Inositol 1,3,4,5-tetrakisphosphate-induced Ca2+ sequestration into bovine adrenal-medullary secretory vesicles.
Ins(1,3,4,5)P4 induced a rapid sequestration of Ca2+ into both secretory vesicles and microsomes of bovine adrenal medulla. The Ca(2+)-sequestering role of Ins(1,3,4,5)P4 contrasts with the Ca(2+)-releasing role of Ins(1,4,5)P3 in adrenal-medullary secretory vesicles and microsomes. The Ins(1,3,4,5)P4-induced Ca2+ sequestration into secretory vesicles was not inhibited by heparin (50 micrograms/ml), whereas Ins(1,4,5)P3-induced Ca2+ release was completely inhibited, indicating two different receptors for Ins(1,4,5)P3 and Ins(1,3,4,5)P4. Furthermore, Ins(1,3,4,5)P4 was as effective at 4 degrees C as at 24 degrees C in sequestering Ca2+ into secretory vesicles, implying Ca2+ sequestration through receptor-operated Ca2+ channels or activation of the Ca(2+)-exchange mechanism by Ins(1,3,4,5)P4. The Ca(2+)-sequestering activity of Ins(1,3,4,5)P4 has also been demonstrated with 45Ca2+; 10 microM-Ins(1,3,4,5)P4 induced rapid uptake of 45Ca2+ into secretory vesicles optimized for Ca2+ uptake, whereas 10 microM-Ins(1,4,5)P3 induced 45Ca2+ release from secretory vesicles in similar experiments.
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Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas 75235.
D000313:Adrenal Medulla / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D002837:Chromaffin Granules / Q000378:metabolism; D006493:Heparin / Q000378:metabolism; D007295:Inositol Phosphates / Q000378:metabolism*; D008861:Microsomes / Q000378:metabolism
D007295:Inositol Phosphates; C081655:inositol-1,3,4,5-tetrakisphosphate; D006493:Heparin; D002118:Calcium