List 4 similarities between cardiac and skeletal muscle
1. Both are striated & contain T-tubules~ 2. ActP provide excitation stimulus used to activate plasma membrane Ca2+ channels 3. Activated channels trigger opening of SR Ca2+ channel release ~ 4. Increase in intracellular Ca2+ activates contraction
How do cardiac and skeletal muscle T-tubules & SR systems compare?
Cardiac muscle has less developed T-tubules & SR system
How much longer is the ventricular Actp compared to skeletal muscle
100x longer (250ms)
Which has an enlarged SR, cardiac or skeletal muscle?
Which has more narrow T-tubules, cardiac or skeletal muscle?
What do L-type voltage gated Ca2+ channels do
They are located in the plasma membrane and are found in close junction to the SR. When smooth muscle depolarises, they open, thus rapid Ca2+ influx
What is the threshold value for L-type Ca2+ channela?
What do Ryanodine Receptors do?
They mediate the release of Ca2+ from the SR, so Ca2+ influx from L-Ca2+ channels bind to them, thus activating them and releasing intracellular Ca2+
What does the Na/Ca exchanger do?
It is found on the plasma membrane and it exchanges 3 Na+ ions into the cardiac myocyte for every 1 Ca2+ ion out
What does the SERCA pump do?
It resides in the SR membrane and it couples ATP hydrolysis to transport Ca2+ from the cytosol back into the SR
What is does Phospholamban do?
It helps regulate cardiac SR Ca2+ UPTAKE
Phosphloamban inhibits the SERCA pump when it is...?
Phospholamban is activated by phosphorylation @ which 3 sites?
Serine 10 by PKC, Serine 16 by PKA (cAMP dependent) & PKG (cGMP dependent), Threonine 17 by Ca2+ (calmodulin) dependent protein kinase
PKA is ....? dependent and PKG is ....? cGMP dependent
Outline the B-adrenergic receptor signalling pathway
1. NOR/ADR binds to B1-adrenergic recetors -- 2. This activates GTP binding proteins -- 3. This results in adenylyl cyclase stimulation -- 4. This leads to cAMP which leads to PKA which phosphorylates several proteins related to EC-coupling (e.g. PLB, RyRs etc), NOTE:Ach does the opposite
Outline the Gs-protein & Gi protein coupled signal transduction pathway
1. Endothelium-1 (ET-1) binds to alpha-1 or ET-a receptors, -- 2. This generates phospholipase-C, -- 3.This leads to IP3 generation which leads to increased Ca2+ release from the SR
Increased developed contractions (increased Ca2+ conc & greater availability of SR Ca2+)
Affecting cardiac relaxation (e.g. Ca2+ uptake speed increases & dissociation of Ca2+ from myofilaments also increases
RyRs can also be phosphorylated by...?
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