GTP-activated communication between distinct inositol 1,4,5-trisphosphate-sensitive and -insensitive calcium pools

• Published in: Nature (London) Vol. 340; no. 6230; pp. 236 - 239
• Main Authors: Ghosh, Tarun K, Mullaney, Julienne M, Tarazi, Fahmy I, Gill, Donald L
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 20-07-1989
• Subjects: Animals; Biological Transport - drug effects; calcium; Calcium - metabolism; Cell Fractionation; Cell Line; Cell Membrane Permeability; Cellular biology; Cricetinae; endoplasmic reticulum; Endoplasmic Reticulum - metabolism; Guanosine Triphosphate - pharmacology; Inositol 1,4,5-Trisphosphate; Inositol Phosphates - pharmacology; Intracellular Membranes - metabolism; Male; Microsomes - metabolism; Microsomes - ultrastructure; Muscle, Smooth - ultrastructure; Oxalates - pharmacology; Oxalic Acid; Permeability; Proteins; smooth muscle; Sugar Phosphates - pharmacology; Translocation; Vas Deferens
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/340236a0

Inositol 1,4,5-trisphosphate (InsP3) is an established mediator of intracellular Ca2+ signals but little is known of the nature and organization of Ca2+ regulatory organelles responsive to InsP3. Here we derive new information from the study of Ca2+ movements induced both by InsP3 and a specific GTP-activated Ca2+ translocation process. The latter mechanism is clearly distinct from that activated by InsP3 and may involve the translocation of Ca2+ between compartments without its release into the cytosol. This idea is supported by the fact that GTP activates Ca2+ movement into the InsP3-releasable pool. In the light of this evidence we postulated that there are two intracellular Ca2+ pools distinguishable by InsP3-sensitivity and oxalate-permeability, and that movement between them is activated by GTP. We report here direct evidence for the existence and separation of two distinct Ca2+-pumping compartments with properties coinciding with those predicted. Of these, the InsP3-sensitive Ca2+ pool is identified within a purified rough endoplasmic reticulum fraction, an observation consistent with recent InsP3 receptor-localization studies. Ca2+ translocation between pools may reflect function of a class of small GTP-binding proteins known to mediate interorganelle transfer in eukaryotic cells.