Dual action of arachidonic acid on calcium mobilization in avian granulosa cells.
The primary aim of this study was to evaluate the effects of arachidonic acid (AA) on calcium mobilization from intracellular compartments in digitonin-permeabilized granulosa cells isolated from the largest preovulatory follicles of laying hens. At low concentrations (ED50 0.2 microM) AA released 35% 45Ca from the endoplasmic reticulum (ER), whereas at higher concentrations (ED50 16 microM) it stimulated 45Ca efflux from mitochondria. These effects of AA were mimicked at 10-20 times lower concentration by the calcium ionophore A23187. Inositol 1,4,5-trisphosphate (IP3) also stimulated 45Ca efflux from the ER, with a markedly lower potency than AA (ED50 6.2 microM), as well as exhibiting a biphasic response. Heparin abolished the effect of IP3 and luteinizing hormone (LH), but it had no influence on AA-promoted 45Ca efflux. Moreover, the actions of IP3 and AA were additive, indicating that AA and IP3 access different Ca pools in the ER by different mechanisms. Several other unsaturated fatty acids also stimulated 45Ca mobilization from both ER and mitochondria but, with the exception of eicosapentaenoic acid, were significantly less effective than AA. It is concluded that free AA, at submicromolar concentrations that might be viewed as physiological, is a potent calcium mobilizing agent and thus may play an important role in signal transduction in avian granulosa cells, akin to that of IP3. At high (greater than 10 microM) concentrations AA removes Ca2+ from the mitochondria, an action that may be responsible for its reported inhibitory effects on steroidogenesis and other cellular functions.
Hertelendy
F
F
Department of Obstetrics and Gynecology, St. Louis University School of Medicine, MO 63104.
Molnár
M
M
Jamaluddin
M
M
D000704:Analysis of Variance; D000818:Animals; D016718:Arachidonic Acid / Q000494:pharmacology*; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002463:Cell Membrane Permeability; D002645:Chickens; D004072:Digitonin / Q000737:chemistry / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D005260:Female; D006107:Granulosa Cells / Q000187:drug effects / Q000378:metabolism*; D006493:Heparin / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000494:pharmacology; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism
D016718:Arachidonic Acid; D000001:Calcimycin; D015544:Inositol 1,4,5-Trisphosphate; D007986:Luteinizing Hormone; D006493:Heparin; D004072:Digitonin; D002118:Calcium