B1W3: Smooth Muscle Flashcards
Single Unit Smooth Muscle
Synctium
Joined via gap junctions
Spontaneous activity
i.e visceral walls, smaller blood vessels
Multi-unit smooth muscle
Separate muscle fibers, each innervated by own ending
Each fiber contracts independently
Stimulated by nerve signals
i.e. aorta
Smooth muscle properties
- no striations/sarcomeres
- troponin absent
- Filaments attach to dense bodies
- thick filament regulation
Thick filament
Myosin
Ca2+ regulation due to its phosphorylation
ATP switch
What filament does smooth muscle have more of?
Thin filaments
Contractile mechanism of smooth muscle
Ca2+ binds to calmodulin
Calmodulin binds to MLCK
MLCK phosphorylates light chain of myosin
ATP activity works
What initiates contraction in smooth muscle?
Calcium
Regulation at thick filament, rather than thin (in skeletal muscle)
What is speed of contraction based on in smooth muscle?
Myosin light chain kinase activity
i.e. smooth muscle contraction cycling…MUCH slower than skeletal muscle
Increased phosphorylation=increased speed
Why does smooth muscle have prolongued tonic contractions but use less energy?
Force can be maintained with decreased phosphorylation (ie less MLCK activity) to conserve energy (i.e. latch state)
Excitation/Contraction Coupling in Smooth Muscle
Depolarization opens voltage gated Ca2+ channels
Gets Ca2+ from ECF, ligand-gated Ca2+ channels, IP3 gated channels on SR, Ca2+-induced-Ca2+ release from SR
–SR not extensive, high surface area to volume ratio allows easy flow of Ca2+ to most of cell unlike skeletal
Why is smooth muscle resting membrane potential less negative than skeletal muscle?
Lower gk
T or F: there are fast Na+ channels in smooth muscle
False, there are none!
How can, through pharmacomechanical coupling, you increase the force of smooth muscle without changing membrane potential?
Increased sensitivity to Ca2+ (increase MLCK activity)
IP3 induced Ca2+ release (when GPCR Gq is engaged, PIP2 is split into DAG and IP3, IP3 opens Ca2+ channels in SR)
Can smooth muscles shorten less or more than skeletal muscle?
More due to criss-cross linkages
This leads to a wider length-force curve because it is able to contract with more force from a wider range of lengths
current carrying ion in smooth muscle
Ca2+
