GCaMP4

GCaMP4 is a generation of genetically encoded calcium indicators in the GCaMP family, designed to report intracellular calcium dynamics by fluorescence changes. GCaMP indicators are single fluorescent proteins engineered by fusing a circularly permuted GFP to calmodulin and an M13 peptide. When calcium binds to calmodulin, a conformational rearrangement enhances the fluorescence of GFP, providing a readout proportional to intracellular Ca2+ levels.

Compared with earlier GCaMP versions, GCaMP4 variants were developed to improve brightness, dynamic range, and the ability to detect calcium transients with more sensitivity. The design aims to produce larger fluorescence changes upon calcium binding while maintaining suitable expression levels and compatibility with common imaging modalities. Within the GCaMP4 family, variants were optimized for different kinetic properties to suit various experimental needs, such as capturing rapid neuronal activity or longer-lasting signals.

Applications of GCaMP4 include imaging neuronal activity in cultured cells and in living animals. It is widely used in neuroscience research to monitor population activity, single-cell dynamics, and calcium signaling across diverse model organisms. Expression is typically achieved through genetic delivery methods such as plasmids or viral vectors, under cell-type specific promoters to target neurons or other cell types. Imaging can be performed with one-photon or two-photon microscopy, depending on experimental requirements. Considerations for use include potential buffering of calcium by the sensor, photobleaching, and pH sensitivity, all of which can influence signal interpretation.