Flashcards in Smooth muscle innervation Deck (47)
What is the rough Em of smooth muscle cells?
Compare APs in smooth and skeletal muscle
Smooth - Slower upstroke and last longer
What current drives depol in SMC?
L Ca2+ current
What repolarises smooth muscle cells?
Ca2+ activated K+ channel and VGKC
Why is SM nerve transmission described as "en passant"
APs pass along neurone across each varicosity releasing neurotransmitter into synaptic cleft
How is visceral SM similar to SAN?
Can exhibit pacemaker activity
Describe what triggers contraction in single unit SM?
Pacemaker cells - spontaneous contraction.
Modified by ANS and neurotransmitters etc
Describe what triggers activation of multiunit SM?
Motor neurones (contraction initiated by neurotransmitter)
True of false, VGNC drives SM action potential?
False, it's Ca2+ (L type)
How do SM open SR (what mechanism)?
Intracellular signals, i.e. secondary messenger system
What are 3 mechanism for Ca2+ increase in SM?
Ligand gated ion channel
Ca2+ via L type channel (NA = agonist and depolarise cell membrane)
IP3 mediated Ca2+ release from SR
Instead of troponin, what initiates contraction in SM?
Myosin phosphorylated which activates its ATPase ability
Does SM need changes in Em for contraction?
What does tropomyosin do at rest?
Blocks myosin binding site, stabilises actin
What is functionally similar to troponin?
Caldesmon - regulates position of tropomyosin
Describe structure of myosin
2 heavy chains, 4 light chains head, hinge and tail region
Which part of myosin forms cross bridge with actin?
What part of myosin has ATPase activity?
In absence of Ca2+ what prevent actin myosin binding?
Myosin light chain (not tropomyosin)
True or false, tropomyosin stops actin myosin binding when Ca2+ absent (SM)?
False, it's Myosin light chain
How many Ca2+ bind to calmodulin?
What does Ca2+ bind to?
What 3 things does CalCam act on, what are the effects?
Activates MLCK - MLCK phosphorlylates P light chain of myosin (MLC)
CalCam acts on caldesmon removes inhibition of tropomyosin
Calcam binds to calponin -removes inhibiton on myosin head ATPase activity
Which part of myosin regulates cross bridge cycling?
P light chain
What happens after MLC phosphorylated?
Relieves MLC inhibition and ATP hydrolysed by myosin head and cross bridge cycling occurs
What happens in relaxation?
Dephos of MLC by MLCP when Ca2+ falls
What are the roles of PKA and PKG in smooth muscle relaxation on MLCK?
Phophorylate MLCK (inactive)
Reduce Ca2+ sensitivity of MLCK - more calcium calmodulin needed to activate it
How do PKA and PKG promote relaxation?
Phosphorylate K+ channel to hyperpolarise membrane inhibits Ca2+ entry
What are the roles of calponin and caldesmon (how do they compare to troponin/tropomyosin)?
Caldesmon (tropomyosin) and calponin (inhibits heads ATPase activity)