Myoplasmic binding of fura-2 investigated by steady-state fluorescence and absorbance measurements

Biophys J. 1988 Dec;54(6):1089-104. doi: 10.1016/S0006-3495(88)83045-5.


Binding of the fluorescent Ca2+ indicator dye fura-2 by intracellular constituents has been investigated by steady-state optical measurements. Fura-2's (a) fluorescence intensity, (b) fluorescence emission anisotropy, (c) fluorescence emission spectrum, and (d) absorbance spectra were measured in glass capillary tubes containing solutions of purified myoplasmic proteins; properties b and c were also measured in frog skeletal muscle fibers microinjected with fura-2. The results indicate that more than half, and possibly as much as 85%, of fura-2 molecules in myoplasm are in a protein-bound form, and that the binding changes many properties of the dye. For example, in vitro characterization of the Ca2+-dye reaction indicates that when fura-2 is bound to aldolase (a large and abundant myoplasmic protein), the dissociation constant of the dye for Ca2+ is three- to fourfold larger than that measured in the absence of protein. The problems raised by intracellular binding of fura-2 to cytoplasmic proteins may well apply to cells other than skeletal muscle fibers.

Publication types

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

MeSH terms

  • Action Potentials
  • Animals
  • Benzofurans*
  • Calcium / metabolism*
  • Creatine Kinase / metabolism
  • Fructose-Bisphosphate Aldolase / metabolism
  • Fura-2
  • Glyceraldehyde-3-Phosphate Dehydrogenases / metabolism
  • In Vitro Techniques
  • Kinetics
  • Models, Theoretical
  • Muscle Contraction
  • Muscle Proteins / metabolism
  • Muscles / physiology*
  • Osmolar Concentration
  • Rana temporaria
  • Spectrometry, Fluorescence / methods


  • Benzofurans
  • Muscle Proteins
  • Glyceraldehyde-3-Phosphate Dehydrogenases
  • Creatine Kinase
  • Fructose-Bisphosphate Aldolase
  • Calcium
  • Fura-2