title: GTP- and inositol 1,4,5-trisphosphate-activated intracellular calcium movements in neuronal and smooth muscle cell lines.
abstract: Recent evidence has revealed that a highly sensitive and specific guanine nucleotide regulatory process controls intracellular Ca2+ release within N1E-115 neuroblastoma cells (Gill, D. L., Ueda, T., Chueh, S. H., and Noel, M. W. (1986) Nature 320, 461-464). The present report documents GTP-induced Ca2+ release within quite distinct cell types, including the DDT1MF-2 smooth muscle cell line. GTP-induced Ca2+ release has similar GTP sensitivity and specificity among cells and rapidly mobilizes up to 70% of Ca2+ specifically accumulated within a nonmitochondrial Ca2+-pumping organelle within permeabilized DDT2MF-2 cells. Maximal GTP-induced release of Ca2+ is observed to be greater than inositol 1,4,5-trisphosphate (IP3)-induced Ca2+ release (the latter being approximately 30% of total releasable Ca2+). After maximal IP3-induced release, further IP3 addition is ineffective, whereas subsequent addition of GTP further releases Ca2+ to equal exactly the extent of Ca2+ release observed by addition of GTP in the absence of IP3. This suggests that IP3 releases Ca2+ from the same pool as GTP, whereas GTP also releases from an additional pool. The effects of GTP appear to be reversible since simple washing of GTP-treated cells restores their previous Ca2+ uptake properties. Electron microscopic analysis of GTP-treated membrane vesicles reveals their morphology to be unchanged, whereas treatment of vesicles with 3% polyethylene glycol, known to enhance GTP-mediated Ca2+ release, clearly induces close coalescence of membranes. In the presence of 4 mM oxalate, GTP induces a rapid and profound uptake, as opposed to release, of Ca2+. The findings suggest that GTP-activated Ca2+ movement is a widespread phenomenon among cells, which can function on the same Ca2+ pool mobilized by IP3, and although activating Ca2+ movement by a mechanism distinct from IP3, does so via a process that does not appear to involve fusion between membranes.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D002463:Cell Membrane Permeability; D006160:Guanosine Triphosphate / Q000494:pharmacology*; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000494:pharmacology*; D007425:Intracellular Membranes / Q000378:metabolism / Q000648:ultrastructure; D007700:Kinetics; D008854:Microscopy, Electron; D008861:Microsomes / Q000378:metabolism / Q000648:ultrastructure; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D009447:Neuroblastoma; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism; D013403:Sugar Phosphates / Q000494:pharmacology*
chemical_list: D007295:Inositol Phosphates; D013403:Sugar Phosphates; D015544:Inositol 1,4,5-Trisphosphate; D006160:Guanosine Triphosphate; D002118:Calcium