A cell-based functional assay using a green fluorescent protein-based calcium indicator dCys-GCaMP

Area of Science:

• Biochemistry
• Molecular Biology
• Neuroscience

Background:

• Intracellular calcium (Ca2+) level measurement is crucial for drug discovery.
• Existing assays often involve complex dye-loading or substrate-loading steps.

Purpose of the Study:

• To introduce a novel Ca2+ indicator, dCys-GCaMP, derived from green fluorescent protein.
• To develop a rapid, simple, and sensitive cell-based functional assay for measuring intracellular Ca2+ changes.
• To demonstrate the assay's utility in drug discovery, particularly for ionotropic and G protein-coupled receptors.

Main Methods:

• Development of the dCys-GCaMP Ca2+ indicator.
• Establishment of a cell-based functional assay using HEK293 cells coexpressing NMDA receptors and dCys-GCaMP.
• Stimulation with glutamate and assessment of fluorescence changes in response to agonists, antagonists, channel blockers, and modulators.
• Comparison of results with conventional assays (Fluo-4) and literature values.
• Application to the α1A adrenergic receptor (a G protein-coupled receptor).

Main Results:

• The dCys-GCaMP assay demonstrated sensitivity and reliability in measuring cellular responses to NMDA receptor modulators.
• Fluorescence intensity increased in an agonist concentration-dependent manner and was blocked by antagonists and channel blockers.
• Pharmacological parameters obtained using dCys-GCaMP closely matched those from conventional assays and literature.
• The assay proved adaptable for G protein-coupled receptors, exemplified by studies on the α1A adrenergic receptor.
• Initial evaluation suggested suitability for high-throughput screening.

Conclusions:

• The dCys-GCaMP assay provides a sensitive, reliable, and simplified method for measuring intracellular Ca2+ dynamics.
• This novel assay eliminates the need for dye-loading or substrate-loading, streamlining drug discovery processes.
• The assay is versatile, applicable to both ionotropic and G protein-coupled receptors, and adaptable for high-throughput screening environments.