GTP-activated communication between distinct inositol 1,4,5-trisphosphate-sensitive and -insensitive calcium pools.
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.
Ghosh
T K
TK
Department of Biological Chemistry, University of Maryland School of Medicine, Baltimore 21201.
Mullaney
J M
JM
Tarazi
F I
FI
Gill
D L
DL
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002458:Cell Fractionation; D002460:Cell Line; D002463:Cell Membrane Permeability; D006224:Cricetinae; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000494:pharmacology*; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000494:pharmacology*; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D008861:Microsomes / Q000378:metabolism / Q000648:ultrastructure; D009130:Muscle, Smooth / Q000648:ultrastructure; D010070:Oxalates / Q000494:pharmacology; D019815:Oxalic Acid; D013403:Sugar Phosphates / Q000494:pharmacology*; D014649:Vas Deferens
D007295:Inositol Phosphates; D010070:Oxalates; D013403:Sugar Phosphates; D015544:Inositol 1,4,5-Trisphosphate; D006160:Guanosine Triphosphate; D019815:Oxalic Acid; D002118:Calcium