Non-calcium environmental sensitivity of intracellular Indo-1.
Several mechanisms might account for the difference between spectra of Indo-1 measured on intracellular and on extracellular dye. Experiments to discriminate between various possibilities used quantitative analyses of intracellular and extracellular Indo-1 spectra. Intracellular calcium-free dye showed a 20-nm blue shift, when compared with the extracellular case. However, the calcium-bound spectrum was unaffected by the intracellular milieu. This eliminated the possibility that the spectral shift was due to calcium-independent unhydrolyzed dye. The spectral shift was reversible and was seen in resting cells as well as calcium-depleted cells. Since the apparent dissociation constant for calcium was not detectably different inside the cell, the possibility of competitive binding to another divalent cation, such as Zn2+, was eliminated as the principle source of the spectral shift. The shift appears to be due to a noncompetitive solvent effect on the emission of the calcium-free dye that is absent in the calcium-bound form.
Owen
C S
CS
Department of Biochemistry, Jefferson Medical College, Philadelphia, Pennsylvania 19107.
Sykes
N L
NL
Shuler
R L
RL
Ost
D
D
D000818:Animals; D001667:Binding, Competitive; D002118:Calcium / Q000032:analysis*; D002138:Calibration; D005260:Female; D016257:Fura-2; D007211:Indoles; D051379:Mice; D008807:Mice, Inbred BALB C; D012680:Sensitivity and Specificity; D013050:Spectrometry, Fluorescence; D013154:Spleen / Q000166:cytology / Q000378:metabolism*; D015032:Zinc / Q000378:metabolism
D007211:Indoles; D015032:Zinc; C048960:indo-1; D002118:Calcium; D016257:Fura-2