theme 1 : Smooth Muscle Cells structure CML

What are the two types of smooth muscle cells?

Multi-unit smooth muscles → autonomic neuron varicosity surrounding each CML (so independent)

each cell must receive a signal

noradrenaline from orthosympathetic nervous system

acetylcholine from parasympathetic system

unitary smooth muscles → gap junctions between CML so they are all connected

one activation activates all of them

what does a sarcomere look like

z = point d'ancrage de filament d'actine

M = support filament eppais mysosine

what is observed in a CML under micrscopy

mitochondria

Dense body db → corps dense aux e- → zone d'ancrage des filaments fins active

dense plate dp → plaque dense aux e-

sarcoplasmique reticulum

caveaola

microtubules

What is the role of dense bodies in smooth muscle cells?

Dense bodies anchor thin filaments in smooth muscle cells and the thick filament stays in between the 2 thin filaments held by dense body

what are the 6 isoforms of actin

contractile :

- skeletal alpha actin

- cardiac alpha actin

- smooth muscle alpha actin

- smooth intestinal gamma actin

cytoskeletal :

- cytosolic gamma actin

- beta actin (in all cells)

what are the contractile filaments of CML

heavy filament : myosin filament + myosin heads

light filament : smooth muscle alpha actin + tropomyosin + caldesmon + calponin

role of tropomyosin

stabilise actin filament and can be homo/heterodimer

role of caldesmon and calponin

inhibitor effector and stabilises actin filament

when bound to calcium and therefore phosphorylated it becomes inactive

what are the two important myosin light chains

MLC20 and MLC17 = central point of contraction of CML depending on phosphorylation

what are the two states myosin light chains (MLC) in smooth muscle contraction?

Inactivated : dephosphorylated and folded conformation (MLC20) and cant bind to actin filament

Activated : MLC20 phosphorylated and becomes linear to bond w/ actin filament -> contraction

how is the phosphorylation of MLC induced

Cytosolic Ca2+ bind with calmodulin

MLC20 interacts w/ Ca-CaM + ATP

MLC20 is phosphorylated -> dimerisation -> contraction

how are the contractile units organised

Functional units (db) = filament fin + eppais qui permet le déplacement physique entre 2 corps dense ou 1 corps dense et 1 corps d'attachement

Plaque d'attachement = filament fin s'attache ici

intermediate filaments = relié les corps dense et permet de maintenir les corps dense dans l'éspace

what occurs to the contractile units during a contraction

the functional units come closer to each-other

contraction de toutes les sense

what are the main regulations of excitation-contraction coupling

local/paracrine

hormonal via blood with through the vasovasorum

nervous -> ortho(maj)/parasympathetic

What are the two types of smooth muscle activity patterns?

Tonic smooth muscles (sustained contraction) and phasic smooth muscles (rhythmic contraction).

what are the mechanisms are involved in excitation-contraction coupling

stimulating ligand that activates a 7 domaine TM coupled to a G protein and RTK enzymatic receptor

voltage dependant channel

stretch activated channel

what are the two types of PA in CML

slow depolarisation waves : parallel PA rapid after passing threshold

spike potential : spikes of PA

PA in CML of Iris arteriole

membrane potentiel = -40 mv

during each PA the diametre of the blood vessel decreases -> contraction

PA of CML in basilar artery

membrane potentiel = -40mv

during each PA diametre increases -> relaxation

what ions enter and leave during a PA

initail depolarisation to reach threshold : exit of Cl-1

once threshold passed theres a depolarisation : calcium channels voltage dependent open and let the entry of calcium

repolarisation : potassium channels are responsible for the exit of K+

membrane potentiel of a CML

-50mv

what are the calcium channels involved in Ca entry

L and T type channels

activity of potassium channels during hyper/depolarisation

Ca channels voltage dependent closed -> K+ channels open and exit CML -> hyperpolarisation -> vasodilation

Ca channels voltage dependent open -> high + charge inside cell -> K+ channels closed -> no K+ exit -> depolarisation -> vasoconstriction

role of potassium channels

maintain resting potential

when are chlore channels activated ?

local increase of intracellular calcium

increase in cell volume

activity of chlore channels during hyper and depolarisation

Ca voltage dependent channels closed -> Cl channels closed -> (-) charge accumulation -> hyperpolarisation -> vasodilation

Ca voltage dependent channels open -> Cl channels open -> exit of Cl- and increases + charge inside cell -> threshold reached -> depolarisation -> vasoconstriction

What are ionotropic receptors?

