8/9 - Vascular Smooth Muscle Cells Flashcards
Contraction of smooth muscles can be _____ or ______
Contraction of smooth muscles can be tonic or phasic
What is tonic contraction?
- Tonic
- Slow and sustained contractions
- can maintain force for prolonged time with only little energy utilization
- eg respiratory, urinary tract, skin, eye and vasculature
- can maintain force for prolonged time with only little energy utilization
- Slow and sustained contractions
What is phasic contraction?
- Phasic
- Rapid contractions and relaxations
- eg digestive tract
- the phasic contraction of the smooth muscles in the GIT generates rhythmic peristaltic contractions
- eg digestive tract
- Rapid contractions and relaxations
Lable the three layers of the vasculature and the vascular smooth muscle cells
What is the tunica adventitia?
Outermost layer of vasculature
Contains some elastic fibres, collagen fibres and fibroblasts
What is the Tunica media?
Middle layer of vasculature
contains elastic fibres, collagen fibres, and smooth muscle
What is the tunica intima?
Innermost layer of the vasculature
Contains collagen and endothelial cells
What is the structure of vascular smooth muscle cells?
- Non-striated
- Spindle-shaped
- No sarcomere structure, but bundles of filaments
- Filament structures:
- dense bodies, actin, myosin filaments, intermediate filaments
- The contractile units are anchored to the dense bodies (rich in alpha-actinin)
- The intermediate-sized filaments (non-contractile) connect the dense bodies/contractile units (actin-myosin) to the cytoskeleton thereby synchronizing the contraction of the contractile units to generate whole cell contraction
What are the filament structures in vascular smooth muscle cells (4)
- dense bodies
- actin
- myosin filaments
- intermediate filaments
The contractile units of vascular smooth muscle cells are anchored to the _________ which are rich in ______
The contractile units of vascular smooth muscle cells are anchored to the dense bodies which are rich in alpha-actinin
What connects the dense bodies/contractile units (actin/myosin) to the cytoskeleton? What does this connection establish?
- intermediate-sized filaments (non-contractile) connect the dense bodies/contractile units (actin-myosin) to the cell cytoskeleton
- Connection synchronizes the contraction of the contractile units to generate whole-cell contraction
Dense bodies are rich in _______ and serve as cytoplasmic anchors for ________. they attach to _________ and connect them together
Dense bodies are rich in alpha-actinin and serve as cytoplasmic anchors for thin filaments (actin). they attach to intermediate filaments and connect them together
What are membrane adhesion complexes?
Junctions where actin filaments are connected to integrin proteins via “linker” proteins within the adhesion complexes such as alpha-actinin, talin, paxillin, vinculin, and filamin
Adhesion complexes of smooth muscle cells (SMC) are not static, they are _________ during contractile stimulation which triggers association of ________ with _________
Adhesion complexes of smooth muscle cells (SMC) are not static, they are dynamically regulated during contractile stimulation which triggers association of adhesion molecules with beta-integrins
What makes up the contractile unit of smooth muscle cells
- Thick filaments (15-18nm)
- predominantly myosin heavy chains (MHC)
- Myosin light chains (MLC)
- Thin filaments (6-8nm)
- Polymerized actin with tropomyosin attached to dense bodies
Intermediate filaments are predominantly ________ and ________
- Regulate ______ and ________ of SMCs
- Insert into _____ along with _____
- Facilitate ___________ that optimizes force generation
Intermediate filaments are predominantly vimentin and desmin
- Regulate shape and spatial organization of SMCs
- Insert into dense bodies along with actin
- Facilitate spatial reorganization that optimizes force generation
Thick filament (myosin II) is comprised of:
- 2 myosin heavy chains (MHC)
- globular head (N-terminus), neck and alpha-helical tail portion (c-terminus)
- 4 Myosin light chains (MLC)
- 2 essential light chains (ELC) contribute to structural stability of myosin head
- 2 regulatory light chains (RLC) contain activating/inhibitory phosphorylation sites
What are the structural components of thin (actin) filament
- thin (actin) filament is comprised of
- alpha-actin
- tropomyosin
- calponin
- caldesmon
_______ is the primary form of actin in smooth muscle cells
alpha-actin is the primary form of actin in smooth muscle cells
Tropomyosin expands over __________
Tropomyosin expands over 7 actin monomers (function in SMC unknown)
SMC do NOT have the ______ (unlike cardiomyocyte and skeletal muscle)
SMC do NOT have the troponin complex (unlike cardiomyocyte and skeletal muscle)
Instead of troponin what do SMC have?
Instead of Tn, SMC have calponin and caldesmon
_______, ______ and ______ inhibit the ATPase activity of the myosin complex that otherwise provides energy for SMC contraction
Tropomyosin, calponin and caldesmon inhibit the ATPase activity of the myosin complex that otherwise provides energy for SMC contraction
What is calponin?
- A load-bearing 32kDa protein
- inhibits the ATPase activity of myosin
- interacts with actin monomer at a distinct site between CH and CaP in a 1:1 ratio
CH = calponin homology domain
CaP = calponin repeats