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

• Published in: The Journal of biological chemistry Vol. 274; no. 1; pp. 175 - 182
• Main Authors: Rzigalinski, Beverly A., Willoughby, Karen A., Hoffman, Stuart W., Falck, J.R., Ellis, Earl F.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.01.1999; American Society for Biochemistry and Molecular Biology
• Subjects: 8,11,14-Eicosatrienoic Acid - analogs & derivatives; 8,11,14-Eicosatrienoic Acid - antagonists & inhibitors; 8,11,14-Eicosatrienoic Acid - metabolism; 8,11,14-Eicosatrienoic Acid - pharmacology; Animals; Arachidonic Acid - pharmacology; Astrocytes - drug effects; Astrocytes - metabolism; Calcium - metabolism; Cytochrome P-450 Enzyme Inhibitors; Enzyme Inhibitors - pharmacology; Ion Transport; Phospholipases A - antagonists & inhibitors; Phospholipases A2; Rats; Signal Transduction; Thapsigargin - antagonists & inhibitors; Thapsigargin - pharmacology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.274.1.175

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 Ca2+ from intracellular stores and capacitative Ca2+ influx. Capacitative influx of extracellular Ca2+ was inhibited by blockade of the two critical steps in epoxyeicosatrienoic acid synthesis: release of arachidonic acid from phospholipid stores by cytosolic phospholipase A2 and cytochrome P450 metabolism of arachidonic acid. AAOCF3, which inhibits cytosolic phospholipase A2, 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, orN-methylsulfonyl-6-(2-propargyloxyphenyl)hexanamide, a substrate inhibitor of P450 arachidonic acid metabolism, also blocked thapsigargin-stimulated Ca2+ influx. Nano- to picomolar 5,6-epoxyeicosatrienoic acid induced [Ca2+]ielevation consistent with capacitative Ca2+ 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.