Two Ca2+ transport systems are distinguished on the basis of their Mg2+ dependency in a post-nuclear particulate fraction of bovine adrenal cortex.
Inositol 1,4,5-trisphosphate (InsP3) is a second messenger responsible for Ca2+ release from an internal store whose nature and location remains undefined. To get more information on this intracellular Ca2+ store, a post-nuclear particulate fraction was prepared from bovine adrenal cortex and its Ca2+ uptake and release activities were monitored with the fluorescent indicator Fura-2. In the presence of Mg2+ (2 mM), the particulate preparation showed high ATP-dependent Ca2+ sequestering activity and decreased the ambient Ca2+ concentration to about 150 nM. In the absence of Mg2+, Ca2+ was still sequestered but less efficiently, reaching a level around 170 nM. In the presence of Mg2+, the Ca2+ released by a maximal dose of InsP3 (2 microM) was completely resequestered whereas in the absence of Mg2+, no resequestration occurred even after complete degradation of InsP3. The use of selective agents such as oligomycin, saponin, ionomycin and biliary salts indicated that Ca2+ was stored in three different pools which are distinct from the mitochondria and from inside-out membrane vesicles. Our data also indicate that InsP3 releases Ca2+ from a pool which is filled up by a Mg2(+) -dependent Ca2+ ATPase.
Guillemette
G
G
Department of Pharmacology, Faculty of Medicine, University of Sherbrooke, Quebec, Canada.
Poitras
M
M
Boulay
G
G
D000255:Adenosine Triphosphate / Q000378:metabolism; D000302:Adrenal Cortex / Q000378:metabolism*; D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002417:Cattle; D016257:Fura-2; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism; D015759:Ionomycin / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology; D012503:Saponins / Q000494:pharmacology; D013658:Taurolithocholic Acid / Q000494:pharmacology
D012503:Saponins; D013658:Taurolithocholic Acid; D015759:Ionomycin; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D002118:Calcium; D016257:Fura-2