# Ca2+ influx through muscle-type nicotinic acetylcholine receptors in zebrafish contributes to contractions and development of slow muscle cells in early development

## TL;DR

Zebrafish slow muscle cells rely on calcium influx through specific receptors for proper development and movement.

## Contribution

The study reveals a novel role of Ca2+ influx through AChRs in zebrafish slow muscle development and function.

## Key findings

- Transgenic zebrafish with Ca2+-impermeable AChRs showed reduced locomotor activity.
- Slow muscle cells in transgenic zebrafish lacked sustained Ca2+ responses and developed thinner muscles.
- Calcium influx through AChRs is crucial for muscle contraction and development in zebrafish larvae.

## Abstract

Although the difference between the characteristics of fast and slow muscles has been extensively studied, it is still not fully understood. Here, we propose that nicotinic acetylcholine receptors (AChRs) expressed in slow muscles of zebrafish have high Ca2+ permeability compared to that of AChRs of fast muscles. To analyse the significance of the Ca2+ influx through AChRs in slow muscles, we generated a transgenic (Tg) zebrafish line that expresses Ca2+-impermeable AChRs in its slow muscles. The locomotor activities of the Tg zebrafish were markedly decreased at 1–3 days post-fertilization (dpf) compared to those of zebrafish expressing Ca2+-permeable AChRs in their slow muscles. Ca2+ imaging suggested that Ca2+ influx via AChRs is crucial for the Ca2+ response during muscle contraction in 2 dpf larvae, as slow muscle cells of the Tg line lacked a sustained Ca2+ response. Furthermore, we found that slow muscles of the Tg line became thinner compared to those expressing Ca2+-permeable AChRs. These short Ca2+ responses and thinner slow muscles may have induced locomotion impairment in the Tg line. These results suggested the physiological roles of the Ca2+ influx through AChRs in slow muscles and provided new insights into the characterization of fast and slow muscles.