Investigation of the roles of Ca(2+) and InsP(3) diffusion in the coordination of Ca(2+) signals between connected hepatocytes.
Glycogenolytic agonists induce coordinated Ca(2+) oscillations in multicellular rat hepatocyte systems as well as in the intact liver. The coordination of intercellular Ca(2+) signals requires functional gap-junction coupling. The mechanisms ensuring this coordination are not precisely known. We investigated possible roles of Ca(2+) or inositol 1,4,5-trisphosphate (InsP(3)) as a coordinating messengers for Ca(2+) spiking among connected hepatocytes. Application of ionomycin or of supra-maximal concentrations of agonists show that Ca(2+) does not significantly diffuse between connected hepatocytes, although gap junctions ensure the passage of small signaling molecules, as demonstrated by FRAP experiments. By contrast, coordination of Ca(2+) spiking among connected hepatocytes can be favored by a rise in the level of InsP(3), via the increase of agonist concentrations, or by a shift in the affinity of InsP(3) receptor for InsP(3). In the same line, coordination cannot be achieved if the InsP(3) is rapidly metabolized by InsP(3)-phosphatase in one cell of the multiplet. These results demonstrate that even if small amounts of Ca(2+) diffuse across gap junctions, they most probably do not play a significant role in inducing a coordinated Ca(2+) signal among connected hepatocytes. By contrast, coordination of Ca(2+) oscillations is fully dependent on the diffusion of InsP(3) between neighboring cells.
Clair
C
C
INSERM U442, Université de Paris-Sud, bât 443, 91405 Orsay, France.
Chalumeau
C
C
Tordjmann
T
T
Poggioli
J
J
Erneux
C
C
Dupont
G
G
Combettes
L
L
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects; D002463:Cell Membrane Permeability / Q000187:drug effects; D004058:Diffusion / Q000187:drug effects; D004553:Electric Conductivity; D005453:Fluorescence; D016257:Fura-2 / Q000378:metabolism; D017629:Gap Junctions / Q000187:drug effects / Q000378:metabolism; D022781:Hepatocytes / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D000072181:Inositol Polyphosphate 5-Phosphatases; D015759:Ionomycin / Q000494:pharmacology; D008099:Liver / Q000166:cytology; D018613:Microscopy, Confocal; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D015759:Ionomycin; D015544:Inositol 1,4,5-Trisphosphate; D010744:Phosphoric Monoester Hydrolases; D000072181:Inositol Polyphosphate 5-Phosphatases; D002118:Calcium; D016257:Fura-2