copyright © 2007 pearson education, inc., publishing as benjamin cummings twitch time course...
TRANSCRIPT
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Twitch time course
Duration of twitch is largely governed by rate of sequestration of calcium into SR
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
X-ray crystal structures
In the beginning of the movie, the myosin heads are in the prestroke ADP-Pi state (yellow) and the
catalytic cores bind weakly to actin. Once a head docks properly onto an actin subunit (green),
phosphate (Pi) is released from the active site. Phosphate release increases the affinity of the
myosin head for actin and swings the converter/lever arm to the poststroke, ADP state
(transition from yellow to red). The swing of the lever arm moves the actin filament by ~100 Å; the exact distance may vary from cycle to cycle depending
upon the initial prestroke binding configuration of the myosin on actin. After completing the stroke, ADP
dissociates and ATP binds to the empty active site, which causes the catalytic core to detach from actin.
The lever arm then recocks back to its prestroke state (transition from red to yellow).
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-13
Phosphocreatine
Provides ATP at beginning of exercise needed for contraction
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Muscle Fatigue
Locations and possible causes of muscle fatigue
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Muscle Fiber Types
Fast-twitch glycolytic and slow-twitch oxidative muscle fibers
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Length-Tension Relationships in Contracting Muscle
Figure 12-16
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Summation of Contractions
Figure 12-17a
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Summation of Contractions
Figure 12-17b
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Summation of Contractions
Figure 12-17d
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Isotonic and Isometric Contractions
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Series Elastic Elements in Muscle
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Muscle Contraction
Duration of muscle contraction of the three types of muscle
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-25a
Types of Smooth Muscle
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Types of Smooth Muscle
Figure 12-25b
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Smooth Muscle
Has longer actin and myosin filaments
Myosin ATPase activity much slower
Actin more plentiful
Has less sarcoplasmic reticulum IP3-receptor channel is the primary calcium channel
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Anatomy of Smooth Muscle
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-28, step 1
Smooth Muscle Contraction
ECF
Ca2+Ca2+
Sarcoplasmicreticulum Intracellular Ca2+
concentrations increase when Ca2+ enters cell and is released from sarcoplasmic reticulum.
Ca2+
11
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-28, steps 1–2
Smooth Muscle Contraction
ECF
Ca2+Ca2+
Ca2+
Sarcoplasmicreticulum
CaM Pi
Pi
CaM
Intracellular Ca2+
concentrations increase when Ca2+ enters cell and is released from sarcoplasmic reticulum.
Ca2+ binds to calmodulin (CaM).
Ca2+
1
2
1
2
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-28, steps 1–3
Smooth Muscle Contraction
ECF
Ca2+Ca2+
Ca2+
Sarcoplasmicreticulum
CaM Pi
Pi
ActiveMLCK
CaM
Intracellular Ca2+
concentrations increase when Ca2+ enters cell and is released from sarcoplasmic reticulum.
Ca2+ binds to calmodulin (CaM).
Ca2+–calmodulin activates myosin lightchain kinase (MLCK).
Ca2+
InactiveMLCK
1
2
3
1
2
3
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-28, steps 1–4
Smooth Muscle Contraction
ECF
Ca2+Ca2+
Ca2+
Sarcoplasmicreticulum
CaM Pi
Pi
ActiveMLCK
CaM
ADP +
Active myosinATPase
PP
Intracellular Ca2+
concentrations increase when Ca2+ enters cell and is released from sarcoplasmic reticulum.
Ca2+ binds to calmodulin (CaM).
Ca2+–calmodulin activates myosin lightchain kinase (MLCK).
MLCK phosphorylates light chains in myosinheads and increases myosin ATPase activity.
ATP
Ca2+
Inactive myosin
InactiveMLCK
1
2
3
4
1
2
3
4
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-28, steps 1–5
Smooth Muscle Contraction
ECF
Ca2+Ca2+
Ca2+
Sarcoplasmicreticulum
CaM Pi
Pi
ActiveMLCK
CaM
ADP +
Active myosinATPase
Actin
PP
Intracellular Ca2+
concentrations increase when Ca2+ enters cell and is released from sarcoplasmic reticulum.
Ca2+ binds to calmodulin (CaM).
Ca2+–calmodulin activates myosin lightchain kinase (MLCK).
MLCK phosphorylates light chains in myosinheads and increases myosin ATPase activity.
Active myosin crossbridges slide along actin and create muscle tension.
ATP
Increasedmuscletension
Ca2+
Inactive myosin
InactiveMLCK
1
2
3
4
5
1
2
3
4
5
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-29, step 1
Relaxation in Smooth MuscleCa2+
ECFCa2+
Ca2+Ca2+
Na+
Na+
Sarcoplasmicreticulum
Free Ca2+ in cytosol decreases whenCa2+ is pumped out of the cell or backinto the sarcoplasmic reticulum.
1
1
ATP
ATP
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-29, steps 1–2
Relaxation in Smooth MuscleCa2+
ECFCa2+
Ca2+Ca2+
Ca2+
Na+
Na+
CaM
CaM
Sarcoplasmicreticulum
Free Ca2+ in cytosol decreases whenCa2+ is pumped out of the cell or backinto the sarcoplasmic reticulum.
Ca2+ unbinds from calmodulin (CaM).
1
2
1
2
ATP
ATP
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-29, steps 1–3
Relaxation in Smooth MuscleCa2+
ECFCa2+
Ca2+Ca2+
Ca2+
Na+
Na+
CaM
CaM
Inactive myosin Myosin ATPaseactivity decreases.
ADP +
Myosinphosphatase
PP
ATP
Sarcoplasmicreticulum
Free Ca2+ in cytosol decreases whenCa2+ is pumped out of the cell or backinto the sarcoplasmic reticulum.
Ca2+ unbinds from calmodulin (CaM).
Myosin phosphatase removes phosphate from myosin, which decreases myosin ATPase activity.
1
2
3
1
2
3
ATP
ATP
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-29, steps 1–4
Relaxation in Smooth MuscleCa2+
ECFCa2+
Ca2+Ca2+
Ca2+
Na+
Na+
CaM
CaM
Inactive myosin Myosin ATPaseactivity decreases.
ADP +
Myosinphosphatase
PP
ATP
Decreasedmuscletension
Sarcoplasmicreticulum
Free Ca2+ in cytosol decreases whenCa2+ is pumped out of the cell or backinto the sarcoplasmic reticulum.
Ca2+ unbinds from calmodulin (CaM).
Myosin phosphatase removes phosphate from myosin, which decreases myosin ATPase activity.
Less myosin ATPase results in decreased muscle tension.
1
2
3
4
1
2
3
4
ATP
ATP
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-30
Control of Smooth Muscle Contraction
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Smooth Muscle
Smooth muscle cells contain stretch-activated calcium channels Open when pressure or other force distorts cell
membrane
Known as myogenic contraction
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Membrane Potentials Vary in Smooth Muscle
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Membrane Potentials Vary in Smooth Muscle
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Membrane Potentials Vary in Smooth Muscle
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Smooth Muscle Regulation
Many smooth muscles have dual innervation Controlled by both sympathetic and parasympathetic
neurons
Hormones and paracrines also control smooth muscle contraction Histamine constricts smooth muscle of airways