Guanylin peptides regulate electrolyte and fluid transport in the Gulf toadfish (Opsanus beta) posterior intestine

The physiological effects of guanylin (GN) and uroguanylin (UGN) on fluid and electrolyte transport in the teleost fish intestine have yet to be thoroughly investigated. In the present study, the effects of GN, UGN, and renoguanylin (RGN; a GN and UGN homolog) on short-circuit current ( Isc) and the transport of Cl−, Na+, bicarbonate (HCO3−), and fluid in the Gulf toadfish ( Opsanus beta) intestine were determined using Ussing chambers, pH-stat titration, and intestinal sac experiments. GN, UGN, and RGN reversed the Isc of the posterior intestine (absorptive-to-secretory), but not of the anterior intestine. RGN decreased baseline HCO3− secretion, but increased Cl− and fluid secretion in the posterior intestine. The secretory response of the posterior intestine coincides with the presence of basolateral NKCC1 and apical cystic fibrosis transmembrane conductance regulator (CFTR), the latter of which is lacking in the anterior intestine and is not permeable to HCO3− in the posterior intestine. However, the response to RGN by the posterior intestine is counterintuitive given the known role of the marine teleost intestine as a salt- and water-absorbing organ. These data demonstrate that marine teleosts possess a tissue-specific secretory response, apparently associated with seawater adaptation, the exact role of which remains to be determined.

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The role of the rectum in osmoregulation and the potential effect of renoguanylin on SLC26a6 transport activity in the Gulf toadfish (Opsanus beta)

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00033.2016 ◽

2016 ◽

Vol 311 (1) ◽

pp. R179-R191 ◽

Cited By ~ 6

Author(s):

Ilan M. Ruhr ◽

Yoshio Takei ◽

Martin Grosell

Keyword(s):

Water Absorption ◽

Short Circuit ◽

Short Circuit Current ◽

Potential Effect ◽

Posterior Intestine ◽

Distal Intestine ◽

Opsanus Beta ◽

Ion Absorption ◽

Gulf Toadfish

Teleosts living in seawater continually absorb water across the intestine to compensate for branchial water loss to the environment. The present study reveals that the Gulf toadfish ( Opsanus beta) rectum plays a comparable role to the posterior intestine in ion and water absorption. However, the posterior intestine appears to rely more on SLC26a6 (a HCO3−/Cl− antiporter) and the rectum appears to rely on NKCC2 (SLC12a1) for the purposes of solute-coupled water absorption. The present study also demonstrates that the rectum responds to renoguanylin (RGN), a member of the guanylin family of peptides that alters the normal osmoregulatory processes of the distal intestine, by inhibited water absorption. RGN decreases rectal water absorption more greatly than in the posterior intestine and leads to net Na+ and Cl− secretion, and a reversal of the absorptive short-circuit current ( ISC). It is hypothesized that maintaining a larger fluid volume within the distal segments of intestinal tract facilitates the removal of CaCO3 precipitates and other solids from the intestine. Indeed, the expression of the components of the Cl−-secretory response, apical CFTR, and basolateral NKCC1 (SLC12a2), are upregulated in the rectum of the Gulf toadfish after 96 h in 60 ppt, an exposure that increases CaCO3 precipitate formation relative to 35 ppt. Moreover, the downstream intracellular effects of RGN appear to directly inhibit ion absorption by NKCC2 and anion exchange by SLC26a6. Overall, the present findings elucidate key electrophysiological differences between the posterior intestine and rectum of Gulf toadfish and the potent regulatory role renoguanylin plays in osmoregulation.

