Lecture 11 - Cardiac Muscle Physiology

Question 1

Main features of cardiac muscle?

Answer 1

myogenic, striated, cells electrically coupled, oxidative metabolism, AP triggers internal CA2+ release

Question 2

Cardiac fibroblast function?

Answer 2

secrete and maintain connective tissue fibres

Question 3

Myocyte functions?

Answer 3

majority of heart mass (not cells), contraction, specialised cells (purkinje and nodal cells)

Question 4

Characteristics of cardiac muscle?

Answer 4

striated appearance, ECM containing collagen, intercalated discs containing gap junction, intermediate junctions and desmosomes

Question 5

Cardiac E-C coupling?

Answer 5

AP propagation down t-tubules activating NA channels causing depol leading to CA influx, calcium current activating ryanodine receptors to activate calcium induced calcium release, diffusion into contractile proteins leads to contrction

Question 6

DHPR?

Answer 6

carry inward CA current, AP plateau, trigger E-C coupling, inhibited by SR Ca release, activated by depol >-40mV

Question 7

Targeting DHPR?

Answer 7

stimulated: catecholamines, inhibited: Ca blockers, Mg, low plasma Ca

Question 8

Sarcoplasmic reticulm?

Answer 8

reservoir for intracellular calcium, when load is high increased QE-C coupling through Ca availability

Question 9

SR Ca buffered by?

Answer 9

calsequestrin

Question 10

SR membrane contents?

Answer 10

Ca release channels, SR Ca ATPase

Question 11

Events leading to contraction?

Answer 11

AP from adjacent cell spreads along SL, deopl opens DHPRs, Ca influx opens RyR, Ca ions bind TnC initiating cross-bridge cycle

Question 12

Events causing relxation

Answer 12

Ca reduced and unbinds from TnC, Ca pumped into SR for storage, small amount left for exchange w Na, Na gradient maintained by Na/K ATPase

Question 13

Important transporters for Myocyte relaxation?

Answer 13

SERCA (into cell), SL Ca ATPase (out of cell), SL Na/Ca exchanger (out of cell), Mitochondrial uniporter (into mitochondria)

Question 14

Steady state - if Ca efflux decreases/influx increases?

Answer 14

accumulation in cell, leading to higher SR content and increased extrusion to balance influx

Question 15

SL ATPase effectiveness?

Answer 15

minor contributer, high affinity but slow kinetics - no clinical relevance

Question 16

SL Na/Ca exchanger (electrogenic NCX)?

Answer 16

Reverse mode (Ca entry) follows depol and affects AP plateu, forward mode (Ca out), promoted by repolarization, contributes to Vm

Question 17

Forward mode stimulation?

Answer 17

depends on electrochemical gradient, stimulated by low intra Na, high intra Ca, and -ve membrane potential (reverse mode obviosuly vice versa - charge out)