Identification of Vesicular Monoamine Transporter 2 (vmat2)‐Containing O 2 Chemoreceptors in the Gills of Zebrafish

All vertebrates “sense” changes in oxygen (O 2 ) via specialized cells, called chemoreceptors, associated with the peripheral nervous system. Aquatic vertebrates are especially prone to fluctuations in environmental O 2 levels. Thus it is essential for them to readily detect low O 2 and make appropriate ventilatory adjustments. Teleost species, such as zebrafish, have O 2 chemoreceptive neuroepithelial cells (NECs) embedded in the gill epithelium. These cells exhibit membrane depolarization and vesicular recycling upon exposure to hypoxia, and express the monoamine neurotransmitter, serotonin (5‐HT). Our research objectives are to identify gill O 2 chemoreceptors in live tissue preparations and determine the role of intracellular Ca 2+ in O 2 sensing. We are currently employing a transgenic zebrafish line, expressing green fluorescent protein (GFP) under the control of vesicular monoamine transporter 2 (vmat2) regulatory elements, in order to identify NECs and characterize their hypoxic responses in vitro and in situ . Immunohistochemistry and confocal microscopy were used to determine the distribution and identity of GFP‐positive cells in gills. Our results show that the population of GFP‐positive cells in our transgenic line significantly overlaps with serotonergic NECs in the gill filaments. Preliminary studies using fura 2‐based imaging indicate that isolated GFP‐positive cells stimulated by hypoxia undergo an increase in intracellular Ca 2+ concentration. Identification of NECs both in vitro and in situ using a vital marker will have a great impact on future work addressing the physiological properties of these cells. Support or Funding Information This research project is funded by Natural Sciences and Engineering Research Council of Canada (NSERC).