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The differential role of renoguanylin in osmoregulation and apical Cl−/HCO3− exchange activity in the posterior intestine of the Gulf toadfish (Opsanus beta)

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00118.2015 ◽

2015 ◽

Vol 309 (4) ◽

pp. R399-R409 ◽

Cited By ~ 6

Author(s):

Ilan M. Ruhr ◽

Edward M. Mager ◽

Yoshio Takei ◽

Martin Grosell

Keyword(s):

Secretory Pathway ◽

Short Circuit ◽

Short Circuit Current ◽

Fluid Absorption ◽

Posterior Intestine ◽

Opsanus Beta ◽

Intestinal Physiology ◽

Peptide System ◽

Exchange Activity ◽

Gulf Toadfish

The guanylin family of peptides are effective regulators of intestinal physiology in marine teleosts. In the distal intestinal segments, they inhibit or reverse fluid absorption by inhibiting the absorptive short-circuit current ( Isc). The present findings demonstrate that mRNA from guanylin and uroguanylin, as well as at least one isoform of the guanylin peptide receptor, apical guanylyl cyclase-C (GC-C), was highly expressed in the intestine and rectum of the Gulf toadfish ( Opsanus beta). In the posterior intestine, GC-C, as well as the cystic fibrosis transmembrane conductance regulator and basolateral Na+/K+/2Cl− cotransporter, which comprise a Cl−-secretory pathway, were transcriptionally upregulated in 60 parts per thousand (ppt). The present study also shows that, in intestinal tissues from Gulf toadfish held in 35 ppt, renoguanylin (RGN) expectedly causes net Cl− secretion, inhibits both the absorptive Isc and fluid absorption, and decreases HCO3− secretion. Likewise, in intestinal tissues from Gulf toadfish acclimated to 60 ppt, RGN also inhibits the absorptive Isc and fluid absorption but to an even greater extent, corresponding with the mRNA expression data. In contrast, RGN does not alter Cl− flux and, instead, elevates HCO3− secretion in the 60-ppt group, suggesting increased apical Cl−/HCO3− exchange activity by SLC26a6. Overall, these findings reinforce the hypotheses that the guanylin peptide system is important for salinity acclimatization and that the secretory response could facilitate the removal of solids, such as CaCO3 precipitates, from the intestine.

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The role of uptake and degradation in the regulation of peripheral serotonin dynamics in Gulf toadfish, Opsanus beta

Comparative Biochemistry and Physiology Part A Molecular & Integrative Physiology ◽

10.1016/j.cbpa.2021.110980 ◽

2021 ◽

pp. 110980

Author(s):

John Sebastiani ◽

M. Danielle McDonald

Keyword(s):

Opsanus Beta ◽

Gulf Toadfish

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Protein kinase C potentiates cAMP-stimulated mouse duodenal mucosal bicarbonate secretion in vitro

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00251.2003 ◽

2004 ◽

Vol 286 (5) ◽

pp. G814-G821 ◽

Cited By ~ 10

Author(s):

Bi-Guang Tuo ◽

Jimmy Y. C. Chow ◽

Kim E. Barrett ◽

Jon I. Isenberg

Keyword(s):

