Ca²⁺ Staining Technique

Using the Ca²⁺ fluorescent probe Fluo-4 AM (HY-101896) as an example, this section outlines the experimental methods and procedures for Ca²⁺ staining.

Fluo-4 AM is a synthetic Ca²⁺ fluorescent probe based on a fluorescein structure; its staining mechanism relies on the selective chelation of Ca²⁺ by the dicarboxylate groups within its molecular structure. Upon binding with Ca²⁺, intramolecular charge transfer triggers a redistribution of electron cloud density within the conjugated system, resulting in an 80- to 100-fold enhancement in fluorescence intensity. This enables highly sensitive detection of intracellular calcium ion concentrations^[1][2].
Fluo-4 AM is an acetoxymethyl ester derivative of Fluo-4; it possesses excellent cell membrane permeability, allowing it to readily enter cells. Once inside the cell, it is hydrolyzed by intracellular esterases into Fluo-4, which subsequently binds with calcium ions and emits fluorescence. Fluo-4 AM is compatible with the optical configurations of most flow cytometers and confocal microscopes. The affinity of Fluo-4 AM for calcium ions is similar to that of Fluo-3 AM (HY-D0716), with a dissociation constant (Kd) of 345 nM^[3].

Cell Culture:

Perform routine cell culture.

Related Protocols:

• Somatic Cell Culture Protocol
• Cell Recovery Protocol

Fluo-4 AM is a commonly used probe for detecting intracellular Ca²⁺ (calcium ion) concentrations (Ex/Em = 485/526 nm).

Preparation of Stock Solution:

Prepare a 1 mM Fluo-4 AM stock solution using DMSO. Note: Fluo-4 AM is unstable in solution; it is recommended to prepare the working solution immediately before use.

Cell Staining:

Dilute the Fluo-4 AM stock solution to 1 μM using cell culture medium. Treat the cells with this working solution for 30 minutes. Note: The concentration and incubation time may be adjusted in a gradient or optimized based on preliminary experimental results.

Cell Washing:

Wash the cells three times with 1× PBS (2 minutes per wash at 3000 g) to remove any residual dye working solution.

Digestion and Collection:

Digest and collect the cells, centrifuge, and then resuspend them in 1× PBS.

Sample Preparation:

Place the cell suspension into a flow cytometry tube.

Instrument Analysis:

Perform analysis using a flow cytometer, and analyze the data using software such as CellQuest.

Detection Channel:

Green channel

Excitation Wavelength:

485 nm

Emission Wavelength:

526 nm