Muscle 8 Flashcards
What does Excitation-contraction coupling describe?
The process that links the excitatory action potential to muscle contraction
Where does an action potential propagate in skeletal muscle?
The sarcolemma of the cell to the T-tubules
What happens once an action potential propagates along the T-tubule?
The triad depolarizes activating L-type Ca2+ channels in the T-tubule
Where are L-type calcium channels found?
Within the membrane of the T-tubules
How many L-type calcium channels are usually found together?
They are usually found in clusters of four
What do the L-type Ca2+ channels play a role in?
Voltage sensing by detecting depolarization
What is another name for the L-type Calcium channel?
DHP receptor
What are DHP receptors inhibited by?
DHP drugs
What happens once L-type calcium channels sense depolarization?
They open to allow Calcium into to cytoplasm of the muscle cell
What proteins are found within the membrane of the SR?
They Ryanodine Receptors aka Ca2+ release channels
What happens when Ryanodine receptors on the SR open?
They allow a large amount of calcium to exit from the sarcoplasmic reticulum into the cytosol of the muscle cell
Which direction do Ryanodine receptors face?
Towards the T-tubule
What do each of the Ryanodine receptors have?
An extension known as a foot process that connects to the L-type calcium channel
What happens once depolarization is sensed by L-type channels in T-tubles?
Some calcium exits the tubule and enters the cytoplasm and ryanodine receptor opens and calcium exits the sarcoplasmic reticulum and into the cytosol of the muscle cell
What acts as a voltage sensor in skeletal muscles?
L-type Ca2+ channels in the T-tubules
What is SERCA and what does it do?
An ATP dependant pump on the surface of the sarcoplasmic reticulum that removes calcium from the cytoplasm
What are the two ways that calcium can be removed?
It can be extruded across the plasma membrane or sequestered in intracellular compartments
What are the two ways that a cell might remove calcium from the intracellular space?
- Sodium calcium exchanger NCX
* Calcium pump PMCA
How does NCX work?
It extrudes one calcium ion from the cell in exchange for 3 sodium ions enter the cell
How does PMCA work?
Pumps calcium out of the cell using energy from the hydrolysis of ATP
In what muscle types are NCX and PMCA found in?
All muscle types
What is the most important mechanism for the cell to remove Calcium from the cytoplasm?
Calcium reuptake
What reuptakes calcium into the Sarcoplasmic reticulum?
SERCA
How does SERCA work?
Using the energy of ATP hydrolysis it pumps calcium into the sarcoplasmic reticulum
What buffers allow more calcium to be brought into the sarcoplasmic reticulum?
- Calsequestrin (skeletal/cardiac)
* Calreticulin (smooth)
How do Calsequestrin and Calreticulin work?
It keeps calcium levels low in the sarcoplasmic reticulum by binding to it in order to allow SERCA to continue working
