12 - Vascular Endothelial Cell Physiology Flashcards
The endothelium fulfills a variety of different functions involved in __________, the _______, and the __________
The endothelium fulfills a variety of different functions involved in maintenance of the vascular wall, the circulating blood, and the hemodynamic balance of the entire body
Which layer of the vasculature contains endothelium?
Tunica intima
six functions of endothelial cells
- Physical lining
- Permeability barrier for exchange of nutrients
- Mediates angiogenesis
- Regulates platelet function
- Influences smooth muscle proliferation in disease such as atherosclerosis
- Secrete paracrine agents to modify smooth muscle function (vasodilators and constrictors)
What are the three primary vasodilators produced by the endothelium?
- Nitric oxide
- Prostaglandins such as prostacyclin (PG12)
- Endothelium-derived hyperpolarizing factors (EDHF’s)
Three roles of NO in the cardiovascular system?
- Platelet aggregation (inhibitor)
- Cell proliferation (inhibitor)
- Vascular smooth muscle tone
What is the half life of nitric oxide (NO)?
5 seconds
NO is _______ and thus can cross membranes
NO is lipophilic and thus can cross membranes
What are the three forms of NO synthase (NOS)?
- Neuronal NOS (nNOS; Type I)
- Inducible NOS (iNOS; Type II)
- Endothelial NOS (eNOS; Type III)
Which NO synthases (NOSs) are Ca++ dependent?
eNOS and nNOS (Neuronal NOS and endothelial NOS)
Which NO synthase (NOS) is Ca++ Independent?
i-NOS (inducible NOS)
How is eNOS activated?
- activated by ACh, bradykinin / shear stress opening Ca++ channel
- Ca++ influx → CaM → eNOS
- L-argenine is converted to NO by eNOS (using BH4, FAD, FMN, NADPH) and side product L-citrulline
Explain the image of shear stress and receptor-stimulated NO formation:
- Endothelial (e)-NOS isoform converts ________ to NO. eNOS activity is determined by ________ and/or _______ state at different sites
- eNOS activity is positively modulated by ___________
- eNOS activity is negatively modulated by _______________
- eNOS activity is inhibited by its interaction with _______ and by ________ modification
- eNOS association with _________ favors activation
- Endothelial (e)-NOS isoform converts L-arginine to NO. eNOS activity is determined by intracellular calcium concentration and/or phosphorylation state at different sites
- eNOS activity is positively modulated by phosphorylation of serine 1177 (S1177)
- eNOS activity is negatively modulated by phosphorylation of threonine 494 (T494)
- eNOS activity is inhibited by its interaction with caveolin-1 and by O-GlcNAc modification
- eNOS association with heat shock protein 90 (hsp90) favors activation
*
- eNOS association with heat shock protein 90 (hsp90) favors activation
Explain the image:
Aging impacts of NO
- In endothelial aging, NO synthesis is compromised because ___________\_, reduced expression and association iwth ____________, ____________ and ___________\_
- Reduced availability of ___________\_and ___________\_ induces ____________ generation
- In aged endothelial cells, up-regulated ___________\_which may be associated with ____________, produces high levels of ___________\_
- NO reacts with ___________\_residues of proteins (arginase for example), forming S-nitrosothiol (-SNO)-arginase generating the harmful reactive nitrogen species ____________, which contributes to ___________\_
- The aging-associated NOS alterations are depicted in red
- In endothelial aging, NO synthesis is compromised because eNOS activity is decreased due to increased expression and interaction with caveolin, reduced expression and association iwth hsp90, reduced phosphorylation of S<u>1177</u> and increased phosphorylation of T<u>494</u>
- Reduced availability of L-arginine and tetrahydrobiopterin (BH<u>4</u>) induces eNOS uncoupling or changes the enzyme to a state that favours superoxide anion generation
- In aged endothelial cells, up-regulated iNOS which may be associated with NF-kB-induced vascular inflammation, produces high levels of NO
- NO reacts with cysteine residues of proteins (arginase for example), forming S-nitrosothiol (-SNO)-arginase generating the harmful reactive nitrogen species peroxynitrite (ONOO-), which contributes to vascular dysfunction
- The aging-associated NOS alterations are depicted in red
Describe Endothelial-Dependent Relaxation
What activates NOS and what is the effect:
- NOS is activated by Ach/Metacholine/shear stress
- NOS converts L-arginine to NO and L-citrulline in the Endothelial cell
- NO diffuses out of the EC and into the VSMC where it activates guanylate cyclase to convert GTP to cGMP → ↓Ca++ → Relaxation (dilation)
Describe Endothelium independent Vasodilation
- Sodium nitroprusside/ nitroglycerin → NO→Gunylate Cyclase catalyses GTP→cGMP→↓Ca→Relaxation
How are prostaglandins (eicosanoids) produced?
Arachidonic acid (AA) – cyclooxygenase -→ PGG2 – endoperoxidase→ PGH2
PGH2 – TxA2 synthase→ Thromboxane
PGH2 – PGI2 synthase → Prostacyclin
What is the mechanism of Endothelial-derived hyperpolarization
- ↑endothelial [Ca++] → activation of endothelial ___ and ____ channels → influx of low levels of ions from the cell and _____ of the ______ membrane
- Efflux of K+ ions can have an additional effect by activating an ________ and ________ channels on the smooth muscle cells causing hyperpolarization of the smooth muscle
- Hyperpolarization of the endothelial cell membrane may then be transferred to the smooth muscle cells via __________
- ↑endothelial [Ca++] → activation of endothelial SKCa and IKCa channels → influx of low levels of K+ ions from the cell and hyperpolarization of the endothelial membrane
- Efflux of K+ ions can have an additional effect by activating an inward rectifying K+ channel (KIR) and Na+/K+ ATPase channels on the smooth muscle cells causing hyperpolarization of the smooth muscle
- Hyperpolarization of the endothelial cell membrane may then be transferred to the smooth muscle cells via myoendothelial gap junctions (MEGJ)
How is peroxynitrite produced?
Binding of NO to superoxide (O2-) leads to the formation of peroxynitrite (ONOO-)
