Excitation contraction coupling in cardiac muscle

esbaid's version from 2016-01-28 14:50

Section 1

Question Answer
List 4 similarities between cardiac and skeletal muscle1. 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 muscle100x longer (250ms)
Which has an enlarged SR, cardiac or skeletal muscle?Skeletal muscle
Which has more narrow T-tubules, cardiac or skeletal muscle?Skeletal muscle
What do L-type voltage gated Ca2+ channels doThey 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?-30mV
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...?Dephosphorylated
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 dependentcAMP & cGMP
PKC phsophorylates?Serine 10

Section 2

Question Answer
Cardiac myocyte contraction begins with...?Hydrolysis of ATP to ADP by myosin
Ca2+ released from the SR binds to...? which causes a conformational change in....? resulting in...?Troponin-C, Tropomyosin, resulting in an actin myosin cross bridge
What triggers the myosin head to bend and what does this bending do?Dissociation of ATP from the myosin, this bending pulls Z-LINES closer together & shortens the band (this is known as a rigor complex)
How is the actin myosin cross bridge dissociated?A new ATP molecule binds to the myosin head

Section 3

Question Answer
What are Chronotropic agents?They are drugs that alter heart rate
Outline the B-adrenergic receptor signalling pathway1. 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 pathway1. 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
Ionotropic means?Increased developed contractions (increased Ca2+ conc & greater availability of SR Ca2+)
Lusitropic means?Affecting cardiac relaxation (e.g. Ca2+ uptake speed increases & dissociation of Ca2+ from myofilaments also increases
RyRs can also be phosphorylated by...?PKA