# An Enhanced Red Bioluminescent Indicator for Responsive Detection of Physiological Calcium Dynamics in Cells and Mice

## TL;DR

Researchers developed a new red bioluminescent sensor, eBRIC, that improves the detection of calcium activity in cells and live mice.

## Contribution

eBRIC is a novel, enhanced red bioluminescent calcium indicator with improved responsiveness and in vivo imaging capabilities.

## Key findings

- eBRIC shows significantly better Ca2+ responsiveness in assays, cultured cells, and primary neurons.
- eBRIC enables minimally invasive, video-rate in vivo imaging of Ca2+ dynamics in awake mice.
- eBRIC produced approximately double the response compared to the previous BRIC indicator in a BLA activation paradigm.

## Abstract

Calcium (Ca2+) is a crucial metal ion and signaling messenger. While bioluminescent indicators for Ca2+ have emerged as powerful imaging tools, their performance has been suboptimal. In this study, we developed an enhanced bioluminescent red indicator for Ca2+ (eBRIC) by using a physiological Ca2+ concentration range during library screening. Compared with its predecessors, this new sensor demonstrates substantially improved Ca2+ responsiveness in protein-based assays, cultured cell lines, and primary neurons. We further demonstrated the utility of eBRIC for in vivo recording of Ca2+ dynamics in the brains of live mice, using both a microscope setup and a luminescent imaging dark box. Notably, by combining eBRIC with our recently developed water-soluble luciferin, we achieved minimally invasive, video-rate imaging of Ca2+ activity in a defined brain region of awake mice. In a footshock-induced basolateral amygdala (BLA) activation paradigm, eBRIC elicited approximately double the response compared to the previous BRIC indicator. The improved responsiveness offered by eBRIC underscores its potential as a powerful tool for investigating Ca2+ dynamics in living systems.