Cardiac Muscle 2

Question 1

How is force modulated?

Answer 1

• increase rate of automaticity
• increase dimensions f the ventricles (increased stretch) (starlings law)
• use neurotransmitters to alter rate and Ca2+ handling
• inotropic drugs

Question 2

What is contraction force dependent of?

Answer 2

Intracellular calcium as well as total calcium (this includes reserves of buffered calcium in the SR)

TWO main ways: the amplitude and duration of the calcium transient; altered myofilament calcium sensitivity

Question 3

What factors alter calcium sensitivity?

Answer 3

Sarcomere length- ^ means greater contraction
Acidosis- more acidic means decreased force
Catecholamines- increased decreases force
caffeine!

Question 4

What pumps are activated when pH changes in myocytes?

Answer 4

More alkaline, acid loaders such as CHE and CBE

More acidic acid extruders, such as NBC and NHE

Question 5

How would heart failure best be treated drugs that increaseor decrese calcium senstivity?

Answer 5

You would think increase however this shorten relaxation time. If they have diastolic heart failure, not good. No correct answer and is circumstantial

Question 6

What is the frank starling concept?

Answer 6

An increase in end diastolic ventricular volume increases SV via a stretch induced increase in contractility

Question 7

What is the biphasic response to stretch in the heart?

Answer 7

Rapid: to do with increased myofilament sensitivity due to strecth
If you prolong stretch, the increase in force is due to the increase in the calcium transient

Question 8

What is the force frequency response?

Answer 8

That there is an increase in force of contraction with an increase in heart rate due to:-

• increased intracellular sodium (due to more depolarization), meaning more sodium calcium exchange occuring meaning more intracellular calcium.
• less time for calcium extrusion

this loads the SR, increased calcium transient

Question 9

What is the one counter intuitve aspect of sympathetic activation on the heart

Answer 9

It increased calcium influx and thus transient, but will decrease TnC sensitivity for calcium, so as to allow relaxation

Question 10

Describe Beta adrenergic stimulation of the heart

Answer 10

The heart has beta drenergic receptors, that control inotropic, lusitropic and chronotropic state of the heart.\

beta agonists stimulate adenyl cyclase, increasing cAMP, which will stimulate PKA which will phosphorylate: SL channels (^ Ica); phospholamban (increase SR uptake); SR release through RyR’s; TnI which inhibits TnC but the other stuff compensates

Question 11

What are some drugs that modulate cardiac force?

Answer 11

Digoxin (cardiotonic steroids) which inhibit the Na/K ATPase, meaning increased intracellular sodium, meaning more NCX activity, increasing Ica. Serious side effects
Sympathomimetics: B1 agonists but will desensitive
Bipyridines which inhibit phosphodiesterase, increasing cAMP