Receptors that mediate fast synaptic transmission by allowing ions to flow through their channels.

how does noradrenaline/ATP and purinergic(ATP) ionotropic receptors P2X increase intracellular Ca

co-liberation of ATP and noradrenaline by a nerve cell -> ATP binds to purinergic receptors that allow entry of Ca and Na -> purinergic Ca transient -> depolarisation -> activates voltage dependent calcium channels -> increase of intracellular Ca

how can mechanical stress depolarise the ell

mechanical stress -> stretch dependent cation channels SAC are activated -> entry of Ca and Na -> depolarisation

what is the cellular signalling process when mechanical stress activates stretch dependent cation channels

mechanical stress will activate the SAC -> opening of the channel -> entry of Ca into the CML -> Ca-CaM -> MLC phosphorylation -> contraction

What is calcium-induced calcium release (CICR) in smooth muscle cells?

A mechanism where calcium influx triggers further calcium release from the sarcoplasmic reticulum.

Calcium Induced Calcium Release CICR works how ?

L type Ca channels/Ionotropic receptora and SAC are activated -> entry of Ca -> Ca inds to RYR2/3-> stocked Ca leaves sarcoplasmic reticulum SR (-> leaved cell thanks to ATP and enters SR by Ca ATPase SERCA)

do CML have a lot of Ca reserve in sarcoplasmic reticulum compared to CMStrié

no they have less Ca stockage

What is pharmacomechanical coupling?

A process where chemical signals (like hormones) induce muscle contraction through calcium signaling without direct electrical stimulation.

What is L'IP3-induced calcium release?

A pathway where inositol trisphosphate (IP3) stimulates the release of calcium from the endoplasmic reticulum

how does IP3 induce calcium release

ANGII binds to RCPG -> PLC activated -> acts on PIP2 -> DAG + IP3 -> IP3 binds to RIP3 on sarcoplasmic reticulum membrane -> Ca release

what protein g is involved in ANGII recognition and PLC activation

Gq11

What is the function of IP3 in smooth muscle cells?

It induces calcium release from the sarcoplasmic reticulum as a second messenger

what are the main store operated channels SOC and what are they activated by

TRPC 1,4 and 5

activated by the decrease of Ca in SR

What is capacitative calcium entry?

A process by which calcium enters the cell after depletion of calcium stores in the endoplasmic reticulum carried by TRPC 1,4,5 (SOC)

what are main second messenger operated channel SMOC/ROC and what are they operated by

TRPC 3,6 and 7

activated par DAG

how do SOC (TRPC 1,4,5) increase Ca entry into cytoplasm

when SR is depleted from Ca -> oligomerisation of STIM1/2 -> STIM and TRPC interact -> Ca entry into cytoplasm

how do SMOC (TRPC 3,6,7) increase Ca entry into cytoplasm

DAG (produced with IP3 from activity of PLC on PIP2) binds to TRP 1,4,5 -> SOC opens -> Ca entry

what is kinase that phosphorylates MLC to induce contraction

MLCK

how is MLCK (kinase for MLC) activated

when Ca-CaM complex binds to MLCK

what de-phosphorylates MLC

MLCP = MLC phosphatase

what happens to the contractile force and intracellular calcium variation in mous aorta after stimulation

stimulation -> elevation of Ca -> then decrease of intracellular Ca which continues to decrease

stimulation -> increase of contractile force -> plateau (even when Ca decreases) -> slight increase when Ca continues to decrease

if intracellular Ca continues to decrease but contractile force increases (slightly) what does it mean

Ca induces contraction but there is a contractile apparatus sensitivity to calcium

what happens to contraction when agonist noradenaline is added

vessel permeability increases so increased entry of Ca

more sensitive to Ca -> increased contractile response

what mechanism is involved with contractile apparatus sensitivity to Ca

RhoA/Rho kinase

what are Rho proteins

monomeric G proteins that exchanges GDP and GTP

how is Rho activated

a exchange factor exchanges GDP on Rho to GTP

what is the role of activated Rho

activated GTP-Rho activates Rho kinase

activates GTPase GAP to degrade GTP (slow process) to return to OFF state of Rho

what complex can maintain the OFF activity of Rho

GDI (partner protein) binds to Rho-GDP and maintains its inactivity

what does RhoK (kinase) inhibit to maintain contracted state

MLCP = phosphatase

MLC20 remains in phosphorylated state longer

how does RhoK (when activated by GTP-Rho (by GEFs)) act on the contraction

Rho kinase phosphorylates :

- CPI 17 -> inhibiting activity of MLCP -> no dephosphorylation of MLC20

- MLCP -> remains in inactive form -> no dephosphorylation of MLC20

- MLC20 -> contraction

what is the CML contraction-relaxation cycle

Increase of intracellular Ca -> Ca + CaM -> Ca-CaM + MLCK -> +ATP -> MLC phosphorylation -> phosphoMLC + actine -> phospho-actomyosine -> contraction

