Roles of Ca2+, inositol trisphosphate and cyclic ADP-ribose in mediating intercellular Ca2+ signaling in sheep lens cells.
To further characterize how gap junction-dependent Ca2+ waves propagate between sheep lens cells, we examined the possible roles of inositol 1,4,5-trisphosphate (IP3), Ca2+ and cyclic ADP-ribose (cADPR) in mediating intercellular Ca2+ waves. Second messengers were microinjected into a single cell in a monolayer of sheep lens cells while monitoring cytosolic Ca2+ with fura-2 and fluorescence microscopy. All three compounds initiated intercellular Ca2+ waves, but more cells responded following the injection of either IP3 or cADPR than responded following the injection of Ca2+. When either IP3 or cADPR was co-injected with the Ca2+ chelator EGTA, cytosolic Ca2+ in the injected cell decreased but cytosolic Ca2+ in the adjacent cells increased, indicating that the intercellular messenger was IP3 or cADPR, rather than Ca2+. The phospholipase C inhibitor U73122 eliminated mechanically initiated intercellular Ca2+ waves, indicating that mechanical initiation probably requires IP3 production. In U73122-treated cells, injected IP3 initiated an intercellular Ca2+ wave in which the number of cells responding increased as the amount of IP3 injected increased, indicating that the distance traveled by the Ca2+ wave was dependent on cell-to-cell diffusion of IP3. In contrast, the ability of cADPR both to increase cytosolic Ca2+ in the injected cell and to initiate intercellular Ca2+ waves was greatly attenuated by U73122. In conclusion, Ca2+, IP3 and cADPR can all mediate intercellular Ca2+ waves by passing through gap junction channels, but both IP3 and cADPR are more effective intercellular messengers than Ca2+.
Churchill
G C
GC
Department of Biochemistry, University of Minnesota, St. Paul, MN 55108, USA.
Louis
C F
CF
D000818:Animals; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D002450:Cell Communication; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004963:Estrenes / Q000494:pharmacology; D017629:Gap Junctions / Q000502:physiology*; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology / Q000502:physiology*; D017136:Ion Transport; D007908:Lens, Crystalline / Q000166:cytology* / Q000378:metabolism; D008845:Microinjections; D008856:Microscopy, Fluorescence; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D011064:Poly Adenosine Diphosphate Ribose / Q000494:pharmacology / Q000502:physiology*; D011760:Pyrrolidinones / Q000494:pharmacology; D012756:Sheep; D015398:Signal Transduction / Q000502:physiology*; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000502:physiology
D002614:Chelating Agents; D004791:Enzyme Inhibitors; D004963:Estrenes; D011760:Pyrrolidinones; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D011064:Poly Adenosine Diphosphate Ribose; D004533:Egtazic Acid; D015544:Inositol 1,4,5-Trisphosphate; D010738:Type C Phospholipases; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D002118:Calcium