bmsc 207 after midterm 2, smooth muscle, CV

Question 1

smooth muscle (shape, what it is missing)

Answer 1

spindle shaped
uninucleate
troponin and t tububles absent
intermediate filaments (non-contractile) and dense bodies (similar to z-lines) form extensive cytoskeletal structure
thin filaments are anchored to the cell membrane or dense bodies

Question 2

action potentials of smooth muscle

Answer 2

can be initiated by neural, hormonal, or mechanical stimulation

Question 3

contraction without action potentials

Answer 3

smooth muscle cells produce a wide range of membrane potentials, and in some smooth muscle, oscillations can lead to tonic contractions in the absence of action potentials.

AP usually do not occur in multiunit smooth muscle

Question 4

electrical activity in smooth muscle

Answer 4

single unit:
autonomic ap initiation
spontaneous AP

multiunit = graded potentials

Question 5

Ca activated contraction

Answer 5

both extracellular entry and intracellular release of Ca activate contraction and cytosolic Ca, is increased by 3 mechanisms:
1) Ca entry through voltage gated channels or chemically gated channels
2) Ca release from the SR
-Ca induced Ca release from RyR
IP3 Ca release
3) Ca entry through voltage-independant channels

Question 6

Ca entry through voltage-independent channels

Answer 6

depletion of Ca in the SR causes activation of store-operated channels, which cause a Ca influx across the cell membrane.
allows Ca to remain elevated and replenishes SR

STIM1 on SR
Orai-1 proteins make uip Ca channel on cell membrane

Question 7

pharmacomechanical coupling

Answer 7

drugs, excitatory neurotransmitters, and hormones can induce smooth muscle contraction independent of AP generation

Question 8

stretch-activated contraction

Answer 8

there are stretch-activated ion channels in the cell membrane of smooth muscle that, when activated, lead to depolarization.

stretch of smooth muscle causes an internal release of Ca from the SR through ryanodine receptor

Question 9

Ca signal in smooth muscle
iniating cross bridge cycling

Answer 9

differnet from cardiac and skeletal

Ca initiates a slow chain of events ultimately increasing myosin ATPase activity:
4 Ca ions bind to calmodulin, a Ca-binding protein similar to troponin C of striated muscle

the Ca calmodulin complex then activates an enzyme known as myosin light chain kinase (MLCK)
MLCK phosphorylates the regulatory light chain near the myosin head, which alters the conformation of the myosin head, increasing its ATPase activity and allows it to interact with actin.

in skeletal and cardiac muscle ATPase activity of myosin head is always high