Cardiac Muscle Structure & Function

Question 1

What are the specialized features of cardiac muscles?

Answer 1

• Striated
• Not under direct neural control
• Shorter, narrower, richer in mitochondria than skeletal muscles
• ATPase activity of cardiac myosin slower than skeletal muscle but faster than SM
• Ca++ binds to troponin => regulates actin-myosin interaction

Question 2

Describe myosin

Answer 2

a

Question 3

Describe actin

Answer 3

a

Question 4

Describe troponin C

Answer 4

• Contains 1 Ca++ binding site

Question 5

Describe troponin I

Answer 5

• Contains 2 PKA phosphorylation sites (critical for adrenergic response)
• Interacts with TnC but released with phosphorylation

Question 6

Describe troponin T

Answer 6

• Binds tropomyosin

- Regulates isoform expression

Question 7

Describe tropomyosin

Answer 7

• Only alpha isoform in heart

Question 8

Describe the basic contraction-relaxation cycle

Answer 8

• AP leads to Ca++ release
• Ca++ binds to TnC
• Tn complex undergoes conformation change => moves tropomyosin out of way
• Myosin binds actin and cross bridge moves
• Ca++ is released from TnC => tropomyosin reblocks binding site => relaxation

Question 9

Describe the mechanisms of altering cross-bridge cycling in cardiac muscle

Answer 9

• many ways to regulate Ca++ flow
• Depolarization opens L-type calcium channels => calcium influx
• Calcium influx triggers more Ca++ release from SR via RyR2
• Ca++

Question 10

Describe the length-tension relationship (Frank-Starling) in cardiac muscle

Answer 10

a

Question 11

Identify sarcomeric changes associated with heart failure

Answer 11

a