[Characterisation of 2 reversible states of the inositol 1,4,5-trisphosphate receptor in rat hepatocytes].
Myo-inositol-1,4,5-trisphosphate or (I(1,4,5)P3) is generated in liver cells after hormonal stimulation. It bind to specific receptors and induces the release of Ca2+ from an intracellular store. This receptor has been found in permeabilized hepatocytes and showed two states of low- and high-affinity with KD of 1-2 and 40-50 nmol/l, respectively. Measurements of 45Ca2+ release, mediated by different analogues, revealed that the low-affinity site was coupled to the Ca2+ channel open state. The pretreatment of cells with vasopressin, an I(1,4,5)P3-dependent agonist, induced an 60 percent increase of the binding capacity of the high-affinity sites. Incubation with 1 mumol/l Ca2+ increased the number of high-affinity sites from 5 to 65 fmol/10(6) cells. This effect was associated with a decrease in the number of low-affinity sites from 130 to 80 fmol/10(6) cells. Our results suggest that the intracellular Ca2+ concentration rise mediated by I(1,4,5)P3-dependent agonists, induced a conversion of the low-affinity form of the I(1,4,5)P3 receptor, coupled to Ca2+ release, to a desensitized high-affinity one. This process could explain the oscillations of the intracellular Ca2+ concentration observed in hormone-treated single cells.
Pietri
F
F
Unité de Recherche de Physiologie et de Pharmacologie Cellulaire, INSERM U 274, Université Paris-Sud, Orsay.
Hilly
M
M
Claret
M
M
Mauger
J P
JP
D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000187:drug effects; D005260:Female; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D014667:Vasopressins / Q000494:pharmacology
D014667:Vasopressins; D002118:Calcium
Caractérisation de deux états interconvertibles du récepteur de l'inositol 1,4,5-trisphosphate dans les hépatocytes de rat.