Esophageal desalination of seawater in flounder: role of active sodium transport

Parmelee, Judith T.; Renfro, J. Larry

doi:10.1152/ajpregu.1983.245.6.r888

Cited by 48 publications

(60 citation statements)

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“…In species examined to date, the majority of HCO 3 -secreted by the apical anion exchange process is derived from hydration of metabolic CO 2 with the resulting H + being extruded via a Na although the cellular mechanisms remain to be fully elucidated. The esophageal absorption of salt combined with a limited water permeability (Hirano and Mayer-Gostan, 1976;Parmelee and Renfro, 1983) of this gastro-intestinal segment results in a reduction of osmotic pressure in the fluids entering the anterior portion of the intestine (Marshall and Grosell, 2005). This reduction in osmotic pressure allows for fluid absorption by the more distal segments of the gastro-intestinal tract.…”

Section: Osmoregulation In Marine Fishmentioning

confidence: 99%

“…In general, Cl -concentrations exceed Na + concentrations in seawater by ~70·mmol·l -1 , which means that seawater ingestion results in higher gastrointestinal intake of Cl -than Na + . Further, desalinization in the esophagus occurs via both passive and active equimolar Na + and Cl -absorption (Kirsch and Meister, 1982;Parmelee and Renfro, 1983;Smith, 1930;Wilson et al, 1996). With little or no transport across the gastric mucosa in starved fish, the consequence of the higher concentrations of Cl -than Na + in seawater and equal molar Na + and Cl -absorption in the esophagus is that fluids entering the intestine contain higher concentrations of Cl -than Na + .…”

Section: In Vitro Versus In Vivo Discrepanciesmentioning

confidence: 99%

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Intestinal anion exchange in marine fish osmoregulation

Grosell

2006

Journal of Experimental Biology

231

211

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Osmoregulation in marine fishThree distinct strategies for maintaining salt and water balance have evolved in fishes inhabiting the marine environments. (1) Osmoconformity/ionoconformity is found in the strictly marine agnathan hagfishes, which do not appear to regulate osmotic pressure and concentrations of main osmolytes to a great extent in seawater (Morris, 1958). (2) Osmoconformity and ionoregulation are seen in marine elasmobranchs (Hazon et al., 2003) and in the lobe-finned coelacanth (Griffith et al., 1974), which maintains plasma osmolality at or slightly above that of the surrounding seawater but NaCl concentrations at approximately d of ambient levels. (3) The most common strategy is osmoregulation, found in all teleosts (Marshall and Grosell, 2005) and marine lampreys (Morris, 1958), achieved by the regulation of the main extracellular electrolyte (Na + and Cl -) levels at approximately d of full strength seawater. Under steady state conditions at constant salinities, hagfish, elasmobranchs and coelacanths presumably do not need to drink to maintain water balance. It was shown, however, that the unavoidable renal and extra-renal fluid loss to the hypertonic marine environment in hypo-osmoregulating fish was compensated for by ingestion of seawater with subsequent water absorption across the gastro-intestinal tract (Smith, 1930). More recently, it was demonstrated that even the osmoconforming elasmobranchs display transient drinking when exposed to elevated ambient salinity, and evidence for components of the rennin-angiotensin system (RAS), even in the elasmobranchs (Anderson et al., 2002;Hazon et al., 2003) and hagfish (Cobb et al., 2004) as well as in lamprey (Brown et al., 2005), continues to accumulate. The drinking reflex is at least in part controlled by RAS and it thus appears that the ability to regulate ingestion of seawater and thereby the magnitude of intestinal fluid absorption is an ancestral osmoregulatory trait among fishes.The ingestion and processing of the imbibed seawater for osmoregulatory purposes have, at least in teleost fish, received much attention for three quarters of a century since the first classic studies by Smith published in 1930(Smith, 1930. It is now well established that an initial desalinization of the ingested seawater occurs in the esophagus, which absorbs Na + and Cl -through both passive and active transport pathways, Despite early reports, dating back three quarters of a century, of high total CO 2 concentrations in the intestinal fluids of marine teleost fishes, only the past decade has provided some insight into the functional significance of this phenomenon. It is now being recognized that intestinal anion exchange is responsible for high luminal HCO 3 -and CO 3 2-concentrations while at the same time contributing substantially to intestinal Cl -and thereby water absorption, which is vital for marine fish osmoregulation. In species examined to date, the majority of HCO 3 -secreted by the apical anion exchange process is derived from hydration of metabolic ...

