Cardiac Muscle 1 Flashcards
What are some general features of cardiac muscle?
Myogenic; striated; electrically coupled cells; mainly oxidative metabolism; AP causes internal Ca2+ release from SR
What cell types are in the heart?
Cardiac fibroblasts: make up majority of the cells
Myocytes: Majority of the heart mass (include purkinje and nodal cells)
endothelial cells: (vascular and endocardium)
neurons
What is around and between cells?
EC space contains collagen, vascular structures, glycocalyx like substance and empty space.
Intercalated discs at junctions between cells: nexus or gap junctions; fascia adherens or int. junctions; macula adherens or desmosomes
What is the ultrastructure of a cardiac myocyte?
Sarcolemma: surrounds myocyte and continuous with T-tubules. On surface is glycocalyx
T-tubules: invaginations of sarcolemma, and are rich in L-type calcium channels (DHPR’s). Larger than skeletal muscle.
Sarcoplasmic reticulum: intracellular, store of Ca2+; has junctional couplings with SL and t-tubules. Junctional SR has Ryrs. Calcium uptake by SERCA. NB calcium buffered by calsequestrin.
What is excitation contraction coupling?
The process(es) by which electrical changes at the surface membrane lead to changes in intracellular calcium levels which, in turn, activate contraction.
What are the four steps of EC coupling?
- Activation of the Ica (action potential arrives and the L type channels (DHPR’s) open causing small calcium in flow.
- CICR from SR occurs (Ryr’s)
- Calcium diffuses to contractile portion (sarcomere) and cross bridge cycling occurs. (TnC)
- Relaxation in two ways, through SERCA into the SR or through exchangers.
What is the role of DHPR’s?
Carry the Ica and stimulate EC coupling. Activated by deoparization and stimulated by catecholamines. Are inhibited by SR Calcium release, Mg2+.
What is in the SR membrane?
- RyR’s, which are calcium release (mainly in junctional SR)
- SR Calcium ATPase (SERCA) calcium reputake, 2 calcium for 1 ATP. regulated by phospholamban
What is a calcium transient?
Summation of calcium sparks caused by inappapriate intracellular calcium release from RyR’s
What is the summary of cardiac myocyte relaxation?
When calcium conc lowers, calcium unbinds from TnC, it is taken up into the SR by SERCA and the rest is lost by NCX. Na/K ATPase regulates Na gradient.
What are the four proteins involved in relaxation and caclium?
SERCA; NCX (efflux); SL Ca ATPase efflux; mitochondrial uniporter
Electrogenic NCX
Normally (forward mode) te NCX will exchange 3 Na in for 1 caclium out = calcium extrusion during diastole.(early repolarisation)
However in reverse mode 1 calcium in for 3 Na out (positive outside cell), so stimulated by high intracellular sodium (depolarization) (makes sense, depolarisation occurs due to high Na gradient across sarcolemma into cell, so when all the sodium rushes in, it extrudes some in exchnage for some calciu which is needed for CICR)
