Arachidonic acid inhibits thyrotropin-releasing hormone-induced elevation of cytoplasmic free calcium in GH3 pituitary cells.
We have shown that arachidonic acid stimulates 45Ca2+ efflux from prelabeled rat pituitary mammotropic (GH3) cells resuspended in "Ca2+-free" medium (Kolesnick, R. N., Mussachio, I., Thaw, C., and Gershengorn, M. C. (1984) Am. J. Physiol. 246, E458-E462). In this study, we further characterize the effects of arachidonic acid on Ca2+ homeostasis in GH3 cells and demonstrate its antagonism of changes induced by thyrotropin-releasing hormone (TRH). At below 5 microM, arachidonic acid stimulated intracellular for extracellular Ca2+ exchange without affecting cell Ca2+ content. Above 5 microM, arachidonic acid decreased membrane-bound Ca2+, as monitored by chlortetracycline, and decreased total cell 45Ca2+ content by depleting nonmitochondrial and mitochondrial pools. However, arachidonic acid did not elevate cytoplasmic free Ca2+ concentration ([Ca2+]i). Arachidonic acid inhibited TRH-induced 45Ca2+ efflux, loss of membrane-bound Ca2+, mobilization of nonmitochondrial Ca2+, and elevation of [Ca2+]i. Arachidonic acid also lowered elevated [Ca2+]i caused by release of mitochondrial Ca2+ with an uncoupler or by influx of extracellular Ca2+ stimulated with K+ depolarization. Hence, arachidonic acid stimulates Ca2+ extrusion from and depletes Ca2+ stores within GH3 cells. We suggest that arachidonic acid may be an important regulator of cellular Ca2+ homeostasis which may inhibit TRH-induced elevation of [Ca2+]i.
D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D002751:Chlortetracycline; D003470:Culture Media; D008564:Membrane Potentials; D008928:Mitochondria / Q000378:metabolism; D010911:Pituitary Neoplasms / Q000378:metabolism*; D051381:Rats; D012710:Serum Albumin, Bovine / Q000494:pharmacology; D013050:Spectrometry, Fluorescence; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*
D001095:Arachidonic Acids; D003470:Culture Media; D012710:Serum Albumin, Bovine; D016718:Arachidonic Acid; D013973:Thyrotropin-Releasing Hormone; D002118:Calcium; D002751:Chlortetracycline