Biomedical Engineering Reference
In-Depth Information
Table 9.12.
Potassium channels of endothelial cells (Source: [
895
]). K
+
channels induce hyper-
polarization, in particular Ca
2
+
-sensitive K
+
channels after Ca
2
+
entry in endothelial cells.
Ion carriers
Features
Inwardly rectifying
Expression in the macrocirculation;
K
+
channels
Location on wetted side of endocardium;
K
+
sensor
(potential threshold based on
extracellular K
+
level)
Downregulation by reduction in
intracellular ATP and hypoxia
Inhibition by phosphatase PP2a, angiotensin-2,
vasopressin, vasoactive intestinal polypeptide,
endothelin-1, and histamine
Hemodynamic stress gating
(K
IR
2.1)
Ca
2
+
-dependent
EC type-dependent expression;
K
+
channels
Ca
2
+
- and voltage-gating;
Fluid flow sensitivity (SK and BK)
BK
Activation by ryanodine receptor
Activation by IP
3
-induced Ca
2
+
release
(ATP, acetylcholine, bradykinin)
IK
SK
Voltage-independent, calmodulin-dependent
ATP-sensitive
Activation by low ATP cellular level;
K
+
channels
Shear stress-mediated vasodilation (?)
Carriers for K
+
and Na
+
Stretch-activated
K
+
-permeable
channels
Voltage-activated Na
+
channels are stimulated by PKC kinase. Epithelial Na
+
channels may be connected to water transport via aquaporin-4.
Calcium-dependent Cl
−
channels, outward rectifiers, require ATP agent.
Endothelial cell expresses other Cl
−
channels, including high-conductance Cl
−
channels, which are quasi-silent in intact cells, and cAMP-stimulated CFTRs.
9.5.5
Hormones and Vasoactive Substances
Functions of the endothelium are affected by hemodynamics. The intracellular
calcium concentration in cultured endothelial cells strongly depends on flow
pattern.
48
Although oscillatory flow does not change [Ca
2
+
]
i
, steady and pulsatile
48
Cultured bovine aortic endothelial cells have been subjected to steady shear stress (0.02-7 N/m
2
),
non-zero mean sinusoidal shear stress, either with a strong mean component (4
+
/−
2N/m
2
)or
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