Smooth muscle contraction

Question 1

Smooth muscle dependent on

Answer 1

Ca/K AP

- extracellular Ca- unlike skeletal muscle

Question 2

Caveolae

Answer 2

On surface of sarcolemma

• have Ach and adrenergic receptors
• Ion channels- L-type Ca channels- ATP sensitive K channels- Ca sensitive K channels

Question 3

Smooth muscle action potential

Answer 3

Ca dependent

• inward depolarizing current is carried by calcium ions
• –NOT Na ions

Question 4

Unitary

Answer 4

Single unit smooth muscle

• Electrically coupled via gap junctions
• contract as single unit

Question 5

Multiunit

Answer 5

Discrete smooth muscle fibers

-each innervated by a single nerve ending

Question 6

Ca binding to calmodulin

Answer 6

Causes contraction
key regulatory protein- Myosin light chain kinase (MLCK)
-Phosphorylation of the regulatory light chain changes conformation allowing interaction with actin

Question 7

Smooth muscle relaxation

Answer 7

Phosphatase in sarcoplasm- dephosphorylates the regulatory light chain of myosin- interaction btwn actin and myosin is blocked

Also- reduction of calcium by the calcium ion pumps

Question 8

Electromechanical smooth muscle contraction

Answer 8

APs and stretch- Ca channels open

Question 9

Pharmacomechanical

Answer 9

Ligand binding to cell surface receptors

-G-protein– PLC— IP3–IP3 receptors opening in SR

Question 10

Intestine/stomach/colon/uterus

Answer 10

develop synchronous contractions and pacemakers with diastolic depolarizations

Question 11

Basal electric rhythm (BER)

Answer 11

Waves of rhythmic depolarization of intestinal smooth muscle cells
-originate at specific point then propagate

Question 12

Cells of Cajal in stomach

Answer 12

Release of NT from enteric nerve creates AP

• leads to contraction
• important for peristalsis

Question 13

Latch bridge state

Answer 13

Muscle maintains tension

• MLCP dephosphorylation of the myosin light chain while the myosin head is bound to actin
• If its dephosphorlated while head is detached then the myosin is inactive and cross bridge cycle ends

Question 14

Endothelin (ET-1)

Answer 14

Produced by vascular endothelium
once released it binds receptors
-ETa
-ETb

Question 15

ETa

Answer 15

Dominant in blood vessels

-responsible for contraction

Question 16

ETb

Answer 16

found in endothelium

• NO stimulated when ET-1 binds
• causes vasodilation

Question 17

Cardiovascular effects of endothelin

Answer 17

Systemic administration of ET-1 causes transient vasodilation and hypotension– ETb activation

• Followed by prolong vasoconstriction and HTN
• –ETa and ETb activation

Question 18

Dzs associated with elevated endothelin

Answer 18

HTN
coronary vasospasm
heart failure- ET-1 released by failing myocardium- contributes to Ca overload and hypertrophy
Pulmonary HTN- ET-1 antagonist Bosentan used to treat

Question 19

Release of Epi from adrenal medulla causes

Answer 19

Vasoconstriction in most arterioles
-Skin and gut
Vasodilation in the arterioles of the skeletal muscle and heart and bronchiolar smooth muscle in the lungs

Question 20

A1 adrenalin receptor

Answer 20

Binding of epi leads to vasoconstriction
-found in all arterioles
IP3 and Ca release- myosin phosphate active– contraction

Question 21

B2 adrenalin receptors

Answer 21

Binding of epi leads to vasodilation
cAMP- PKA- phosphorylates MLCK- inactivates MLCK
-Prevents MLCK from being activated by Ca release
-Cause relaxation