Short Circuit ◽

Short Circuit Current ◽

Duodenal Mucosa ◽

Bicarbonate Secretion ◽

Dependent Manner ◽

Concentration Dependent Manner ◽

Ussing Chambers ◽

Duodenal Bicarbonate Secretion

PKC has been shown to regulate epithelial Cl- secretion in a variety of models. However, the role of PKC in duodenal mucosal bicarbonate secretion is less clear. We aimed to investigate the role of PKC in regulation of duodenal mucosal bicarbonate secretion. Bicarbonate secretion by murine duodenal mucosa was examined in vitro in Ussing chambers using a pH-stat technique. PKC isoform expression and activity were assessed by Western blotting and in vitro kinase assays, respectively. PMA (an activator of PKC) alone had no effect on duodenal bicarbonate secretion or short-circuit current ( Isc). When PMA and dibutyryl-cAMP (db-cAMP) were added simultaneously, PMA failed to alter db-cAMP-stimulated duodenal bicarbonate secretion or Isc ( P > 0.05). However, a 1-h preincubation with PMA potentiated db-cAMP-stimulated duodenal bicarbonate secretion and Isc in a concentration-dependent manner (from 10-8 to 10-5M) ( P < 0.05). PMA preincubation had no effects on carbachol- or heat-stable toxin-stimulated bicarbonate secretion. Western blot analysis revealed that PKCα, -γ, -ϵ, -θ, -μ, and -ι/λ were expressed in murine duodenal mucosa. Ro 31–8220 (an inhibitor active against PKCϵ, -α, -β, and -γ), but not Gö 6983 (an inhibitor active against PKCα, -γ, -β, and -δ), reversed the potentiating effect of PMA on db-cAMP-stimulated bicarbonate secretion. PMA also time- and concentration-dependently increased the activity of PKCϵ, an effect that was prevented by Ro 31–8220 but not Gö 6983. These results demonstrate that activation of PKC potentiates cAMP-stimulated duodenal bicarbonate secretion, whereas it does not modify basal secretion. The effect of PKC on cAMP-stimulated bicarbonate secretion is mediated by the PKCϵ isoform.

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Campylobacter jejuni inhibits the absorptive transport functions of Caco-2 cells and disrupts cellular tight junctions

Microbiology ◽

10.1099/mic.0.27950-0 ◽

2005 ◽

Vol 151 (7) ◽

pp. 2451-2458 ◽

Cited By ~ 61

Author(s):

Amanda MacCallum ◽

Simon P. Hardy ◽

Paul H. Everest

Keyword(s):

Tight Junction ◽

Tight Junctions ◽

Campylobacter Jejuni ◽

Fluid Transport ◽

Cell Function ◽

Short Circuit ◽

Short Circuit Current ◽

Ussing Chambers ◽

Cell Monolayers ◽

Junction Protein

Caco-2 cells are models of absorptive enterocytes. The net transport of fluid from apical to basolateral surfaces results in ‘domes' forming in differentiated monolayers. Here, the effect of Campylobacter jejuni on this process has been examined. C. jejuni caused no changes in short-circuit current upon infection of Caco-2 cell monolayers in Ussing chambers. Thus, no active secretory events could be demonstrated using this model. It was therefore hypothesized that C. jejuni could inhibit the absorptive function of enterocytes and that this may contribute to diarrhoeal disease. C. jejuni infection of fluid-transporting (‘doming’) Caco-2 cells resulted in a significant reduction in dome number, which correlated with a decrease in tight junction integrity in infected monolayers, when measured as transepithelial electrical resistance. Defined mutants of C. jejuni also reduced dome numbers in infected monolayers. C. jejuni also altered the distribution of the tight junction protein occludin within cell monolayers. The addition to monolayers of extracellular gentamicin prevented these changes, indicating the contribution of extracellular bacteria to this process. Thus, tight junction integrity is required for fluid transport in Caco-2 cell monolayers as leaky tight junctions cannot maintain support of transported fluid at the basolateral surface of infected cell monolayers. Inhibition of absorptive cell function, changes in epithelial resistance and rearrangement of tight junctional proteins such as occludin represent a potential diarrhoeal mechanism of C. jejuni.

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Prostaglandin-induced recovery of barrier function in porcine ileum is triggered by chloride secretion

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1999.276.1.g28 ◽

1999 ◽

Vol 276 (1) ◽

pp. G28-G36 ◽

Cited By ~ 24

Author(s):

Anthony T. Blikslager ◽

Malcolm C. Roberts ◽

Robert A. Argenzio

Keyword(s):