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Section: Osmoregulation In Marine Fishmentioning

confidence: 99%

Section: In Vitro Versus In Vivo Discrepanciesmentioning

confidence: 99%

Intestinal anion exchange in marine fish osmoregulation

Grosell

2006

Journal of Experimental Biology

231

211

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“…Water absorption by the intestine generates a high [SO 4 2Ϫ ] in the intestinal lumen (50-100 mM), and the steep concentration gradient promotes passive SO 4 2Ϫ absorption across the intestinal mucosa (34,60,62). Although passive SO 4 2Ϫ absorption dominates, an active secretory flux driven by an electroneutral brush-border SO 4 2Ϫ /Cl Ϫ exchanger is also present (62).…”

Section: ϫmentioning

confidence: 99%

Role of tubular secretion and carbonic anhydrase in vertebrate renal sulfate excretion

Pelis¹,

Renfro²

2004

American Journal of Physiology-Regulatory, Integrative and Comp

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/HCO 3 Ϫ exchange at the brushborder membrane, tubular carbonic anhydrase (CA) activity, CAII protein, and a proportion of tubular SO 4 2Ϫ secretion that is CA dependent. CA activity is required for about one-half of this net SO 4 2Ϫ secretion but is also required for about one-half of the net reabsorption in bird proximal epithelium. A CA-SO 4 2Ϫ /anion exchanger metabolon arrangement is proposed that may speed both the secretory and reabsorptive processes. renal proximal tubule; transport metabolon INORGANIC SO 4 2Ϫ IS THE SECOND most abundant anion in the sea and one of the most abundant anions in vertebrate plasma, with concentrations varying among species from 0.3 to 1.8 mM. This large tetrahedral divalent anion can be obtained from the diet (83) or oxidation of the sulfur-containing amino acids cysteine and methionine (77). Sulfoconjugation reactions are the initial detoxification process for many endogenous (e.g., steroid hormones) and xenobiotic compounds and are required for the activation of numerous biological molecules (e.g., heparin, cholecystokinin, and gastrin) (59). SO 4 2Ϫ is a major component of glycosaminoglycans (dermatan sulfate, chondroitin sulfate, keratan sulfate, and heparan sulfate), which are structural components of numerous tissues, including cartilage, bone, myelin, and basal lamina (40 ]) in the renal tubule lumen reduces Ca 2ϩ and Mg 2ϩ reabsorption (66). RENAL SULFATE CLEARANCEThe kidneys are the major avenue for SO 4 2Ϫ excretion in vertebrates. Nearly all of plasma SO 4 2Ϫ is ultrafilterable in mammals (4), whereas 80% and 47% of plasma SO 4 2Ϫ are ultrafilterable in birds (71) and fish (75), respectively. Variation in the estimates of the ultrafilterable fraction of plasma SO 4 2Ϫ in vertebrates may arise from species differences or variations in method of determination. Urine content is determined by glomerular filtration, tubular reabsorption, and tubular secretion. This review will focus on the latter and will provide only a brief overview of tubular reabsorption because it has been described in detail elsewhere (2,51,52,57).Reabsorption of filtered SO 4 2Ϫ occurs primarily in the proximal tubule (35) secretion does not occur in these animals. SO 4 2Ϫ loading apparently has no effect on the saturable reabsorptive transport maximum for SO 4 2Ϫ (Tm SO 4 2Ϫ ) in the renal tubule of the human, dog, and frog (3,28,48). In contrast, Tm SO 4 2Ϫ in rats is reduced ϳ50% after plasma SO 4 2Ϫ loading, indicating that adaptive mechanisms are in place to depress reabsorption, thus increasing excretion (27). Similarly, in domestic fowl, Tm SO 4 2Ϫ decreases with plasma SO 4 2Ϫ loading, leading to the conclusion that a fraction of the excreted SO 4 2Ϫ is the result of tubular secretion (30). Thiosulfate, an inhibitor of SO 4 2Ϫ transporters,

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“…Consequently, water replacement becomes of the highest importance to sustain body ionic regulation. Thus, marine teleosts are required to drink substantial amounts of seawater (Fuentes and Eddy, 1997), which once ingested undergoes an initial desalting step in the oesophagus by selective absorption of NaCl (Hirano and Mayer-Gostan, 1976;Parmelee and Renfro, 1983) to facilitate water absorption in the intestine.…”

Section: Introductionmentioning

confidence: 99%