Enhanced aqueous solubility of long wavelength voltage-sensitive dyes by covalent attachment of polyethylene glycol

Abstract

Long wavelength voltage-sensitive dyes (VSDs) called Pittsburgh (PGH) dyes were recently synthesized by coupling various heterocyclic groups to a styryl-thiophene intermediate forming extended, partially rigidized chromophores. Unlike most styryl VSDs, dyes with a sulfonic acid anchor directly attached to the chromophore showed no solvatochromic absorption shifts. The limited water solubility of many long wavelength VSDs requires the use of surfactants to transport the dye through aqueous media and effectively label biological membranes. Here, we tested the chemical substitution of the sulfonic acid moiety with polyethyleneglycol (PEG) chains ranging from MW 750 to 5000, to overcome the poor solubility of VSDs while retaining their properties as VSDs. The chemical synthesis of PGH dyes and their PEG derivatives are described. The PEGderivatives were soluble in aqueous solutions (> 1 mM) and still reported membrane potential changes. In frog and mouse hearts, the voltage sensitivity (ΔF/F per action potential) and spectral properties of PEG dyes were the same as the sulfonated analogs. Thus, the solubility of VSDs can be considerably improved with small polyethyleneglycol chains and can provide an effective approach to improve staining of excitable tissues and optical recordings of membrane potential.

Cyanine Dyes Containing Quinoline Moieties: History, Synthesis, Optical Properties, and Applications

“…These salts are an essential step in the synthesis of cyanine dyes. A lot of different types of salts have been synthesized and various methods have been optimized [30–34] . There are over 180 published salts synthesized by various methods from quinaldine and almost 450 salts from lepidine [28] …”

“…Most of them are synthesized from lepidine and quinaldine directly, for example, salts 1 – 6 (Scheme 4) and 8 – 13 (Scheme 5), whereas some of them require a different initial reagent, such as diphenylamine for the synthesis of salts 7 (Scheme 4) and 14 (Scheme 5). [30, 31, 33–48] …”

Normalization of Voltage-Sensitive Dye Signal with Functional Activity Measures

“…This is especially true for complex preparations such as the in vivo cortex, where dye must be hydrophilic enough to permeate the cortical mantle, but must be hydrophobic enough to attach to the cell membrane and not be readily washed out [13] . Novel dyes which provide favorable compromises between these two opposing characteristics are under active development [6] , [23] , [24] . Since cortical staining with voltage-sensitive dye will inevitably contain a certain degree of “patchiness,” an ideal normalization method should be insensitive to the quality of staining.…”

Basic Concepts of Optical Mapping Techniques in Cardiac Electrophysiology

“…Each styryl molecule is anchored in the aqueous extracellular space by a hydrophilic negatively charged sulphonyl group, whereas the other end of the molecule is held within the bilayer lipid membrane by a lipophilic hydrocarbon chain (Efimov & Cheng, 2002). Most styryl dyes require an additional reagent (i.e., dimethyl sulphoxide [DMSO] or Pluronics) to transport them from the aqueous medium to the tissue (Patrick et al, 2007). …”