Lecture 7: Excitation-Contraction coupling

Question 1

Why do the methods of increased contractile force for skeletal muscle not apply to cardiac muscle?

Answer 1

tetany = doesn’t work since AP takes too long during twitch
increased recruitment = doesn’t work since 100% of cardiac myocytes recruited

instead - change contractile force

Question 2

Describe how contractile force is regulated

Answer 2

through sympathetic/parasympathetic regulation. NE=beta1=Gs=AC=ATP–>cAMP=activate PKA
PKA phosphorylates phospholamban, RyR, Cav1.2, and TnI
phospholamban = take brakes of SERCA, faster relaxation, more sequestration
RyR= fractional opening increases, more Ca2+ released from SR
CAv1.2 = greater open probability, more CICR
TnI = lesser TnC affinity for Ca, quicker relaxation

Question 3

Describe pharmocological regulation

Answer 3

sympathomimetics: cocaine = blocks NE re-uptake, amphetamines = release NE from storage vesicles
sympatholytics = beta-blockers (propanolol)

Question 4

Define inotropy vs dromotropy vs chronotropy

Answer 4

force of contraction vs. rhythmicity vs. timing

Question 5

Describe the 2 ways contractile force can be regulated

Answer 5

length-dependent (Frank-Starling, L-T rel) or length-independent (increased contractility)