Smooth Muscle Flashcards
Structure of smooth muscle
No t-tubules, irregular arrangement of myofilaments, one nucleus
Sympathetic nerve releases?
Noradrenaline
In Smooth muscle contraction and artery narrowing what receptor is involved? , and state process
Alpha 1 adrenoreceptor, gaq linked
- PLC hydrolyses PIP2
- breaks down to IP3 and DAG
- IP3 = increased calcium release
- DAG = increased calcium influx
Leads to Smooth muscle contraction and artery narrowing
Calmodulin
Calcium sensor in smooth muscle cells
Difference between skeletal/cardiac muscle in interaction with myosin to smooth muscle
Skeletal/cardiac = removal of a suppressive element (tropomyosin)
Smooth = activation of myosin
Myosin is smooth muscle is a different ….. To skeletal?
Isoform
Smooth muscle isoform
MYH11
Why does smooth muscle myosin at rest, has a lower ATPase activity?
No need for ATP hydrolysis to change shape of myosin ( power stroke)
Why does smooth muscle myosin at rest, has a lower affinity for ATP?
Need binding of ATP to allow detachment of myosin from actin molecule
Activated MLCK does what?
Phosphorylates regulatory MLC (myosin light chain) at ser 19 , activating it
- increases ATPase activity of myosin (about 1000 folds)
MLCP
Myosin light chain phosphatase
What does MLCP do?
- phosphatase removes phosphate groups - reduces activity when calcium goes down
What type of mechanism is MLCP
Off mechanism
What inhibits MLCK?
Protein kinase A
Effect PKA increase on smooth muscle cell vs cardiac muscle cell
In cardiac muscle cell, PKA increase does not affect contraction process
In smooth muscle it causes it to relax as PKA inhibits MLCK
