Quantitative Ratiometric Ca²⁺ Imaging to Assess Cell Viability.

Area of Science:

• Cellular biology
• Physiology
• Biophysics

Background:

• Cell viability is intrinsically linked to calcium (Ca²⁺) homeostasis.
• Ca²⁺ signaling dynamics vary significantly between cell types, from slow fluctuations in non-excitable cells to millisecond transients in excitable cells like muscle fibers.
• Muscle fibers exhibit substantial Ca²⁺ transients upon electrical stimulation, increasing levels ~100-fold.

Purpose of the Study:

• To review and explain the principles and applications of fluorescent Ca²⁺ dyes for monitoring cellular Ca²⁺ dynamics.
• To provide detailed protocols for using ratiometric Fura-2 imaging to assess resting Ca²⁺ and stimulated Ca²⁺ transients in skeletal muscle cells.
• To guide the selection of appropriate Ca²⁺ dyes based on affinity and kinetics, and to explain in situ calibration for accurate Ca²⁺ concentration determination.

Main Methods:

• Review of ratiometric and non-ratiometric Ca²⁺ dye concepts, including dye selection criteria (affinity, kinetics) and staining techniques.
• Detailed protocols for ratiometric Fura-2 imaging of isolated single skeletal muscle cells.
• Application of in situ calibration techniques to translate fluorescence intensity into absolute Ca²⁺ concentrations.

Main Results:

• Fluorescent dye intensity is influenced by mass action, binding, and unbinding kinetics, necessitating careful consideration for accurate Ca²⁺ measurements.
• Established protocols enable online monitoring of resting Ca²⁺ and Ca²⁺ transients during field stimulation in skeletal muscle cells.
• Demonstrated methods for converting fluorescence data into quantitative Ca²⁺ concentration values.

Conclusions:

• Accurate validation of Ca²⁺ kinetics and amplitude requires understanding the interplay of buffer-ligand interactions and dye kinetics.
• Ratiometric Fura-2 imaging, coupled with proper calibration, provides a robust method for quantifying Ca²⁺ signaling in muscle cells.
• This work facilitates precise assessment of Ca²⁺ homeostasis crucial for understanding cell viability and function.