Excitation contraction coupling in cardiac muscle
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What ion concentration is involved in cardiac muscle contraction?
Ca2+
What are the similarities between cardiac and skeletal muscle?
Both muscle types are striated Both contain T tubules Action potentials raise Ca2+ levels Ca2+ is crucial for contraction
What are the difference s between cardiac and skeletal muscle?
Cardiac muscle has a less developed T-tubule and sarcoplasmic reticulum system Heart contain specialised excitatory tissues The heart is electrically connected at intercalated discs (gap junctions) Ventricular action potential is 100x longer than skeletal muscle
What is excitation-contraction coupling?
The process whereby action potential triggers myocyte to contract
What is the route of electrical activity of the heart?
SA node AV node Bundle of His Bundle branches Purkinje fibres
What regulates calcium concentration in the cytoplasm?
Ryanodine receptors Plasma membrane calcium L-type channels SR calcium pump Na/Ca exchangers
What are L-type voltage gated calcium channels?
Slow Located in the plasma membrane Found in close junction of SR Requires a membrane potential greater than 30mV for activation Essential for initiation and regulation of EC coupling Smooth muscle depolarising opens them Rapid influx of Ca2+
What are ryanodine receptors?
Mediate the release of calcium ions from the SR Essential in contraction Regulated by protein-protein interactions with the L type channel
What is the Na/Ca exchanger?
Plasma membrane enzyme that exchanges 3 moles of Na for 1 mole of Ca
What is the sarcoplasmic reticulum?
Organelle Membrane bound system Encases each myofibril within a muscle cell Contains calcium pump
What is the SERCA pump?
Sarcoendoplasmic reticulum Ca-ATPase pump Resides in the SR plasma membrane Couple to ATP hydrolysis to transport calcium from cytosolic to luminal space
What is phospholamban?
Major phosphoprotein component of the SR Help regulate SR Ca2+ uptake Phosphorylation of phospholamban activates it
Describe phosphorylation of phospholamban
Can be phosphorylated at 3 different sites Serine 10 by protein kinase C Serine 16 by protein kinase A Threonine 17 by calcium calmodulin dependent protein kinase
When is phospholamban active and inactive?
Dephosphorylated version is an inhibitor of the SERCA pump Phosphorylated form dissociates from SERCA and activates the calcium pump
What links excitation and contraction?
Increased cytosolic Ca2+
What increases Ca2+ levels in the ventricular action potential?
Ca2+ influx through L-type Ca2+ channels in the sarcolemma
What stimulates ryanodine receptors?
“Trigger calcium”
What do ryanodine receptors do?
Release stored Ca2+ from the SR
What is the first step of the cardiac contraction cycle?
Cardiac myocyte contraction begins with hydrolysis of ATP to ADP by myosin
What is the second step of the cardiac contraction cycle?
Ca2+ released from the SR binds to TN-C Conformational change with tropomyosin allows myosin to form an active complex with actin
What is the third step of the cardiac contraction cycle?
Dissociation of ADP from myosin allows the myosin head toned Pulls Z lines closer together and shortens the band
What is the fourth step of the cardiac contraction cycle?
Binding of a new ATP molecule to myosin allows the actin-myosin complex to dissociate Ca2+ dissociates from TN-C
What influences cytosolic calcium concentrations?
Beta-adrenoreceptor coupled mechanism
Which nervous system regulates the heart rate?
Autonomic