Intro to Smooth Muscle Flashcards Preview

Module 3 > Intro to Smooth Muscle > Flashcards

Flashcards in Intro to Smooth Muscle Deck (14):
1

Peripheral Resistance equation

(8 x μ* x Length )÷ r^4


*viscosity

2

Contraction of VSMCs

- Pull inwards to shorten around the vessel they surround

- As they shorten, the get thicker (conserving their volume) and pucker out in places

- Can easily shorten to 50% their length

3

Morphology, Arrangement of VSMCs

- Thin, spindle-shaped cells

- Arranged side by side

- May wrap around the vessel many times in smallest
arterioles

4

Structure of VSMCs

- Contractile apparatus is connected to the membrane to ensure contraction is translated

- Actin filaments are attached to membrane associated desmosomal bodies (DB) and dense bodies (= to z-lines)

- Caveoli invaginations to aid in EC coupling

5

The SR 1

- Small (1-7.5% of cell volume)

- Poorly coupled to outer plasma membrane

- Contains Ca, buffered by calreticulin and calsequestrin

6

SR channels/receptors and regulation of SR Ca Uptake

Ca Uptake
- SERCA2b/3
reg by PL*
inhb by thapsigargin/cyclopiazonic acid


Ca release
- IP3R
- RyR

(PL reg by cA/GMPK)

7

The SR Ca release channels

RyR

- CAICAR?
- Not much known
- May contribute to same process as IP3R

IP3R

- Ligand activated
- Sparks
- Ca waves propagate through cells
- Ion channel and TF regulation

8

VSMC Structure 2 ('cytoskeletal' connection)

- Quasi-myofibrils run longitudinally

- Intermediate filaments run laterally, connecting the dense bodies to one another

9

Force Production in VSMCs compared to CMs (LTR and CBC)

Length-Tension R
- Can exert force over a wide range of length
- Can shorten far more than CMs (50% vs 15%)

Cross-bridge Cycle
- Cycle of motor is the same as in CMs
- Release of Pi/ADP (rate-limiting) is much slower
- Force-generating fraction of the cycle is ~30%, only 5% in cardiac muscle

10

EC Coupling in VSMCs

-Cells must maintain steady tension at precise level, have varying dependence on these two systems

Electromechanical

Pharmacomechanical
- Vasoconstrictor agonist to GPCR has two actions:
1. Open Ca channels
2. Activate phospholipase C, IP3 from PIP2, IP3 on IP3R to cause CAICAR

11

VSMC vs CM Structure,
Appearance

- Both have elements running along (z-lines or dense bodies)

Appearance
- No physically defined sarcomere in VSMC
- VSMC smaller and thinner

12

Myosin

- VSMC myosin more similar to that of non-muscle motile system myosin than CM myosin

Side-polar myosin
- My. tails in anti-parallel arrangement
- Bars of cross-bridges in opposite direction on each side
- Dense bodies (with actin) interdigitate on both sides

13

Role/Expression of SMCs in vasculature

- Varies TPR by altering radius
- Maintains vascular tone
- Maintains circumference in high pulse-pressure arteries
- Most in arterioles and muscular arteries, some in aorta
- Veins/venules have less but can alter diameter greatly due to the low pressure in the venous system

14

Ca Regulation of Contraction

Primary Pathway:
Ca binds calmodulin -> activates MLCK* -> activates myosin

Secondary Pathway:
Ca binds CaBP -> CaBP relieves caldesmon inhibition of myosin

*also activated by MAPK