Kinetic studies of Ca2+ binding and Ca2+ clearance in the cytosol of adrenal chromaffin cells

Biophys J. 1997 Jul;73(1):532-45. doi: 10.1016/S0006-3495(97)78091-3.


The Ca2+ binding kinetics of fura-2, DM-nitrophen, and the endogenous Ca2+ buffer, which determine the time course of Ca2+ changes after photolysis of DM-nitrophen, were studied in bovine chromaffin cells. The in vivo Ca2+ association rate constants of fura-2, DM-nitrophen, and the endogenous Ca2+ buffer were measured to be 5.17 x 10(8) M-1 s-1, 3.5 x 10(7) M-1 s-1, and 1.07 x 10(8) M-1 s-1, respectively. The endogenous Ca2+ buffer appeared to have a low affinity for Ca2+ with a dissociation constant around 100 microM. A fast Ca2+ uptake mechanism was also found to play a dominant role in the clearance of Ca2+ after flashes at high intracellular free Ca2+ concentrations ([Ca2+]), causing a fast [Ca2+]i decay within seconds. This Ca2+ clearance was identified as mitochondrial Ca2+ uptake. Its uptake kinetics were studied by analyzing the Ca2+ decay at high [Ca2+]i after flash photolysis of DM-nitrophen. The capacity of the mitochondrial uptake corresponds to a total cytosolic Ca2+ load of approximately 1 mM.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetates
  • Adrenal Medulla / physiology*
  • Animals
  • Calcium / metabolism*
  • Cattle
  • Cells, Cultured
  • Chelating Agents
  • Chromaffin Cells / physiology*
  • Cytosol / metabolism
  • Ethylenediamines
  • Fura-2
  • Kinetics
  • Microscopy, Fluorescence
  • Mitochondria / metabolism
  • Patch-Clamp Techniques
  • Photolysis
  • Ultraviolet Rays


  • Acetates
  • Chelating Agents
  • Ethylenediamines
  • DM-nitrophen
  • Calcium
  • Fura-2