Calcium Influx Factor, Further Evidence It Is 5,6-Epoxyeicosatrienoic Acid

Abstract

We present evidence in astrocytes that 5,6-epoxyeicosatrienoic acid, a cytochrome P450 epoxygenase metabolite of arachidonic acid, may be a component of calcium influx factor, the elusive link between release of Ca 2؉ from intracellular stores and capacitative Ca 2؉ influx. Capacitative influx of extracellular Ca 2؉ was inhibited by blockade of the two critical steps in epoxyeicosatrienoic acid synthesis: release of arachidonic acid from phospholipid stores by cytosolic phospholipase A 2 and cytochrome P450 metabolism of arachidonic acid. AAOCF 3 , which inhibits cytosolic phospholipase A 2 , blocked thapsigargin-stimulated release of arachidonic acid as well as thapsigargin-stimulated elevation of intracellular free calcium. Inhibition of P450 arachidonic acid metabolism with SKF525A, econazole, or N-methylsulfonyl-6-(2-propargyloxyphenyl)hexanamide, a substrate inhibitor of P450 arachidonic acid metabolism, also blocked thapsigargin-stimulated Ca 2؉ influx. Nanoto picomolar 5,6-epoxyeicosatrienoic acid induced [Ca 2؉ ] i elevation consistent with capacitative Ca 2؉ influx. We have previously shown that 5,6-epoxyeicosatrienoic acid is synthesized and released by astrocytes. When 5,6-epoxyeicosatrienoic acid was applied to the rat brain surface, it induced vasodilation, suggesting that calcium influx factor may also serve a paracrine function. In summary, our results suggest that 5,6-epoxyeicosatrienoic acid may be a component of calcium influx factor and may participate in regulation of cerebral vascular tone.

Metabotropic Glutamate Receptor Activation Enhances the Activities of Two Types of Ca2+-Activated K+Channels in Rat Hippocampal Astrocytes

“…This observation is consistent with our previous findings that demonstrated the ability of glutamate to stimulate release of EETs from astrocytes (Alkayed et al, 1997). In vivo, EETs may act to increase K Ca channel activity directly or may act indirectly as a calcium influx factor (Rziglinski et al, 1999) to replenish Ca 2ϩ stores necessary to sustain an increased Ca 2ϩ level for K Ca channel activation. The results of the present study in astrocytes together with the previous work on isolated vascular smooth muscle cells (Gebremedhin et al, 1992) implicate the ability of EETs to act on K Ca channels.…”

Male Mice That Do Not Express Group VIA Phospholipase A2 Produce Spermatozoa with Impaired Motility and Have Greatly Reduced Fertility

“…Arachidonic acid (20:4) facilitates Ca 2ϩ entry from the extracellular space and Ca 2ϩ release from ER (42), and 20:4-containing plasmenylethanolamine species are abundant in ER and are excellent iPLA 2 ␤ substrates (43). Moreover, Ca 2ϩ influx factor is an arachidonate oxygenation product (44), and its production could involve iPLA 2 ␤ action.…”

TRPV4 channels stimulate Ca 2 + -induced Ca 2+ release in astrocytic endfeet and amplify neurovascular coupling responses

“…Also in cultured cortical astrocytes, TRPV4 channels form complexes with aquaporin 4 to regulate cell volume responses to hypoosmotic stress (12). Notably, it has been shown that TRPV4 channels in other preparations are activated by epoxyeicosatrienoic acids (EETs) (13-15), which have been implicated in NVC (16-18) and reportedly stimulate Ca 2+ influx in rat cortical astrocytes (19,20). TRPV4 channels are thermosensitive, osmosensitive, and mechanosensitive, and thereby mediate processes by which cells sense and respond to environmental cues (21)(22)(23)(24) (25)(26)(27)(28)(29).…”