Deck 13: Cardiac Muscle

Question 1

Cardiac muscle cells in the atria are capable of contracting spontaneously because of a spontaneous depolarization that results from:

A)An inward current through a hyperpolarization-activated channel.
B)Cyclic changes in the activity of Na⁺,K⁺-ATPase.
C)Slow leak of Ca⁺⁺ through the dihydropyridine receptor.
D)Cyclic changes in the activity of the sarcolemmal Ca⁺⁺ pump.
E)Cyclic changes in the activity of SERCA.

Answer 1

A

Question 2

Calsequestrin in cardiac muscle:

A)Acts as a high-affinity Ca⁺⁺ buffer in the cytosol.
B)Acts as a low-affinity Ca⁺⁺ buffer in the SR lumen,near the ryanodine receptor.
C)Promotes Ca⁺⁺ accumulation by the mitochondria.
D)Increases the Ca⁺⁺ affinity of the sarcolemmal Ca⁺⁺ pump.
E)Facilitates myosin binding to the actin thin filament.

Answer 2

B

Question 3

Relaxation of cardiac muscle typically requires:

A)Myosin light-chain dephosphorylation.
B)Activation of the ryanodine receptor.
C)Ca⁺⁺ uptake by the sarcoplasmic reticulum (SR).
D)Phosphorylation of phospholamban.
E)Activation of the dihydropyridine receptor.

Answer 3

C

Question 4

Epinephrine increases the force of contraction of cardiac muscle by:

A)Increasing the amount of Ca⁺⁺ in the SR for release to the cytosol.
B)Increasing the level of myosin light-chain phosphorylation.
C)Inhibiting the ryanodine receptor.
D)Increasing Ca⁺⁺ extrusion through the sarcolemmal Ca⁺⁺ pump.
E)Shortening the duration of the action potential.

Question 5

The force of contraction of cardiac muscle is typically increased by:

A)An increase in Ca⁺⁺ extrusion by the Na⁺-Ca⁺⁺ antiporter in cardiac muscle.
B)An increase in myosin phosphorylation in cardiac muscle.
C)A decrease in cytosolic [Ca⁺⁺] in the cardiac muscle.
D)β-Adrenergic stimulation of the cardiac muscle.
E)Recruitment of more cardiac muscle cells.

Question 6

Contraction of cardiac muscle typically requires:

A)Ca⁺⁺ influx through voltage-gated Ca⁺⁺ channels to trigger a rise in cytosolic [Ca⁺⁺].
B)Ca⁺⁺ influx through voltage-gated Ca⁺⁺ channels,which is sufficient to support contraction.
C)Activation of myosin light-chain kinase (MLCK).
D)Phosphorylation of myosin heavy chain.
E)Ca⁺⁺ influx through the Na⁺-Ca⁺⁺ antiporter.

Question 7

Mutations in the cardiac ryanodine receptor have been associated with cardiac arrhythmias.Specifically,a mutation in the cardiac ryanodine receptor that increases Ca⁺⁺ efflux from the SR promotes the development of delayed afterdepolarizations by:

A)Decreasing the activity of calcineurin.
B)Increasing Ca⁺⁺ efflux through the Na⁺-Ca⁺⁺ antiporter.
C)Increasing mitochondrial Ca⁺⁺ uptake.
D)Decreasing actin-myosin interactions.
E)Increasing the activity of K⁺ channels.

Question 8

Stretching cardiac muscle results in an increase in the force of contraction as a result of:

A)Activation of K⁺ channels.
B)An increase in the sensitivity of actin-myosin interactions to Ca⁺⁺.
C)Phosphorylation of the ryanodine receptor.
D)Increased phosphorylation of troponin I.
E)Increased Ca⁺⁺ influx through the Na⁺-Ca⁺⁺ antiporter.

Question 9

The mechanisms underlying the development of cardiac hypertrophy are complex,although relaxation abnormalities that result in chronic elevation of cytosolic Ca⁺⁺ level appear to promote the development of hypertrophy through:

A)Stimulation of the sarcolemmal Ca⁺⁺ pump.
B)Ca⁺⁺ binding to troponin I.
C)Activation of calcineurin.
D)Inhibition of Ca⁺⁺/calmodulin-dependent protein kinase.
E)Opening of Ca⁺⁺-activated K⁺ channels.