Physiology of smooth muscle Flashcards
What is different about the sarcoplasmic reticulum in smooth muscle when compared to that in skeletal muscle?
it is much less developed
How does smooth muscle get its calcium?
Through both the SR and ECF
Release of calcium from the SR utilizes what?
A Gq protein
When Gq proteins are activated what is produced?
IP3/DAG
What is the role of IP3/DAG?
it is a very strong stimulus of calcium to be released from the SR
How does smooth muscle get its Ca2+ from the ECF?
via calcium channels
Why does smooth muscle require Ca2+ from extracellular sources?
because smooth muscle has sustained contractions
At rest, what does the myosin head have associated with it?
ADP and Pi
What is different about the actin in smooth muscle when compared to the actin in skeletal muscle?
actin in smooth muscle does not have tropomyosin bound to it
What does a rise in intracellular Ca2+ cause?
it causes 4 calcium molecules to bind to 1 calmodulin molecule
What happens when calcium binds to calmodulin?
the calmodulin will activate myosin light chain kinase
what is the action of kinases?
kinases will add an inorganic phosphate to something
When the MLCK is activated what happens?
It adds an inorganic phosphate to the myosin light chain
What happens once the MLC is phosphorylated?
the myosin head has a higher affinity for the active site on the actin
How many inorganic phosphates will be associated with the myosin found in smooth muscle?
2
What happens when calcium leaves calmodulin and the MLCK is no longer activated?
a myosin light chain phosphorylase will remove the inorganic phosphate from the myosin light chain, and myosin will once again have a low affinity for the actin binding sites
What are two reasons why smooth muscle overall uses less ATP than skeletal muscle?
1) the isoform of the myosin that is found in smooth muscle is much slower than that found in skeletal muscle= less cycles per minute
2) the latch mechanism
What does the latch mechanism state?
at any given moment in time, the inorganic phosphate that is on the myosin light chain can be removed
if the inorganic phosphate is removed from the myosin light chain, what will happen?
The cross-bridge cycle will continue through the power stroke
What happens at the end of the power stroke, if the Pi has been removed from the myosin light chain?
the mysoin and actin will now have a low affinity for the ATP that is trying to bind. So it will take a long time for it to finally bind, which will then cause the myosin and actin to dissociate
Swellings in axon that function as the presynaptic terminal. Neurotransmitter is released from here
varicosity
What is nitric oxide made by?
endothelial cells
What is NO released into?
the space inbetween the endothelial cells and the smooth muscle
What is the role of NO?
it relaxes smooth muscle
