Occludin and hydromineral balance in Xenopus laevis

A recent study demonstrated that in response to a feeding-induced metabolic acidosis, goldfish (Carassius auratus) adjust epithelial protein and/or mRNA expression in their kidney tubules for multiple transporters known to be relevant for acid-base regulation. These include Na + /H + exchanger (NHE), V-type H + -ATPase (V-ATPase), cytoplasmic carbonic anhydrase, HCO 3 − transporters and Rhesus proteins. Consequently, renal acid output in the form of protons and NH 4 + increases. However, little is known about the mechanistic details of renal acid-base regulation in C. auratus and teleost fishes in general. The present study applied the scanning ion-selective electrode technique (SIET) to measure proton flux in proximal, distal and connecting tubules of goldfish. We detected increased H + efflux into the extracellular fluid from the tubule in fed animals, resulting from paracellular back-flux of H + through the tight junction. By applying inhibitors for selected acid-base regulatory epithelial transporters, we found that cytosolic carbonic anhydrase and HCO 3 − transporters were important in mediating H + flux in all three tubule segments of fed goldfish. Contrastingly, V-ATPase seemed to play a role in H + flux only in proximal and distal tubules, and NHE in proximal and connecting tubules. We developed working models for transport of acid-base relevant equivalents (H + , HCO 3 − , NH 3 /NH 4 + ) for each tubule segment in C. auratus kidney. While the proximal tubule appears to play a major role in both H + secretion and HCO 3 − reabsorption, the distal and connecting tubules seem to mainly serve for HCO 3 − reabsorption and NH 3 /NH 4 + secretion.

Section: General Observationsmentioning

confidence: 90%

Section-specific H+ fluxes in renal tubules of fasted and fed goldfish

Fehsenfeld

Kolosov

Wood

2019

“…Ocln is regarded to be an important TJ protein in epithelial barriers (Yu et al, 2005). In Xenopus, Ocln has been shown to exhibit spatial differences in tissue localization that relate to the resistance of epithelia, as well as organ-specific alterations in abundance following changes in the salt content of their surroundings (Chasiotis and Kelly, 2009). Additionally, Ocln is known to undergo post-transcriptional/translational modifications in vertebrates, which remove it from the TJ complex (reviewed in Cummins, 2012).…”

Section: Effect Of Bd Infection On Cldn-1 Ocln and Tric Abundancementioning

confidence: 99%

“…Cldn-1, Ocln, ZO-1), have been shown to respond to changes in environmental conditions (Castillo et al, 1991;Chasiotis and Kelly, 2009;Tokuda et al, 2010). Over 30 genes encoding amphibian TJ proteins have now been reported, yet little is known about their contribution to TJ permeability (Cardellini et al, 1996;Cordenonsi et al, 1997;Fesenko et al, 2000;Klein et al, 2002;Chasiotis and Kelly, 2009;Chang et al, 2010;Saharinen et al, 2010;Yamagishi et al, 2010;Baltzegar et al, 2013;Sun et al, 2015). In addition, the majority of these genes have been identified in the strictly aquatic anurans Xenopus laevis and Xenopus tropicalis; thus, almost nothing is known about the characteristics of TJ proteins in terrestrial and semi-aquatic amphibians (Günzel and Yu, 2013).…”

Section: Introductionmentioning

confidence: 99%

A lethal fungal pathogen directly alters tight junction proteins in the skin of a susceptible amphibian

Gauberg

Cramp

et al. 2018

Bacterial and viral pathogens can weaken epithelial barriers by targeting and disrupting tight junction (TJ) proteins. However, comparatively little is known about the direct effects of fungal pathogens on TJ proteins and their expression. The disease chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), is threatening amphibian populations worldwide. Bd is known to infect amphibian skin and disrupt cutaneous osmoregulation. However, exactly how this occurs is poorly understood. This study considered the impact of Bd infection on the barrier properties of the Australian green tree frog (Litoria caerulea) epidermis by examining how inoculation of animals with Bd influenced the paracellular movement of FITC-dextran (4 kDa, FD-4) across the skin in association with alterations in the mRNA and protein abundance of select TJ proteins of the epidermal TJ complex. It was observed that Bd infection increased paracellular movement of FD-4 across the skin linearly with fungal infection load. In addition, Bd infection increased transcript abundance of the tricellular TJ (tTJ) protein tricellulin (Tric) as well as the bicellular TJ (bTJ) proteins occludin (Ocln), claudin (Cldn)-1, Cldn-4 and the scaffolding TJ protein zonula occludens 1 (ZO-1). However, while Tric protein abundance increased in accord with changes in transcript abundance, protein abundance of Cldn-1 was significantly reduced and Ocln protein abundance was unchanged. Data indicate that disruption of cutaneous osmoregulation in L. caerulea following Bd infection occurs, at least in part, by an increase in epidermal paracellular permeability in association with compromised integrity of the epidermal TJ complex.

“…In this regard, the effects of environmental salinity on the permeability of intestinal epithelia in aquatic vertebrates such as fishes are well documented (see Marshall and Grosell, 2005). In addition, increased permeability of the anterior intestinal epithelium following FW to BW acclimation (without alteration in active transcellular transport processes) has also been suggested to occur in amphibians (Chasiotis and Kelly, 2009). The physiological consequences of decreased NKA and VA activity in the PMG of larval C. riparius in response to IPW rearing are unclear (see Fig.2C, Fig.3C).…”

Section: Differences In Nka and Va Activity In Different Rearing Envimentioning

confidence: 99%

Tissue specific ionomotive enzyme activity and K+ reabsorption reveal the rectum as an important ionoregulatory organ in larvalChironomous ripariusexposed to varying salinity

Jonusaite

Kelly

Donini

2013

Self Cite

Summary A role for the rectum in the ionoregulatory homeostasis of larval Chironomus riparius was revealed by rearing animals in different saline environments and examining: (1) the spatial distribution and activity of keystone ionomotive enzymes Na+-K+-ATPase (NKA) and V-type H+-ATPase (VA) in the alimentary canal and (2) rectal K+ transport with scanning ion-selective electrode technique (SIET). NKA and VA activity were measured in four distinct regions of the alimentary canal as follows: the combined foregut and anterior midgut (FAMG), the posterior midgut (PMG), the Malpighian tubules (MT) and the hindgut (HG). Both enzymes exhibited 10 - 20 times greater activity in the HG relative to all other areas. When larvae were reared in either ion-poor water (IPW) or freshwater (FW), no significant difference in HG enzyme activity was observed. However, in brackish water (BW) reared animals, NKA and VA activity in the HG significantly decreased. Immunolocalization of NKA and VA in the HG revealed that the bulk of protein was located in the rectum. Therefore K+ transport across the rectum was examined using SIET. Measurement of K+ flux along the rectum revealed a net K+ reabsorption which was reduced four-fold in BW-reared larvae versus larvae reared in FW or IPW. Inhibition of NKA with ouabain, VA with bafilomycin and K+ channels with charybdotoxin, diminished rectal K+ reabsorption in FW- and IPW-reared larvae, but not BW-reared larvae. Data suggest that the rectum of C. riparius plays an important role in allowing these larvae to cope with dilute as well as salinated environmental conditions.