Smooth Muscle Flashcards
What does myosin light chanin Phosphotase (MLCP) do ?
removes phosphates from myosin necks inhibiting its action
When Ca++ binds with Calmodulin making a Ca++/CAM complex it then:
*#1: Inhibits calponin and caldesmen which moves tropomyosin out of the way exposing the G sites and allows cleavage of ATP by the myosin head
*#2: Activates MLCK (myosin light chain kinase) which adds a phosphate to the myosin neck activating ATPase cleaving ATP and cocking the head
What does Myosin light chain kinase (MLCK) do?
Once activated by the Ca++ calmodulin complex it phosphorylates the light chain of myosin thus activating myosin
What does Myosin light chain phosphatase (MLCP) do?
dephosphorylates myosin initiating relaxation
What does the Gq (GPCR) receptor do in smooth muscle?
*#1: Activates IP3 which acts as a second messenger to release stored calcium
*#2: activates Rho-kinase which inactivates MLCP inhibiting relaxation
What does the Gs (GPCR) receptor do in smooth muscle?
stimulates cAMP release which decreases activation of MLCK inhibiting contraction
What does the Gi (GPCR) receptor do in smooth muscle?
inhibits cAMP release which decreases activation of MLCK. less inhibition means more contraction!
Nitric oxide increases cGMP. What does this do?
Activates MLCP which initiates muscle relaxation
How many calcium are needed to activate Calcium calmodulin complex?
4
Smooth Muscle size:
1 - 5 mocrometers in diameter
20 - 500 mocrometers in length
Multi-Unit smooth muscle:
“fine control”
fibers seperated from eachother by basement membrane (cilliary, iris of eye, piloerector, tunica media?, large airways?)
Unitary smooth muscle:
MANY fibers contract as ONE
sheet/bundles
gap junctions
(GI, Bile ducts, Ureters, uterus, blood vessels)
What are Dense Bodies?
“the Z disks of smooth muscle”
actin attachments
attach to cell membrane
inter-cellular protein bridges
Smooth mucle nerves:
Autonomic neruon varicosity
diffuse junctions
secret NTs diffusely into cell
no direct innervation
(ACh & Norepinephrine)
The regulatory chain (one of the lght chains) of myosin is phosphorylated in response to what?
Activation of myosin light chain kinase (MLCK)
What are Caveolae?
Possibly underedveloped version of a T-tubule
(invaginations on cell membrane)
What is the mitigating factor in smooth mucle contraction?
Calcium concentration in the ECF
What happens when Ca++ levels drop in the cytosol?
*1: Ca++ is released from calmodulin
*2: Myosin phosphatase removes phosphate from myosin light chain (rendering in inactive) causing detachemtn of mysoin head from actin
What controls smooth muscle contraction
Nervous signals
Hormonal stimulation
muslce stretch
chemiclas
Latch Mechanism
Prolongs contraction with little energy use (can be hours)
Stress-Relaxation Mechanism
hollow organs maintain same amount of pressure despite large volume changes
Smooth muscle membrane potential:
usually -50 to -60mV
What is smooth muscle latent period?
time requried for diffusion oc CA++ from ECF to ICF (200-300 miliseconds) (50x longer than in skeletal muscle)
How much less energy is needed than in skeletal muscle:
1/10 - 1/300 of energy needed to sustain tension of contraction
Total time of contraction
1-3 seconds (30x skeletal muscle)
Is force of contraction less or greater than in skeletal muscle
Greater force of contraction
Action potentials in unitary muscle are usually:
Spiked or plateau
What % of smooth mucle contraction is not caused by APs?
50%
Local feedback mechanisms that will cause VASODILATION
Lack of O2
Excess CO2
Increased H+
