# Functional Microendoscopy Reveals Calcium Responses of Single Cells in Tracheal Tuft Cells and Kidney Podocytes

## TL;DR

A new microendoscope allows detailed imaging of single cells in hard-to-reach areas like the trachea and kidneys, capturing calcium and redox signals.

## Contribution

A cost-effective, thin multicore-fiber microendoscope enables in vivo and in situ functional imaging of single cells with high resolution.

## Key findings

- The microendoscope successfully captured calcium dynamics in murine tracheal tuft cells and kidney podocytes.
- Ratiometric redox reactions were recorded in various biological settings, including explanted organs and pancreatic islet cultures.
- The system achieved an effective resolution of 4.6 µm, resolving subcellular structures.

## Abstract

Microendoscopy, a crucial technology for minimally invasive investigations of organs, facilitates studies within confined cavities. However, conventional microendoscopy is often limited by probe size and the constraint of using a single excitation wavelength. In response to these constraints, a multichannel microendoscope with a slender profile of only 360 µm is engineered. Functional signals both in situ and in vivo are successfully captured from individual single cells, employing a specially developed software suite for image processing, and exhibiting an effective resolution of 4.6 µm, allowing for the resolution of subcellular neuronal structures. This system enabled the first examination of calcium dynamics in vivo in murine tracheal tuft cells (formerly named brush cells) and in situ in kidney podocytes. Additionally, it recorded ratiometric redox reactions in various biological settings, including intact explanted organs and pancreatic islet cultures. The flexibility and streamlined operation of the microendoscopic technique open new avenues for conducting in vivo research, allowing for studies of tissue and organ function at cellular resolution.

A cost‐effective multicore‐fiber microendoscope for biological functional imaging is presented. The instrument is thin enough to image within the mouse trachea. It is applied to record responses of tracheal tuft cells to stimulation in vivo, as well as calcium and redox signals from various organs in situ. Additionally, the system's optical characterization, data processing pipeline, and multichannel capabilities are demonstrated.