Deck 14: Smooth Muscle

Question 1

An increase in smooth muscle tension can occur at a given intracellular [Ca⁺⁺] in response to:

A)Opening of K⁺ channels in the smooth muscle membrane.
B)Inhibition of myosin phosphatase by Rho kinase in the smooth muscle.
C)Cyclic adenosine monophosphate (cAMP)-dependent phosphorylation of myosin light-chain kinase in the smooth muscle.
D)Release of nitric oxide from adjacent endothelial cells.
E)Hyperpolarization of the smooth muscle membrane.

Answer 1

B

Question 2

Endogenous agonists such as adenosine and prostacyclin,as well as $\beta$ ₂-adrenergic receptor agonists,can elevate cAMP concentration in smooth muscle.The elevation of cAMP in the smooth muscle results in activation of cAMP-dependent signaling pathways in the smooth muscle.This activation typically:

A)Promotes relaxation,partly because of activation of myosin phosphatase.
B)Promotes contraction,partly because of activation of potassium channels.
C)Promotes relaxation,partly because of activation of Rho kinase.
D)Promotes contraction,partly because of inhibition of InsP3 production.
E)Promotes relaxation,partly because of inhibition potassium channels.

Answer 2

Promotes relaxation,partly because of activation of myosin phosphatase.

Question 3

A variety of stimuli can elevate cyclic guanosine monophosphate (cGMP)concentration in smooth muscle,which results in activation of cGMP-dependent signaling pathways in the smooth muscle.This activation typically:

A)Promotes relaxation,partly because of inhibition of myosin phosphatase.
B)Promotes contraction,partly because of decreased endothelin production.
C)Promotes relaxation,partly because of activation of potassium channels .
D)Promotes contraction,partly because of inhibition of InsP3 production.
E)Promotes relaxation,partly because of activation of voltage-gated Ca channels.

Answer 3

C

Question 4

The latch property of smooth muscle concerns the ability of the smooth muscle to maintain:

A)A relaxed state independent of cytosolic Ca⁺⁺ level.
B)Force while decreasing the rate of energy utilization.
C)The rate of InsP3 production after agonist removal.
D)Force in the absence of myosin light-chain phosphorylation.
E)Membrane potential independent of contractile state.

Question 5

In smooth muscle,actin and myosin filaments:

A)Are organized into sarcomeres and aligned in a striated pattern.
B)Overlap,with the actin filaments anchored at dense bodies.
C)Overlap and contain a tropomyosin-troponin complex on the actin filament.
D)Require phosphorylation of the myosin heavy chain to initiate muscle contraction.
E)Typically generate contractile force in the absence of cytosolic Ca⁺⁺.

Question 6

Smooth muscle can contract without a change in membrane potential after:

A)Stimulation of $\beta$ -adrenergic receptors in the smooth muscle.
B)Inhibition of Rho kinase in the smooth muscle.
C)Stimulation of InsP3 production in the smooth muscle.
D)Stimulation of nitric oxide release from endothelial cells.
E)Stimulation of K⁺ channels in the smooth muscle.

Question 7

During exercise,skeletal muscle can release local factors,such as adenosine,which can relax neighboring vascular smooth muscle and thus promote vasodilation in the exercising muscle.The mechanism by which adenosine promotes relaxation of smooth muscle typically involves:

A)Inhibition of K⁺ channels in the vascular smooth muscle.
B)Stimulation of InsP3 production in the vascular smooth muscle.
C)Stimulation of release of endothelin from adjacent endothelial cells.
D)Stimulation of cAMP production in the vascular smooth muscle.
E)Activation of voltage-gated Ca⁺⁺ channels in the vascular smooth muscle.

Question 8

A variety of smooth muscle relaxants can promote the occurrence of Ca⁺⁺ sparks beneath sarcolemma of smooth muscle.The Ca⁺⁺ sparks are thought to originate from a local activation of the ryanodine receptor,just beneath the sarcolemma.These Ca⁺⁺ sparks promote relaxation by:

A)Activating the Na⁺-Ca⁺⁺ antiporter in the smooth muscle.
B)Activating the Ca⁺⁺-dependent phosphatase calcineurin in the smooth muscle.
C)Activating Ca⁺⁺-dependent K⁺ channels in the smooth muscle.
D)Promoting myosin light-chain phosphorylation in the smooth muscle.
E)Activating Rho kinase in the smooth muscle.

Question 9

Decreased cytosolic Ca⁺⁺ in smooth muscle typically promotes relaxation by:

A)Closing Ca⁺⁺-activated K⁺ channels in the smooth muscle.
B)Reducing myosin light-chain kinase activity in the smooth muscle.
C)Reducing nitric oxide release from endothelial cells.
D)Reducing Ca⁺⁺ influx through transient receptor potential vanilloid (TRPV)channels in the smooth muscle.
E)Reducing production of inositol 1,4,5-triphosphate (InsP3)in the smooth muscle.