The water channel aquaporin-1a1 facilitates movement of CO2 and ammonia in zebrafish (Danio rerio) larvae

Abstract

The present study tested the hypothesis that zebrafish (Danio rerio) aquaporin-1a1 (AQP1a1) serves as a multi-functional channel for the transfer of the small gaseous molecules, CO 2 and ammonia, as well as water, across biological membranes. Zebrafish embryos were microinjected with a translation-blocking morpholino oligonucleotide targeted to AQP1a1. Knockdown of AQP1a1 significantly reduced rates of CO 2 and ammonia excretion, as well as water fluxes, in larvae at 4 days post fertilization (dpf ). Because AQP1a1 is expressed both in ionocytes present on the body surface and in red blood cells, the haemolytic agent phenylhydrazine was used to distinguish between the contributions of AQP1a1 to gas transfer in these two locations. Phenylhydrazine treatment had no effect on AQP1a1-linked excretion of CO 2 or ammonia, providing evidence that AQP1a1 localized to the yolk sac epithelium, rather than red blood cell AQP1a1, is the major site of CO 2 and ammonia movements. The possibility that AQP1a1 and the rhesus glycoprotein Rhcg1, which also serves as a dual CO 2 and ammonia channel, act in concert to facilitate CO 2 and ammonia excretion was explored. Although knockdown of each protein did not affect the abundance of mRNA and protein of the other protein under control conditions, impairment of ammonia excretion by chronic exposure to high external ammonia triggered a significant increase in the abundance of AQP1a1 mRNA and protein in 4 dpf larvae experiencing Rhcg1 knockdown. Collectively, these results suggest that AQP1a1 in zebrafish larvae facilitates the movement of CO 2 and ammonia, as well as water, in a physiologically relevant fashion.

Identification of the role of Rh protein in ammonia excretion of swimming crab Portunus trituberculatus

“…In the present study, the increase in mRNA expression level of AQP suggests that AQP serves as a NH 3 channel, synergized with Rh protein to facilitate ammonia excretion. A similar report appeared for zebrafish Danio rerio, where exposure to high external ammonia resulted in significantly higher AQP1a1 mRNA and protein abundance in Rhcg1-knockdown larvae (Talbot et al, 2015). Theoretical considerations argued that NH 4 + in the hemolymph may substitute for K + via a K + channel and NKA, and transport NH 4 + across the basolateral membrane into the epithelial cells (Choe et al, 2000;Wood et al, 2013).…”

Transport and Use of Bicarbonate in Plants: Current Knowledge and Challenges Ahead

“…CO 2 crosses biological membranes by diffusion either through the lipid bilayer or through pores. A subset of aquaporins and related proteins [ 15 , 16 ] can behave as CO 2 channels [ 17 ]. Models based on artificial lipid bilayers indicated that the resistance for CO 2 diffusion is small and mostly limited by unstirred layers.…”

CO2 Permeability of Biological Membranes and Role of CO2 Channels

“…Plant aquaporin-mediated CO 2 transport has been implicated in several plant functions and importantly in plant growth [ 49 , 54 , 55 , 56 ]. Similarly, Perry and Gilmour and colleagues [ 52 , 53 ] have shown that the central function of the gills of zebrafish, or skin in larvae, to excrete ammonia and CO 2 is greatly supported by CO 2 /NH 3 channels.…”

“…The conclusion was that the Rh proteins are channels for both CO 2 and NH 3 , which agrees with the competition between CO 2 and NH 3 , as demonstrated by Endeward et al [ 6 ] for RhAG of the human red cell membrane. Later, the same group [ 53 ] showed that the zebrafish aquaporin-1a1 exhibits an analogous dual role as gas channel for both CO 2 and NH 3 . Morpholino knockdown of AQP-1a1 protein expression in zebrafish larvae, while not affecting oxygen uptake of the larvae, reduced their CO 2 release as well as their ammonia efflux, in addition to reducing their exchange of water.…”

“…Morpholino knockdown of AQP-1a1 protein expression in zebrafish larvae, while not affecting oxygen uptake of the larvae, reduced their CO 2 release as well as their ammonia efflux, in addition to reducing their exchange of water. Talbot et al [ 53 ] suggest that the localization of AQP-1a1 in the yolk sac epithelium rather than its localization in RBCs is the crucial one for the transport of the two gases in the early stages of zebrafish development.…”