Lecture 3: Regulation of Cardiac contraction

Question 1

Describe the cardiac length-tension relationship

Answer 1

rising phase: accounted for by increased sensitivity to Ca2+ due to increase affinity by TnC, stretching titin causes less spacing between myofilaments and more cross-bridges to form, stretch-activated Ca2+ channels open and leads to more CICR

falling phase: accounted for by increase in passive tension, leads to decrease in active tension. due to the non-contractile elements increasing stiffness and resistance to passive stretch

Question 2

Describe the Frank-Starling mechanism

Answer 2

for the whole heart, not just a sarcomere
shows how an increase in end diastolic volume (proportional to length) leads to an increased pressure (~force) systolic curve = active tension, diastolic curve = passive tension

Question 3

How does EDV increase?

Answer 3

increased ventricular filling
slower heart rate
increased venous return - exercise, venous constriction

Question 4

Describe pre-load and afterload

Answer 4

pre-load = EDV, amount of stretch the muscle has, length of sarcomere. changing preload changes the max force, but not the Vmax
afterload = pressure the heart must contract against, the aortic pressure/pressure needed to open the aortic valve. changes Vmax

Question 5

How does the different isoforms of myosin change the velocity-force relationship?

Answer 5

doesn’t change max force, changes the Vmax possible since it is determined by the rate of cross-bridge cycling