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

Biophys J. 1995 Dec;69(6):2378-91. doi: 10.1016/S0006-3495(95)80107-4.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Calcium / metabolism*
  • Calcium Radioisotopes
  • Cell Membrane / metabolism
  • Cell Membrane Permeability
  • Fluorescent Dyes
  • Fura-2
  • HL-60 Cells
  • Humans
  • Inositol 1,4,5-Trisphosphate / administration & dosage
  • Inositol 1,4,5-Trisphosphate / metabolism
  • Inositol 1,4,5-Trisphosphate / pharmacology*
  • Kinetics
  • Mathematics
  • Microchemistry
  • Models, Theoretical
  • Patch-Clamp Techniques
  • Perfusion / methods
  • Subcellular Fractions / metabolism
  • Time Factors


  • Calcium Radioisotopes
  • Fluorescent Dyes
  • Inositol 1,4,5-Trisphosphate
  • Calcium
  • Fura-2