ORCID Profile
0000-0002-8327-9224
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Publisher: The Company of Biologists
Date: 2020
DOI: 10.1242/JEB.210732
Abstract: Estuarine crocodiles Crocodylus porosus inhabit freshwater, estuarine and marine environments. Despite being known to undertake extensive movements throughout and between hypo- and hyperosmotic environments, little is known on the role of the cloaca in coping with changes in salinity. In addition to the well-documented functional plasticity of the lingual salt glands, we report here that the middle of the three cloacal segments (i.e. the urodaeum), responds to increased ambient salinity to enhance solute-coupled water absorption. This post-renal modification of urine serves to conserve water when exposed to hyperosmotic environments and, in conjunction with lingual salt gland secretions, enables C. porosus to maintain salt and water balance and thereby thrive in hyperosmotic environments. Isolated epithelia from the urodaeum of 70% seawater-acclimated C. porosus had a strongly enhanced short circuit current (indicator of active ion transport) compared to freshwater-acclimated crocodiles. This enhanced active ion absorption was driven by increased Na+/K+-ATPase activity, and possibly enhanced proton pump activity, and was facilitated by the apical epithelial Na+ channel (ENaC) and/or the apical Na+/H+ exchanger (NHE2), both of which are expressed in the urodaeum. NHE3 was expressed at very low levels in the urodaeum and likely does not contribute to solute-coupled water absorption in this cloacal segment. Since C. porosus does not appear to drink water of salinities above 18 ppt, observations of elevated short circuit current in the rectum as well as a trend for increased NHE2 expression in the esophagus, the anterior intestine, and the rectum, suggests that dietary salt intake may stimulate salt, and possibly water absorption by the gastro-intestinal tract of C. porosus living in hyperosmotic environments.
Publisher: Springer Science and Business Media LLC
Date: 21-10-2020
Publisher: Springer Science and Business Media LLC
Date: 13-09-2016
DOI: 10.1038/SREP33216
Abstract: Neurosensory and behavioural disruptions are some of the most consistently reported responses upon exposure to ocean acidification-relevant CO 2 levels, especially in coral reef fishes. The underlying cause of these disruptions is thought to be altered current across the GABA A receptor in neuronal cells due to changes in ion gradients (HCO 3 − and/or Cl − ) that occur in the body following compensation for elevated ambient CO 2 . Despite these widely-documented behavioural disruptions, the present study is the first to pair a behavioural assay with measurements of relevant intracellular and extracellular acid-base parameters in a coral reef fish exposed to elevated CO 2 . Spiny damselfish ( Acanthochromis polyacanthus ) exposed to 1900 μatm CO 2 for 4 days exhibited significantly increased intracellular and extracellular HCO 3 − concentrations and elevated brain pH i compared to control fish, providing evidence of CO 2 compensation. As expected, high CO 2 exposed damselfish spent significantly more time in a chemical alarm cue (CAC) than control fish, supporting a potential link between behavioural disruption and CO 2 compensation. Using HCO 3 − measurements from the damselfish, the reversal potential for GABA A ( E GABA ) was calculated, illustrating that biophysical properties of the brain during CO 2 compensation could change GABA A receptor function and account for the behavioural disturbances noted during exposure to elevated CO 2 .
No related grants have been discovered for Rachael Heuer.