Short Circuit ◽

Second Messengers ◽

Short Circuit Current ◽

Chloride Secretion ◽

Ringer Solution ◽

Signal Recovery ◽

Osmotic Gradient ◽

Current Increase ◽

Ussing Chambers

We have previously shown that PGI2 and PGE2 have a synergistic role in restoring electrical transepithelial resistance ( R) in ischemia-injured porcine ileum via the second messengers Ca2+ and cAMP. Because Ca2+ and cAMP stimulate Cl− secretion, we assessed the role of PG-induced Cl−secretion in recovery of R. Mucosa from porcine ileum subjected to ischemia for 45 min was mounted in Ussing chambers and bathed in indomethacin and Ringer solution. Addition of PGs stimulated a twofold increase in R, which was preceded by elevations in short-circuit current (increase of 25 μA/cm2). The PG-induced effect on R was partially inhibited with bumetanide, an inhibitor of Cl− secretion. The remaining elevations in R were similar in magnitude to those induced in ischemic tissues by amiloride, an inhibitor of Na+ absorption. Treatment with 10−4 M 8-bromo-cGMP or 300 mosM mucosal urea resulted in elevations in R similar to those attained with PG treatment. PGs signal recovery of Rvia induction of Cl−secretion and inhibition of Na+absorption, possibly by establishing a transmucosal osmotic gradient.

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Decreased electrogenic anionic secretory response in the porcine colon following in vivo challenge withBrachyspiraspp. supports an altered mucin environment

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00348.2018 ◽

2019 ◽

Vol 316 (4) ◽

pp. G495-G508 ◽

Cited By ~ 3

Author(s):

Cole B. Enns ◽

John C. S. Harding ◽

Matthew E. Loewen

Keyword(s):

Cystic Fibrosis ◽

Mrna Expression ◽

Rheological Properties ◽

Diarrheal Disease ◽

Short Circuit ◽

Anion Channel ◽

Secretory Response ◽

Secretory Function ◽

Ussing Chambers

Brachyspira spp. cause diarrheal disease in multiple animal species by colonization of the colon, resulting in colitis, mucus induction, and disrupted ion transport. Unique to spirochete pathogenesis is the immense production of mucus, resulting in a niche mucin environment likely favoring spirochete colonization. Mucin rheological properties are heavily influenced by anionic secretion, and loss of secretory function has been implicated in diseases such as cystic fibrosis. Here, the effects on the agonist-induced electrogenic anionic secretory response by infectious colonic spirochete bacteria Brachyspira hyodysenteriae and Brachyspira hampsonii were assessed in the proximal, apex, and distal sections of colon in Ussing chambers. Activation of secretion via isoproterenol, carbachol, and forskolin/3-isobutyl-1-methylxanthine demonstrated a significantly decreased change in short-circuit current ( Isc) in Brachyspira-infected pigs in all sections. Tissue resistances did not account for this difference, rather, it was attributed to a decrease in anionic secretion as indicated by a decrease in bumetanide inhibitable Isc. Quantitative RT-PCR and Western blot analyses determined that the major anionic channels of the epithelium were downregulated in diarrheic pigs paired with altered mucin gene expression. The investigated cytokines were not responsible for the downregulation of anion channel gene transcripts. Although IL-1α was upregulated in all segments, it did not alter cystic fibrosis transmembrane conductance regulator (CFTR) mRNA expression in Caco-2 monolayers. However, a whole cell Brachyspira hampsonii lysate significantly reduced CFTR mRNA expression in Caco-2 monolayers. Together, these findings indicate that these two Brachyspira spp. may directly cause a decreased anionic secretory response in the porcine colon, supporting an altered mucin environment likely favoring spirochete colonization.NEW & NOTEWORTHY This research demonstrates for the first time that the niche mucin environment produced by two infectious spirochete spp. is supported by a decrease in the electrogenic anionic secretory response throughout the porcine colon. Our findings suggest that the host’s cytokine response is not likely responsible for the decrease in anionic secretory function. Rather, it appears that Brachyspira spp. directly impede ion channel transcription and translation, potentially altering colonic mucin rheological properties, which may favor spirochete colonization.

