INTRACELLULAR MEASUREMENTS IN WHOLE TISSUES

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Mechanism of EDHF Dilations in the Rat Middle
Cerebral Artery
J. You, E.M. Golding, S.P. Marrelli, and R.M.
Bryan, Jr. Departments of Anesthesiology,
Molecular Physiology and Biophysics, and
Medicine (Cardiovascular Sciences) Baylor
College of Medicine Houston, Texas
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• EDHF
• Involves Endothelium
• Not NO
• Not PGI2
• Hyperpolarizes VSM
• Involves KCa Channels
• (You et al., Stroke 30 1125, 1999)

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NDGA
MS
Figure from Roman, R. Physiological Reviews
82131, 2002
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Hypotheses Arachidonic acid that is metabolized
through the P450 epoxygenase pathway is involved
with EDHF dilations in rat cerebral
arteries. Arachidonic acid that is metabolized
through the lipoxygenase pathway is involved with
EDHF dilations in rat cerebral arteries.
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EDHF does not appear to be metabolite of P450
epoxygenase that is made on demand.
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• Activation of PLA2 is a critical step in the EDHF
  response.

PLA2

EET
Lysophospholipid
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Repeated Dilations to UTP In the presence of
L-NAME/indo
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ABT (1-aminobenzotriazole) 50 mg/kg every 12
hours for 5 days
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Mechanism of EDHF Dilations in the Rat Middle
Cerebral Artery

• Although PLA2 is involved with EDHF dilations in
  rat cerebral arteries, metabolites of the
  arachidonic acid pathways do not appear to be
  involved. These pathways includes the P450
  epoxygenase, lipoxygenase, and ?-hydroxylase.

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Mechanism of EDHF Dilations in the Rat Middle
Cerebral Artery
HypothesisArachidonic acid (without further
metabolism) can dilate cerebral arteries.
(Abstract 51) A novel mechanism of
vasodilatation in cerebral arteries Activation
of tandem pore domain potassium channels
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cPLA2 is located in both endothelium and vascular
smooth muscle in rat middle cerebral arteries.
Non-immune IgG Control
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NDGA
MS
Figure from Roman, R. Physiological Reviews
82131, 2002
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• Activation of PLA2 is a critical step in the EDHF
  response.
• (You et al. J Cerebral Blood Flow Metab 22
  1239-1247, 2002)

PLA2

Arachidonic acid
Phospholipid
Lysophospholipid
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NDGA
MS
Figure from Roman, R. Physiological Reviews
82131, 2002
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Products of PLA2 catalyzed reaction
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• EDHF
• Endothelium-derived
• Not NO
• Not PGI2
• Hyperpolarizes VSM
• Involves KCa Channels
• (You et al., Stroke 30 1125, 1999)

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• EDHF
• Endothelium-derived
• Not NO
• Not PGI2
• Hyperpolarizes VSM
• Involves KCa Channels
• (You et al., Stroke 30 1125, 1999)

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HELSS haloenol lactone suicide
substrate Ca-independent PLA2 inhibitor
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PLC appears to be involved with the EDHF response.
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AACOCF3 Inhibitor of cytoplasmic PLA2 and
Ca-independent PLA2
lu luminal application
ab abluminal application
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Candidates for EDHF

• Arachidonic Acid Metabolites
• Epoxygenase Products
• Lipoxygenase Products
• K
• Gap Junctions
• H2O2
• Anandamide

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MCA branch
Male Long Evans rats Middle cerebral arteries
(MCAs) Branches of MCAs (bMCAs) Penetrating
arterioles (PAs)
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Major Candidates for EHDF
VSM
K
Epoxygenase Products Lipoxygenase Products
Gap Junctions
Endothelium
PLA2
Possible
Acetylcholine Bradykinin ATP
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An increase in endothelial Ca2 and
hyperpolarization of the endothelium are critical
steps in the EDHF response.
Marrelli, AJP 281 H1759, 2001
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Activation of PLA2 is a critical step in the EDHF
response.
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EHDF Mechanism in Cerebral Vessels
Endothelium or VSM
P450 epoxygenase
lipoxygenase
?-hydroxylase
epoxyeicosatrienoic acids (EETs) 19- and
20-hydroxyeicosatetraenoic acids (19- and
20-HETE) and 7-, 10-, 12-, 13-, 15-, 16-,
17-, and 18-HETEs from AA
cyclooxgenase