Muscle Physiology III

Question 1

inc. Ca++ n the Myosin Light

Chain Kinase

Answer 1

-Myosin Light
Chain Kinase
activated
-phophoryte 
-CONTRACTION

Question 2

Smooth muscle contraction -Myosin II:

Answer 2

• 2 myosin heavy chain
• 2 myosin light chains (MLC):
• Essential MLC
• Regulator MLC

Question 3

Smooth muscle contraction component

Answer 3

Myosin light chain kinase (MLCK)
Myosin light chain phosphatase (MLCP)
Calmodulin (regulator of contraction; homologous of Troponin C)
Ca++ (activator of contraction)

Question 4

Voltage-gated 1,4 dihydropyridine calcium channels

Answer 4

Electromechanical coupling

Question 5

Ligand-gated calcium channels

Answer 5

Pharmacomechanical coupling

Question 6

Stretch-activated calcium channels

Answer 6

Myogenic regulation in arterioles (microvascular resistance)

Question 7

Leak calcium channels

Answer 7

Unregulated

Mechanical stretch promotes inward movement of Ca++

Question 8

Ca++ channel bocer

Answer 8

-Inhibit voltage-dependent L-type calcium channels - Dec .muscle contractility

Question 9

Dihydropyridine CCB

Answer 9

-Act on vascular smooth muscle
Amlodipine, clevidipine, nicardipine, nifedipine, nimodipine
Clinical use: Hypertension, prevention of cerebral vasospasm (nimodipine)

Question 10

Non-dihydropyridine CCB

Answer 10

-Act on heart:
-Diltiazem, verapamil
Clinical use: atrial fibrillation

Question 11

cAMP pathway

Answer 11

-Enhances Ca++
reuptake
-RELAXATION

Question 12

Beta-2 receptors are Gs-protein coupled:

Answer 12

Bronchial smooth muscle relaxation (bronchodilation)
• Uterine smooth muscle relaxation during pregnancy
• Blood vessels relaxation (vasodilation) in the skeletal muscle

Question 13

Albuterol, levalbuterol, salmeterol, salbutamol (inhalation)

Answer 13

Bronchial smooth muscle relaxation –Bronchodilation

Clinical use: Bronchial Asthma

Question 14

Terbutaline

Answer 14

Uterine smooth muscle relaxation in pregnant women –Tocolysis
Clinical use: premature labor

Question 15

milrinone

Answer 15

Selective PDE-3 inhibitor
Phosphodiesterase 3 (PDE-3) converts cAMP into AMP in cardiac and smooth muscle
-Clinical use: short-term use in acute decompensated Heart Failure

Question 16

milrinone -In cardiomyocytes:

Answer 16

inc . cAMP - inc. Ca++ influx - inc. Inotropy and Chronotropy

Question 17

milrinone -In vascular smooth muscle

Answer 17

inc. cAMP – Inhibition of MLCK activity – General Vasodilation

Question 18

Nitric Oxide (NO)
pathway

Answer 18

-cGMP
-Open K+ channels:
hyperpolarization
-Inhibit Ca++ entry
-MLCP

Question 19

Nitrates

Answer 19

Increase Nitric Oxide in vascular smooth muscle
Dilate veins&raquo_space; arteries …… Decrease PRELOAD
Nitroglycerine, isosorbide denitrate, isosorbide mononitrate
Clinical use: angina, acute coronary syndrome

Question 20

Hydralazine

Answer 20

inc. cGMP –vascular smooth muscle relaxation
Dilate arterioles > veins …… Decrease AFTERLOAD
Clinical use: severe hypertension (acute treatment); safe during pregnancy

Question 21

Nitroprusside

Answer 21

inc. cGMP –vascular smooth muscle relaxation

Question 22

Ca++ RELEASE

Answer 22

• CICR
• IP3
• Contraction

Question 23

mechanism o RELAXATION

Answer 23

• dec. Ca++

- dec. MLCK activity

Question 24

mechanism o RELAXATION-Cell repolarization

Answer 24

Decrease influx of Ca++

Question 25

mechanism o RELAXATION-Reuptake of Ca++ to the SR:

Answer 25

SERCA pump

Question 26

mechanism o RELAXATION-Plasma Membrane Ca++ ATPase Pump

Answer 26

Promote Ca++ efflux

Question 27

mechanism o RELAXATION-Na+/Ca++ exchange mechanism

Answer 27

Promote Ca++ efflux

Question 28

Latch mechanism or state

Answer 28

ns its full force of contraction despite reduced amount of continuing excitation and lesser energy required for comparable sustained skeletal muscle contraction -Low ATP utilization • Lower Ca++ concentration requirements

Question 29

Latch mechanism or state-Importance

Answer 29

can maintain prolonged tonic contraction in smooth muscle for hours with little use of energy

Question 30

Latch mechanism or state-Cause (hypothesis):

Answer 30

myosin dephosphorylation while still attached to actin during the crossbridge cycle

Question 31

Ca++ sensitization

Answer 31

Decrease MLCP activity – Increase MLC phosphorylation

Question 32

Ca++ de-sensitization

Answer 32

Increase MLCP activity – Decrease MLC phosphorylation