Intracellular fluorescent probe concentrations by confocal microscopy

Biophys J. 1998 Oct;75(4):1648-58. doi: 10.1016/S0006-3495(98)77607-6.


A general method is described that takes advantage of the optical sectioning properties of a confocal microscope to enable measurement of both absolute and relative concentrations of fluorescent molecules inside cells. For compartments within cells that are substantially larger than the point spread function, the fluorescence intensity is simply proportional to the concentration of the fluorophore. For small compartments, the fluorescence intensity is diluted by contributions from regions outside the compartment. Corrections for this dilution can be estimated via calibrations that are based on the intensity distribution found in a computationally synthesized model for a cell or organelle that has been blurred by convolution with the microscope point spread function. The method is illustrated with four test cases: estimation of intracellular concentration of a fluorescent calcium indicator; estimation of the relative distribution between the neurite and soma of a neuronal cell of the InsP3 receptor on the endoplasmic reticulum; estimation of the distribution of the bradykinin receptor along the surface of a neuronal cell; and relative distribution of a potentiometric dye between the mitochondria and cytosol as a means of assaying mitochondrial membrane potential.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 3T3 Cells
  • Animals
  • Calibration
  • Endoplasmic Reticulum / ultrastructure
  • Fluorescent Dyes*
  • Fura-2 / analogs & derivatives*
  • Membrane Potentials / physiology
  • Mice
  • Microscopy, Confocal / methods*
  • Mitochondria / physiology*
  • Mitochondria / ultrastructure
  • Nerve Tissue Proteins / analysis
  • Neuroblastoma
  • Organometallic Compounds
  • Potentiometry
  • Reproducibility of Results
  • Tumor Cells, Cultured


  • Fluorescent Dyes
  • Nerve Tissue Proteins
  • Organometallic Compounds
  • tetramethyl rhodamine ethyl ester
  • fura-2-am
  • Fura-2