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Highly cooperative Ca2+ elevations in response to Ins(1,4,5)P3 microperfusion through a patch-clamp pipette

Jacquet, J.
Mayr, G.
Published in Biophysical Journal. 1995, vol. 69, no. 6, p. 2378-2391
Abstract To study the initial kinetics of Ins(1,4,5)P3-induced [Ca2+]i elevations with a high time resolution and to avoid the problem of cell-to-cell heterogeneity, we have used the combined patch-clamp/microfluorimetry technique. The mathematical description of the microperfusion of Ins(1,4,5)P3 and the subsequent Ca2+ release consists of a monoexponential decay (cytosolic Ins(1,4,5)P3 concentration) and a Hill equation (Ins(1,4,5)P3 dose-response curve). Two additional Hill equations and an integration were necessary to include a putative dependence of Ins(1,4,5)P3-induced Ca2+ release on [Ca2+]i. Best-fitting analysis assuming [Ca2+]i-independent Ca2+ release yielded Hill coefficients between 4 and 12. The high cooperativity was also observed with the poorly metabolizable analog Ins(2,4,5)P3 and was independent of extracellular [Ca2+]. Best-fitting analysis including a positive [Ca2+]i feedback suggested a cooperativity on the level of Ins(1,4,5)P3-induced channel opening (n = 2) and an enhancement of Ins(1,4,5)P3-induced Ca2+ release by [Ca2+]i. In summary, the onset kinetics of Ins(1,4,5)P3-induced [Ca2+]i elevations in single HL-60 granulocytes showed a very high cooperativity, presumably because of a cooperativity on the level of channel opening and a positive Ca2+ feedback, but not because of Ca2+ influx or Ins(1,4,5)P3 metabolism. This high cooperativity, acting in concert with negative feedback mechanisms, might play an important role in the fine-tuning of the cellular Ca2+ signal.
Keywords Calcium/ metabolismCalcium RadioisotopesCell Membrane/metabolismCell Membrane PermeabilityFluorescent DyesFura-2HL-60 CellsHumansInositol 1,4,5-Trisphosphate/administration & dosage/metabolism/ pharmacologyKineticsMathematicsMicrochemistryModels, TheoreticalPatch-Clamp TechniquesPerfusion/methodsSubcellular Fractions/metabolismTime Factors
PMID: 8599644
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Research group Obésité et syndrome métabolique (803)
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SCHRENZEL, Jacques et al. Highly cooperative Ca2+ elevations in response to Ins(1,4,5)P3 microperfusion through a patch-clamp pipette. In: Biophysical Journal, 1995, vol. 69, n° 6, p. 2378-2391. https://archive-ouverte.unige.ch/unige:7577

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