2017 Physiology - Smooth Muscle Flashcards
What are 2 proteins that make up the intermediate filaments of smooth muscle?
Desmin and Vimentin
What protein are in dense bodies and what do they correspond to in striated (skeletal) muscle?
Actinin
Functionally analogous to Z-lines, serve as anchor for thin-filaments (Actin)
Does smooth muscle have terminal cisterns or T-tubules?
No
How many light and heavy subunits does smooth muscle myosin have?
6 total
- 2 heavy
- 4 light
Describe the innervation and communication between Single Unit smooth muscle cells?
Many gap junctions
Sparse innervation - no true neuromuscular junctions, instead nerves just “drop” NT on smooth muscles
Muscle behaves in a syncytial manner
Describe the innervation and communication between Multi Unit smooth muscle cells?
Tend to be more discrete activities
Fewer gap junctions
Higher Innervation ratios
-graded potentials but no real action potentials
What modifications take place around pregnancy in smooth muscle, specifically progesterone and estrogen.
Progesterone - reduce gap junctions in myometrial smooth muscle, behaves more like non-innervated multiunit smooth muscle
Estrogen - at term, smooth muscle hypertrophy, increase gap junctions - behaves more like single unit
What is the role of the Ca++/Calmodulin complex?
Binds to Myosin Light Chain Kinase (MLCK) and activates it forming an enzyme complex.
What is the function of the MLCK/Ca++ Calmodulin complex? What are the energy requirements?
Phyosphorylates the myosin light chains, requiring 1 ATP
What is the function of Myosin Light Chain Phosphatase (Phosphatase C)?
removes phosphates put on myosin light chains by MLCK/Ca++ Calmodulin complex
What is the energy requirement for cross-bridge cycling in smooth muscle?
1 ATP
What is the purpose of the latch state and how does it work with smooth muscle?
Latch state is similar to rigor in skeletal muscle, it allows maintained contraction without ATP expenditure.
The myosin light chains are de-phosphorylated and ATPase activity thus decreases.
What factors contribute to smooth muscle relaxation?
low levels of phosphorylated myosin light chains
lowering of intracellular [Ca++]
How is Ca++ removed from smooth muscle cells?
Sequestered by sarcolemmal 3Na/Ca exchanger and Sarcolemmal Ca++ ATPase.
Phosphorylation of Phospholamban (which normally inhibits SR Ca++ ATPase) by PKA/PKG
How many types of Ca++ channels and describe them?
L-type (slow) - long acting, open slowly and close slowly. Affected by Ca-channel blockers such as verapamil, nifedipine, diltiazem
T-type (transitent) - fast acting, may be key to Ca++ induced Ca++ release from SR which is sensitive to relative change in concentration not absolute concentration. NOT blocked by typical Ca++ channel blockers.
