Membrane-permeable and -impermeable sensors of the Zinpyr family and their application to imaging of hippocampal zinc in vivo.
Esterification of fluorescent biosensors is a common strategy used to trap probes within the cell. Zinpyr-1 (ZP1) is a fluorescein-based bright fluorescent sensor for divalent zinc that is cell permeable without prior modification. We describe here the synthesis and characterization of ZP1 sensors containing a carboxylic acid or ethyl ester functionality at the 5 or 6 position of the fluorescein. The presence of an electronegative carboxylate decreases the proton-induced background fluorescence of the probe by lowering the pKa of the benzylic amines responsible for fluorescence quenching. The charged species ZP1(6-CO2-) is membrane-impermeant, whereas the permeability of the neutral ZP1(5/6-CO2Et) is similar to that of the parent sensor. Intracranial microinfusion of ZP1(6-CO2Et) into rat hippocampus produces reduced staining of vesicular zinc in neuropil and very clear delineation of zinc-positive injured neuronal somata and dendrites as compared with ZP1.
Woodroofe
Carolyn C
CC
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Masalha
Rafik
R
Barnes
Katie R
KR
Frederickson
Christopher J
CJ
Lippard
Stephen J
SJ
D000818:Animals; D015374:Biosensing Techniques / Q000379:methods*; D002462:Cell Membrane / Q000737:chemistry* / Q000502:physiology; D005452:Fluoresceins / Q000138:chemical synthesis / Q000737:chemistry*; D006367:HeLa Cells; D006624:Hippocampus / Q000737:chemistry*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015394:Molecular Structure; D009474:Neurons / Q000737:chemistry; D051381:Rats; D013050:Spectrometry, Fluorescence / Q000379:methods; D015032:Zinc / Q000032:analysis*
D005452:Fluoresceins; C501988:Zinpyr-4; D015032:Zinc; C501987:zinpyr-1