Biomedical Engineering Reference
In-Depth Information
Tabl e 7. 8.
Approximated extracellular ATP levels in various tissues (Source: [
685
]).
Tissue
Bulk amount
20-100 pmol/10
6
Guinea pig heart endothelium
cells
27 pmol/10
6
Rat caudal artery endothelium
cells
Bovine aortic endothelium
2-20 nmol
Vascular endothelium
7-105 nmol
Airway epithelium
0.1-20 nmol
Human renal epithelium
350-2,000 nmol
heads with actin. Calcium binding to Ca
2
+
-binding protein relieves the inhibition.
Calponin that binds to actin and calmodulin may enhance PKC-ERK1/2 signaling.
Smooth muscle-specific Ca
V
1.2b channel is phosphorylated by PKA, PKC, and
CamK. Most of the Ca
V
channels are packed with Na
+
-Ca
2
+
exchanger NCX1,
Na
+
-K
+
pump, plasmalemmal Ca
2
+
ATPase and large-conductance Ca
2
+
-activated
K
+
channel (BK
V
,
Ca
).
β
-Adrenoceptor stimulation activates PKA that, in cooperation with AKAP,
phosphorylates Ca
V
channels. The cAMP-PKA axis can be counteracted by nitric
oxide and its effector protein kinase-G. The latter inhibits Ca
V
channels, and
activates BK
V
,
Ca
and MLCP proteins.
7.9
ATP Signaling in Blood Vessel Walls
The nucleotide adenosine 5
-triphosphate is a cell's energy source
43
and auto- and
paracrine signaling regulator that targets its cognate plasmalemmal receptors on
nearly all cell types (Vol. 3 - Chaps. 1. Signal Transduction, 2. Membrane Ion
Carriers, and 7. G-Protein-Coupled Receptors; Table
7.8
).
Extracellular ATP is involved in physiological (e.g., blood vessel tone regulation
[functional reactive hyperemia, hypoxia-induced vasodilation, and
-adrenoceptor-
mediated vasoconstriction]) and pathophysiological (e.g., atherosclerosis) pro-
cesses. Various carriers are involved in the controlled ATP release from vascular
cells (vascular endothelial and smooth muscle cells and perivascular sympathetic
neurons) as well as circulating red blood capsules, such as energy-consuming
transmembrane F
0
-F
1
ATP synthase complex, ATP-binding cassette (ABC) trans-
porters, connexin hemichannels, and pannexin channels, in addition to vesicular
exocytosis [
686
].
α
43
Mitochondrial ATP synthase produces ATP using electron carrier NADH generated in the citric
acid cycle and electron transfer through the electron transport chain, inorganic phosphate, ADP,
and oxygen. The cell uses ATP for active transport of molecules across the plasma membrane,
contraction of actin-myosin filaments, and protein phosphorylation by kinases.
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