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Prostaglandin-mediated inhibition of Na+/H+ exchanger isoform 2 stimulates recovery of barrier function in ischemia-injured intestine

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00380.2005 ◽

2006 ◽

Vol 291 (5) ◽

pp. G885-G894 ◽

Cited By ~ 31

Author(s):

Adam J. Moeser ◽

Prashant K. Nighot ◽

Kathleen A. Ryan ◽

Jenna G. Wooten ◽

Anthony T. Blikslager

Keyword(s):

Barrier Function ◽

Intestinal Ischemia ◽

Short Circuit ◽

Intestinal Barrier ◽

Short Circuit Current ◽

Selective Inhibition ◽

Ileal Mucosa ◽

Ussing Chambers ◽

Nhe Isoforms

Prostaglandins stimulate repair of the ischemia-injured intestinal barrier in the porcine ileum through a mechanism involving cAMP-dependent Cl− secretion and inhibition of electroneutral Na+/H+ exchanger (NHE) activity. In the present study, we focused on the role of individual NHE isoforms in the recovery of barrier function. Ischemia-injured porcine ileal mucosa was mounted on Ussing chambers. Short-circuit current ( Isc), transepithelial electrical resistance (TER), and isotopic fluxes of 22Na were measured in response to PGE2 and selective inhibitors of epithelial NHE isoforms. Immunoassays were used to assess the expression of NHE isoforms. Forty-five minutes of intestinal ischemia resulted in a 45% reduction in TER ( P < 0.01). Near-complete restitution occurred within 60 min. Inhibition of NHE2 with HOE-694 (25 μM) added to the mucosal surface of the injured ileum stimulated significant elevations in TER, independent of changes in Isc and histological evidence of restitution. Pharmacological inhibition of NHE3 or NHE1 with mucosal S-3226 (20 μM) or serosal cariporide (25 μM), respectively, had no effect. Ischemia-injured tissues treated with mucosal S-3226 or HOE-694 exhibited equivalent reductions in mucosal-to-serosal fluxes of 22Na+ (by ∼35%) compared with nontreated ischemia-injured control tissues ( P < 0.05). Intestinal ischemia resulted in increased expression of the cytoplasmic NHE regulatory factor EBP50 in NHE2 but not in NHE3 immunoprecipitates. Selective inhibition of NHE2, and not NHE3, induces recovery of barrier function in the ischemia-injured intestine.

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Taurodeoxycholate and the developing rabbit distal colon: absence of secretory effect

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1987.253.4.g483 ◽

1987 ◽

Vol 253 (4) ◽

pp. G483-G488 ◽

Cited By ~ 4

Author(s):

G. D. Potter ◽

R. Lester ◽

S. M. Burlingame ◽

P. A. Mitchell ◽

K. L. Schmidt

Keyword(s):

Ion Transport ◽

Bile Acids ◽

Phorbol Ester ◽

Short Circuit ◽

Short Circuit Current ◽

Distal Colon ◽

Fluid Secretion ◽

Secretory Response ◽

Ussing Chambers ◽

Cl Secretion

Failure to absorb bile acids by the ileum leads to fluid secretion by the colon and diarrhea in adults. The infant ileum, however, does not actively transport bile acids. Therefore, we investigated the effect of taurodeoxycholic acid (TDCA) on ion transport in the colon of rabbits 7-10 days old. We mounted distal colon from infant and adult rabbits in modified Ussing chambers and exposed the mucosal or serosal surfaces to TDCA. In the adult, 50 microM TDCA produced an increase in short-circuit current (delta Isc = 1.0 +/- 0.3 mu eq . h-1 . cm-2, P less than 0.05) and Cl secretion. In the infant, the effect was different, Isc was reduced (delta Isc = -1.1 +/- 0.2 mu eq . h-1 . cm-2, P less than 0.01) and ion flux was not altered. Microscopy demonstrated that the infant epithelium was not significantly damaged by exposure to TDCA at these concentrations. The infant colon was, however, capable of a secretory response to a variety of agonists including theophylline, carbachol, bradykinin, serotonin, and 12,13-dibutyryl phorbol ester. The infant rabbit distal colon lacks a secretory response to TDCA during that period when the ileum cannot transport bile acids.

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