Lecture 9 Flashcards
How does excitation contraction coupling occur at the cellular level?
The cell depolarises the cell membrane from -80mV to +10mV where it excites the contractions for the cell
What does electrolyte excitation elevate?
Cytoplasmic ca2+ in the cell, interacts with the myofilament proteins of the cell to give the resulting contraction
What does the structure of the ventricular cardiomyocytes mean?
Proves the function - ca2+ contraction
What type of muscle are heart muscles?
Striated heart muscle
What is found in striated heart muscle?
Lots of mitochondria
Why are heart muscles called striated muscles?
Because they have alternative light and dark banding
What are the light and dark bands?
Sarcomeric structures - striated parents of the cardiomyocytes
Why do striations occur?
Because of the rigid arrangements of the thick and thin filaments of the sarcomere structures
What are sarcomeres defined by?
Defined by the boundary of the Z lines
How far apart are the Z lines?
2 microns apart
What are Z lines?
Scaffolding structures that hold in place the thin filaments
What do you see in the middling portions?
Much more myofilament activity as this is where the invaginations of the thick and thin filaments are
What are sacromeric structures?
The individual contractile units within the cell - control with electrical excitation contraction
What is in the middle of the H zone?
The N line
What does the H zone do?
Holds the thick filament in place
What happens if the sarcomere shortens?
The whole cell shortens
What shape does the plasma Lamar make?
A cube - as it has right angle convolutions
Where do the T-tubular invaginations of the plasma lemma occur at?
Z lines
What do the 90 degree convolutions of the plasma lemma allow?
Allows the electrical citation to get deeper into teh cell to get closer to the sarcomeric units
What do the cardiomyocytes occur in?
They occur in unison, they occur in close proximity to the Z lines
What are the two structural specialisations of the cardiomycoyte?
Convolutions of the plasma lemma and the facilitation of CICR
Describe the facilitation of CICR in the cardiomyocytes?
Close positioning of the SR next to the t-tubule
What are the transverse T -tubules part of?
The Extracellualr part of the matrix
What is the double membrane system?
Developing from the T tubule cavity and SR
What determines the whole cell responsiveness?
Local spatiotemporal ca2+ dynamics
What does the local spatiotemporal ca2+ dynamics determine?
The whole cell cytosolic ca2+, nanometers localisation of CICR
Why do calcium sparks arise?
When the SR recognises that the ryanodine receptor 2 channels recognise the amount of ca2+ is too much, the ca2+ opens the channels and produces a ca2+ spark
What needs to happen in order for ca2+ to be released for the SR?
Dynamic equilibrium - is never 0 to is just at a lower level
How do Ca2+ sparks arise?
From spontaneous openings of protein channels on the SR membrane
How are ca2+ sparks at rest?
They occur spontaneously at rest
What are ryanodine receptors 2 sensitive to?
Sensitive to cytoplasmic ca2+ elevations and increases in SR luminal Ca2+
What techniques can look at ion currents?
Patch clamps experiments and configurations which can control the membrane potentials of the cell
Look up voltage L-type Ca current
What does an increase in frequency of ca2+ sparks mean?
More green, more spark, summation of ca2+ signals
What is the type of feedback loop of CICR?
Positive feedback loop and occurs at every t-tubule invagination at every Z line
What does each electrical action potential arriving at a cardiomyocytes lead to?
A rapid ca2+ rise across all individual sarcomeric units
What are the two main processes for return of ca2+ to rest?
Plasma lemma extrusion by Na+/Ca2+ exchange, re uptake to the SR by a ca2+ ATPase (SERCA)
What is SERCA regulated by?
By an accessory protein phospholamban
