Smooth Muscle Physiology Flashcards
Do we see more actin in smooth muscle or skeletal muscle?
Much more actin in smooth muscle
(There is a lot more myosin in skeletal muscle)
Where does most of the calcium for contraction of a smooth muscle cell come from?
Outside the cell (not the sarcoplasmic reticulum)
What are the three methods for getting calcium out of a smooth muscle cell (that were covered in class)?
SERCA
Sodium / Calcium antiporters
Sarcolemmal Ca2+ ATPase
What does calcium bind to in smooth muscle cells to initiate a contraction?
Calmodulin
What is activated by Calmodulin after it binds to calcium?
Myosin light chain kinase
(Phosphorylates myosin light chains)
What are the functions of angiotensin II, vasopressin, and endothelin I?
They contract smooth muscle
What is the function of adenosine on smooth muscle?
Relaxes smooth muscle
What ion is primarily responsible for generating action potential in smooth muscle?
Calcium
What is different about the length tension curve between skeletal and smooth muscle?
Smooth muscle can adjust its length tension curve in order to maintain closer to the ideal.
histology:
Sk. M
Sm. M.
large, multi nucleated, striated cells
small, single nucleus, no striations
Sarcoplasmic reticulum
Sk. M.
Sm. M.
Sk. M: large, well developed, SR with triads, well developed T tubules
Sm. M: poorly developed SR, T tubules, membrane with caveoli
thin filaments
Sk. M
Sm. M
Sk. M actin, tropomyosin, tropinin
actin and tropomyosin
Thin filament number
Sk. m
Sm. M
fewer thin filaments in skeletal muscle than in smooth muscle
thick filaments
Sk. M
Sm. M
Sk. M. myosin, ATPase faster
Sm. M. myosin, ATPase slower, myosin light chain prominence
thick filament number
Sk. M.
Sm. M
Sk. M greater than in Sm, M
innervation
Sk. M
Sm. M
sk. M. a-motor neurons
Sm. M, multiple, intrinsic and autonomic nervous system
NTMs
Sk. M
Sm.M
Sk. M-ach, excititory
Sm. M-Ach, epi, NE, excite or inhibit
Transmission specialization
Sk. M
Sm. M
SK. M. NMJ
Sm. M. No NMJ, uses varicosties, no endplate specialization
NTM receptors
Sk. M
Sm. M
SK. M nicotinic cholinergic
Sm. M. muscarinic cholinergic, adrenergic, others
Other forms of activation
Sk. M
Sm. M
sk. M-none
Sm. M-blood borne, paracrine, intrinsic
ACtion potential
Sk. M
Sm. M
Sk. M-required
Sm. M-No, pacemaker activity, hormonal
Source of Ca
Sk. M
Sm. M
Sk. M-release from SR
Sm. M-release from SR and ECF influx
role of calcium
Sk. M
Sm. M
Sk. M-binds to troponin
Sm. M-binds to calmodulin, activates MLCK
Mechanism to alow actin and myosin binding
SK. M
Sm. M
Sk. M-tropomuposin moved by troponin
Sm. M-pi of myosin light chain
Relaxation
SK. M
Sm. M
Sk. M-removal of Ca from troponin
Sm. M-activation of light chain phosphatase, dephos.
describe multi-unit smooth muscle
fibers operate individually, innervated by a single nerve
ex: ciliary muscle of eye, iris, piloeretor muscle
Describe unitary smooth muscle
visceral smooth muscle that works as a unit
cell membranes adhere and contain gap junctions
ex: GI, bile ducts, uterus
In smooth muscle, what does actin attach to?
dense bodies/adherens junctions
describe smooth muscle contraction
cycling of myosin cross bridges is slower than SK. M.
the time myosin and actin are attached is greater which leads to a greater force while demanding less ATP
Describe the latch mechanims
as excitation in the smooth muscle slows, contraction remains
How does calcium enter the smooth muscle cell for contraction?
calcium enters cytosol via plasma membrane calcium channels
release from SR is minor
some comes in through ryanodine receptors or IP3 gates
Most calcium enters the smooth muscle cell via
sarcolemma-K type voltage gated Ca channels and receptor activated ca channels
CA leaves the cell via
SERCA
3Na/Ca antiporter
sarcolemma Ca ATPase
What does intracellular Ca bind to reversibly and what does that complex activate?
Ca binds reversible to calmodulin which activates MLCK which Pi the myosin head
contraction strength is generally proportional to Ca levels
Now actin and myosin can bind and contract the muscle
What does myosin light chain phosphatase do?
removes Pi group from MLC and along with calcium pumps to remove calcium ushers in the relaxation state of the smooth muscle
How does NE/Epi control SM. M?
adrenergic
excitatory (contract) via A1 receptors
inhibitory (relax) via B2 receptors
How does Ach control SM. M?
PSN
excitatory or inhibitory
contraction is a direct effect while relaxation is an indirect effect
How does angiotenin II, vasopressin and endothelin control smooth muscle?
How does adenosine and NO control smooth muscle?
Contract!
Relax!
What are some environmental cues of smooth muscle control and their effect?
hypoxia
excess Co2
increased H
adenosine, LA, increased K, etc
can call local dilation in vasculature sm.m.
what are spike potentials?
what are slow waves?
What are plateaus?
stimulated by hormones, NTMs, stretch and spontaneously
oscillating Ca influx and K efflux, have pacemaker capabilities
stimualted by NTMs, stretch
Describe the latch mechanism
it is a way to increase tension while decreasing ATP usage during Sm. M contraction
light chain gets dephoshp.
cycle proceeds slowly, and attached cross bridges are still generating tension (20-30%)
overall-increases time of contraction
