Smooth muscle contraction Flashcards
What innervates smooth muscle?
ANS
What neurotransmitter can be release from post-ganglionic nerves onto smooth muscles from the PNS?
Acetylcholine (Ach)
What neurotransmitter can be released from post-ganglionic nerves onto smooth muscles from the Sympathetic NS?
Noradrenaline
What neurotransmitter can be released from post-ganglionic nerves onto smooth muscles from NANC (non-NA-non-Ach) nerves?
Nitric oxide (NO)
What hormone can be released from post-ganglionic autonomic nerves onto smooth cells from the adrenal medulla?
Adrenaline
How is smooth muscle contraction initiated?
By an increase in cytosolic Ca2+
How does an increase in cytosolic Ca2+ ?
- By influx from extracellular medium
- Release of Ca2+ from internal Ca2+ stores (from sarcoplasmic reticulum
What is calmodulin (CaM)?
A Ca binding protein
How does smooth muscle use a Ca2+- Calmodulin complex to generate a muscle contraction?
- Ca2+ binds to to calmodulin
- This Ca2+ and calmodulin complex activates the myosin light chain kinase (MLCK)
- MLCK phosphorylates light chains in myosin heads and increases myosin ATPase activity
- Actin myosin crossbridges slide along actin, creating muscle tension
In the absence of a rise in cytosolic Ca2+, what compound produces relaxation and how?
- Myosin light chain phosphatase
- Due to the myosin light chain being dephosphorylated, MLCP activity becomes dominated, leading to relaxation
How can cytosolic Ca2+ decrease?
- Ca2+ can be untaken into the SR- via Ca2+ ATPase
- Extrusion of Ca2+ from cell via Ca2+ ATPase and Na-Ca exchanger (1Ca+ moves out, 3Na+ move in)
How does stimulation of Gq mediated receptors produce a rise in intracellular Ca from voltage gated calcium channels?
- When a neurotransmitter binds to Gq protein receptors, it stimulates Na channels (ion channels) to open, causing depolarisation of the cell
- This creates an excitatory junctional depolarising potential, which, if reaches the threshold value of -40mV, activates the opening of VGCC
- This causes an influx of Ca2+
How does stimulation of Gq protein receptors cause the release of Ca2+ from internal Ca2+ stores in smooth muscle?
- Stimulation of Gq receptors causes Pip2 to be converted into IP3 and DAG via PLC.
- IP3 binds to IP3 receptors (these are ligand gated receptors) on the sarcoplasmic reticulum, which opens the ion channel, leading to an influx of Ca2+ down a concentration gradient, due to there being low Ca2+ in cytosol, and high in the SR