RhoA-GDP -> GEFs -> RhoA-GTP (active) -> Rho kinase -> inhibit MLCP (directly by phodpho or indirectly by CPI17 phospho) -> phosphoMLC -> contraction

so overall what are the processes involved in excitation-contraction coupling in CML

L type CA channel/ionotropic receptors/SAC -> entry of Ca

ANGII binds to RCPG (type Gq11) -> PLC -> PIP2 -> IP3 + DAG

IP3 -> binds to RIP3 -> Ca exit of sarcoplasmic reticulum

DAG -> binds to SMOC -> Ca entry into cyoplasm

Ca binds to RYR2/3 on SR -> exit of Ca of SR

Ca activates MLCK -> phospho MLC20 -> contraction

ANGII binds to RCPG (Gq11) -> activates GEFs -> RhoA-GTP -> Rho Kinase -> inhibits MLCP -> contraction

what is passive relaxation of CML

inactivation/stopping of excitation-contraction mechanisms to make exit Ca from cytoplasm or enter SR (stockage)

what ATPase/pumps/exchangers are involved in passive relaxation

SERCA (SR Ca ATPase)

PMCAs (plasma membrane Ca ATPase)

Na/ CA exchangers

mitochondria

how does Na/Ca exchanger act

for one Ca2+ that leaves the cell 3 Na+

how does PMCA and SERCA work

Mg enters and Ca leaves (ATP) the cytoplasm -- PMCA

Mg leaves RS and Ca enters (+ATP) -- SERCA

what is active relaxation

where a signal/molecules acts on the CML to induce relaxation

What factors can lead to vasodilation in smooth muscle cells?

BNP,CNP,ANP and neuronal nitric oxide (NO).

how does A/B/CNP act on relaxation

they bind to receptors w/ enzymatic activity (guanylate cyclase)

- sGC -> cGMP -> PKG (relaxation)

What are the effects of nitric oxide (NO) on smooth muscle?

NO diffuses across membrane and induces vasodilation by increasing cGMP levels, which activates MLCP and promotes relaxation.

what is the activity of PKG

kinase that phosphorylates & inactivate contractile actors or activate relaxing factors

how does PKG act in active relaxation

when activated by cGMP -> PKG acts on :

- inhibiting IP3 mediated pathway

- increase entry of Ca into SR

- decrease intracellular Ca -> decreased activity of MLCK -> myosin head detaches from actin -> relaxation

- inhibits RhoA

What is the role of cyclic guanosine monophosphate (cGMP) in smooth muscle relaxation?

cGMP activates protein kinase G (PKG), which promotes MLCP activity and leads to relaxation.

how do beta adrenergic/prostacyclin receptors induce vasodilation by adenylate cyclase

adrenaline binds to receptors -> activate adenyl cyclase -> ATP turned into AMPc -> activates PKA -> phosphorylates MLCK -> MLC 20 not phosphorylated -> relaxation

what protein G is involved in beta adrenergic and prostacyclin receptors

protein Gs

what are the main metabolism pathways in a CML

1. gluc entry by GLUT1 -> glycolysis

2. NO synthesis

3. fatty acid synthesis

4. Pentose phosphate pathway -> nucleotides

What is the role of sympathetic nervous regulation in blood vessels?

Sympathetic activation typically leads to vasoconstriction or vasodilation through norepinephrine/noradrenaline NE and EPI epinephrine/adrenaline

What is the role of sympathetic nervous regulation in blood vessels on alpha-adrenergic receptors

vasoconstriction induced by NE/NA

What is the role of sympathetic nervous regulation in blood vessels on beta-adrenergic receptors

vasodilation induced by NE/NA

how does the neurotransmitters get to the CML through parasympathetic system

through the dendrites of the axon of postganglionic autonomic neuron

What is the primary effect of parasympathetic nervous regulation on blood vessels?

It induces vasodilation primarily through NO release from endothelial cells via the M3 receptor by Ach

in the parasympathetic nervous regulation what activates M3 endothelial cells

Acetylcholine -> M3 receptor -> PLC -> PIP2 -> IP3 -> RIP3 on SR -> release of Ca into cytoplasm -> Ca + CaM -> eNOS -> NO production and diffusion

the NO produced in the parasympathetic nervous regulation acts on CML

when produces in CE -> diffusion -> sGC -> cGMP -> activates PKG -> vasodilation

what are the main vasoconstrictors

adrenaline/NA/ANGII -> alpha adrenergic receptors -> PLC, IP3, RhoA/RhoK

What are the main vasodilators?

adrenaline/ANP/PG12 -> beta-adrenergic receptor -> AMPc

How do action potentials in smooth muscle cells differ from those in skeletal muscle?

They are typically slower and can involve various types of ionic channels.

what is passive relaxation of CML

inactivation/stopping of excitation-contraction mechanisms

what ATPase/pumps/exchangers are involved in passive relaxation