PHYS 1302 Lecture Notes - Lecture 11: Calmodulin, Signal Transduction, Stim1
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Smooth Muscle
● Smooth muscle must operate over a range of lengths
● Within an organ, the layers of smooth muscle may run in several directions
● Smooth muscles contract and relax much more slowly than skeletal/cardiac
muscle
● Smooth muscle uses less energy to generate and maintain a given amount of
force
● Smooth muscle can sustain contractions for extended periods without fatiguing
● Smooth muscles have small, spindle-shaped cells w/ a single nucleus
● Contraction in smooth muscle may be initiated by electrical or chemical signals or
both
● Smooth muscle is controlled by the ANS
● Smooth muscle lacks specialized receptor regions
● Ca2+ for contraction comes from the ECF as well as from the sarcoplasmic
reticulum
● Ca2+ initiates a cascade that ends w/ phosphorylation of myosin light chains and
activation of myosin ATPase
● Contractile cells are =,-$arranged in sarcomeres
○ Actin is much more plentiful in smooth muscle
○ Smooth muscle 2>1?0$-@,5,=A=
Myosin Phosphorylation Controls Contraction
1. An increase in cytosolic Ca2+ initiates contraction (Ca2+ released from both the
sarcoplasmic and ECF)
2. Ca2+ binds to !>2+,B/2A=$in cytosol
3. Ca2+ binding to Calmodulin is first step in a cascade that ends up in
phosphorylation of myosin light chains
a. Enhances myosin ATPase activity and results in contraction
Calcium Initiates Smooth Muscle Contraction
● Sarcoplasmic Ca2+ Release
○ SR release is mediated by @C>=,BA=3$@3135-,@$4DCD<$1>21A/+$@323>03$
1">==32 and by an )E9:@3135-,@$1">==32
○ SR release by RyR channel opening is called 1>21A/+:A=B/13B$1>21A/+$
@323>03$4!)!D<
○ IP3 channels open when GPCRs activate phospholipase C signal
transduction pathway
■ IP3 binds to SR’s IP3 channel to open and allow Ca2+ to flow out
○*F).%$protein sensor monitors Ca2+ stores in SR and if they decrease,
open to allow Ca2+ into the cell via active pumping
● Cell Membrane Ca2+ Entry
○Voltage-gated Ca2+ channels open in response to depolarization stimulus
○Ligand-gated Ca2+ channels open in response to ligand binding
○Stretch-activated channels allows cell to depolarize and neighboring
voltage-gated Ca2+ channels open in response
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Document Summary
Smooth muscle must operate over a range of lengths. Within an organ, the layers of smooth muscle may run in several directions. Smooth muscles contract and relax much more slowly than skeletal/cardiac muscle. Smooth muscle uses less energy to generate and maintain a given amount of force. Smooth muscle can sustain contractions for extended periods without fatiguing. Smooth muscles have small, spindle-shaped cells w/ a single nucleus. Contraction in smooth muscle may be initiated by electrical or chemical signals or both. Smooth muscle is controlled by the ans. Ca2+ for contraction comes from the ecf as well as from the sarcoplasmic reticulum. Ca2+ initiates a cascade that ends w/ phosphorylation of myosin light chains and activation of myosin atpase. Contractile cells are not arranged in sarcomeres. Actin is much more plentiful in smooth muscle. Sr release is mediated by ryanodsne receptor (ryr) calcsum release channel and by an ip3-receptor channel.
