Flashcards in Lecture 11 - Cardiac Muscle Physiology Deck (17):
Main features of cardiac muscle?
myogenic, striated, cells electrically coupled, oxidative metabolism, AP triggers internal CA2+ release
Cardiac fibroblast function?
secrete and maintain connective tissue fibres
majority of heart mass (not cells), contraction, specialised cells (purkinje and nodal cells)
Characteristics of cardiac muscle?
striated appearance, ECM containing collagen, intercalated discs containing gap junction, intermediate junctions and desmosomes
Cardiac E-C coupling?
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
carry inward CA current, AP plateau, trigger E-C coupling, inhibited by SR Ca release, activated by depol >-40mV
stimulated: catecholamines, inhibited: Ca blockers, Mg, low plasma Ca
reservoir for intracellular calcium, when load is high increased QE-C coupling through Ca availability
SR Ca buffered by?
SR membrane contents?
Ca release channels, SR Ca ATPase
Events leading to contraction?
AP from adjacent cell spreads along SL, deopl opens DHPRs, Ca influx opens RyR, Ca ions bind TnC initiating cross-bridge cycle
Events causing relxation
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
Important transporters for Myocyte relaxation?
SERCA (into cell), SL Ca ATPase (out of cell), SL Na/Ca exchanger (out of cell), Mitochondrial uniporter (into mitochondria)
Steady state - if Ca efflux decreases/influx increases?
accumulation in cell, leading to higher SR content and increased extrusion to balance influx
SL ATPase effectiveness?
minor contributer, high affinity but slow kinetics - no clinical relevance
SL Na/Ca exchanger (electrogenic NCX)?
Reverse mode (Ca entry) follows depol and affects AP plateu, forward mode (Ca out), promoted by repolarization, contributes to Vm