Cardiac Myocyte Physiology

Question 1

Tissue level structure

Answer 1

Most of myocardial volume composed of myocytes joined at intercalated discs

Gap junctions allow ions, small molecules, and electrical signals to pass betweencells

Myocardium forms a functional syncytium

Question 2

Ca concentrations

Answer 2

EC - 2mM
Insides SR - 2mM

Near myofilaments - 200nM in diastole and 2 uM in systole

Question 3

Describe excitation contraction coupling

Answer 3

See notes

Question 4

Phospholamban

Answer 4

Inhibits SERCA activity in its dephosphorylated state

This inhibits relaxation

Question 5

Thin fiilament activation

Answer 5

Calcium binds to troponin and exposes actin sites that can then binds cross bridge of myosin and generate froce

Question 6

Leaky ryanodine receptors

Answer 6

Less systolic contraction
Slower relaxation

Perturbs normal intracellular Ca levels so arrhythmias

Question 7

Passive portion of L-T diagram

Answer 7

Reflects the elastic stretch of titin molecules and ECM (collagen)

If collagen increases, then force will increase for a given length

Question 8

Order of things that happens

Answer 8

Stimulus….Ca concentration…force

Question 9

Active portion of L-T diagram

Answer 9

Myocardium

Always operates on the ascending limb

Basically as the length increases, the tension force will also increase

Question 10

Isometric and isotonic contractions

Answer 10

Isometirc - fixed lenth

Isotonic - loaded and measure the distance shortened

Question 11

After-loaded contraction

Answer 11

Isometric contractions perform mechanical work

If the force is smaller, the speed at which contraction occurs will be shorter…lenght change will also be greater

Vice versa

Higher BP means greater force

Maximum shortening velocity occurs at lowest force

Question 12

Cross bridge cycle

Answer 12

1 - acitvation of myosin head by ATP hydrolysis

2 - cross birdge formation

3 - power stroke from phoshate release

4 - ADP leaves and ATP binds…actin dissociates

More P - smaller force…more ADP - greater force

Question 13

B adrenergic stimulation in general

Answer 13

More force and contracts and relaxes faster

Question 14

Beta-adrenergic effects mech

Answer 14

Modulation through L-type Ca channels

Phosphorylation of phospholamban which relieves its inhibition of SERCA so faster relaxation

Question 15

Contractile force as a function of Ca

Answer 15

higher Ca = higher force

Question 16

B-adrneergic activation effects on force and calcium relationship

Answer 16

Enahnce max force

More sensitivie to Ca

Speeds cross-bridge cycle

Question 17

Phosphorylation from B-adrenergic

Answer 17

Troponin 1
Myosin regulatory light chain
Myosin-binding protein C

(Also phospholamban)