The existence of arterial myogenic tone was first described by Bayliss in 1902, however, its association with
pressure-dependent membrane depolarization was not observed until 1984. The factors that mediate myogenic arterial
constriction remain unknown. One possible clue was a finding by our laboratory that cerebral arterial muscle cells express
CYP 4A ω-hydroxylase enzyme that catalyzes the formation of the potent vasoconstrictor 20-hydroxyeicosatetraenoic
acid (20-HETE) from arachidonic acid (AA), the production of which increased by elevations of intravascular pressure.
20-HETE activates protein kinase C (PKC), inhibits Ca2+-activated K+ (KCa) channels, depolarizes arterial muscle cell
membrane, activates L-type Ca2+ channels, increases intracellular Ca2+ ([Ca2+]i) and mediates autoregulation of cerebral
blood flow. Emerging evidence indicates that 20-HETE level increases in ischemia/reperfusion injury and stimulates production
of reactive oxygen species (ROS) resulting in oxidative stress induced ischemic stroke injury, which can be prevented
by inhibition of 20-HETE synthesis or action. The brain also expresses CYP epoxygenases that convert AA to the
vasodilator epoxyeicosatrienoic acids (EETs), the production of which increases in ischemia and provide protection
against ischemia-induced tissue damage. Basal or stimulus released ROS act to modify cerebral myogenic tone. Similar
to other enzymes CYP epoxygenase and ω-hydroxylase also generate ROS that modify myogenic cerebral reactivity.
Hypoxia per se or adenosine released during hypoxia induces increased production of ROS that alter cerebrovascular
function. The capacity of the brain to express CYP enzymes that produce bioactive EETs and 20-HETE and generate ROS
has a significant bearing in regulating the dynamics of cerebral blood flow and serve as potential therapeutic targets for
the management of pathologic disorders of the cerebral circulation.
Keywords: Cerebral arterial muscle, membrane potential, myogenic tone, CYP enzymes, ROS, cerebral blood flow, cerebrovascular
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