger release of Ca from the SR

Question 2

Contraction of cardiac muscle, as of skeletal muscle, is elicited by an increase in the
myoplasmic ________

Answer 2

calcium concentration

Question 3

AP releases Ca from _____

Answer 3

RyR

Question 4

binding of calcium to troponin on the thin filaments enables the force-producing interaction between the thin filaments and the myosin heads of the ________

Answer 4

thick filaments.

Question 5

Two of the important proteins are myosin, which forms the thick filament, and actin, which forms the ________

Answer 5

thin filament.

Question 6

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.

Answer 6

The NCX sodium/calcium exchanger

Question 7

binding of calcium to troponin on the thin filaments enables the force-producing interaction between the thin filaments and the _________ of the thick filaments.

Answer 7

myosin heads

Question 8

________form a class of intracellular calcium channels in various forms of excitable animal tissue like muscles and neurons

Answer 8

Ryanodine receptors (RyRs)

main source of Ca for contraction

Question 9

The NCX sodium/calcium exchanger exchanges…

Answer 9

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.

Question 10

Two of the important proteins are myosin, which forms the ____, and actin, which forms the thin filament.

Answer 10

thick filament

Question 11

binding of calcium to troponin on the ________ enables the force-producing interaction between the thin filaments and the myosin heads of the thick filaments.

Answer 11

thin filaments

Question 12

Cardiac Muscle

ECC requires entry of _____

Answer 12

external Ca2+

Question 13

Skeletal Muscle

ECC __________ require entry of external Ca2+

Answer 13

does NOT

Question 14

Ca2+ binds to troponin on thin filaments and activates contraction in _______

Answer 14

both Cardiac and Skeletal Muscle

Question 15

Located on the plasma membrane side is a type of
voltage-gated Ca2+ channel, termed the dihydropyridine receptor or DHPR

used clinically as _______

Answer 15

antihypertensive agents

Question 16

Ca2+ enters via DHPR (“L-type Ca2+ channel”) and activates _________ to cause a much larger
flux of Ca2+ from SR into myoplasm

Answer 16

RyR2

1- sequence of events during excitation, contraction and relaxation of cardiac muscle cells

Question 17

Ca2+ activates contraction by binding to troponin on ________

Answer 17

thin filaments

2- sequence of events during excitation, contraction and relaxation of cardiac muscle cells

Question 18

Ca2+ is removed from the myoplasm by:

Answer 18

(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

Question 19

SERCA2 pump located in longitudinal SR
(2 Ca2+ ions per cycle);
Ca2+ diffuses within SR to terminal cisternae, where it binds to ________

Answer 19

calsequestrin (low affinity, high capacity calcium buffer)

Question 20

NCX Na+/Ca2+ exchanger in junctional domains of _______

Answer 20

plasma membrane and t-tubules.

Question 21

PMCA pump in surface membrane (_____ per cycle).

Answer 21

1 Ca2+

Question 22

SERCA2 dominates because _______ and requires less energy because voltage is close to zero

Answer 22

longitudinal SR surrounds each myofibril

Question 23

NCX is next in importance and can be ______

Answer 23

arrhythmogenic

Question 24

In steady-state, Ca2+ released from SR is recycled back into SR by ______, and surface extrusion balances L-type Ca2+ current

Answer 24

SERCA2

Question 25

NCX exchanges _______

It can run either direction

Answer 25

3 Na for 1 Ca

Question 26

Ca released from the SR in a resting cardiomyocyte would cause _______, resulting in depolarization.

Answer 26

Na influx via NCX

Question 27

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.

Answer 27

delayed after depolarizations

Question 28

Formerly, cardiac glycosides (e.g., digitalis) was a common treatment. These inhibit Na/K ATPase and thus to reduced __________

Answer 28

extrusion of Ca via NCX.

Question 29

beta blockers, ARBs, diuretics and DHPS are used to reduce ________

Answer 29

peripheral vascular resistance.