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PubMed1978

Osmoregulation in the alga Vacuolaria virescens. Structure of the contractile vacuole and the nature of its association with the Golgi apparatus.

The contractile vacuole of the chloromonadophycean alga Vacuolaria virescens is a permanent structure that possesses a specialized membrane: subunits of this membrane have a diameter of 21-24 nm and in places are arranged in a regular hexagonal pattern. The lateral walls of these subunits form regularly spaced bristles or pegs which extend inwards from the trilaminar membrane for a distance of 13-15 nm. The contractile vacuole is situated immediately above an extensive Golgi apparatus that covers most of the anterior surface of the nucleus. Vesicles of Golgi origin give rise to subsidiary vacuoles which in turn empty into the contractile vacuole. Golgi vesicles, subsidiary vacuoles and the contractile vacuole contain similar electron-dense material. It is suggested that this material might be a highly hydrophilic substance which will attract water from the cytoplasm into the Golgi vesicles, subsidiary vacuoles and contractile vacuole from whence it is discharged from the cell. This method of osmoregulation is compared to that occurring in other algae and protozoa.

Chlorophyta↗
PubMed2003

Osmoregulation in an avian nectarivore, the whitebellied sunbird Nectarinia talatala: response to extremes of diet concentration.

Water intake of nectarivores is intrinsically linked to nectar concentration. Osmoregulation in whitebellied sunbirds Nectarinia talatala (body mass 9.3+/-0.1 g, mean +/- S.D., N=7), was examined by feeding them sucrose solutions, equivalent to extreme diet concentrations (0.07-2.5 mol l(-1) sucrose; 2-65% w/w), with and without supplementary drinking water. Total water gain was 33-515% of body mass daily. Cloacal fluid (CF) volume increased with diet dilution from 0.4% to 309% of body mass while increases in evaporative water loss (obtained by difference) were also recorded. Osmolality of CF demonstrated the largest scope yet recorded for a bird and was significantly correlated with water flux: mean values were 6-460 mosm kg(-1) H(2)O (minimum 3, maximum 1900 mosm kg(-1)). When supplementary water was provided, its consumption by birds fed concentrated diets (2.5 mol l(-1) sucrose) led to a dramatic reduction in CF osmolality, from 461+/-253 to 80+/-119 mosm kg(-1) fluid. Sunbirds maintained energy balance on sucrose diets varying tenfold in concentration, from 0.25 to 2.5 mol l(-1); however, on extremely dilute diets (0.07 and 0.1 mol l(-1) sucrose, lower than natural nectar concentrations) their inability to maintain energy balance was probably due to excess preformed water. Total osmotic excretion and concentrations of Na(+) and K(+) increased with high water fluxes, and are a possible physiological constraint for nectarivorous birds on artificial dilute diets devoid of electrolytes. Even low electrolyte levels in nectars may be adequate to replace these losses, but other physiological limitations to the intake of dilute nectars are increased energetic costs of solute recovery, increased heat loss and interference with digestive processes. Sunbirds therefore deal with sugar solutions spanning the range of nectar concentrations by shutting down water excretion on concentrated diets, or, on dilute diets, by producing extremely dilute CF with some of the lowest solute concentrations recorded.

Animal Nutritional Physiological Phenomena↗
PubMed2004

Cellular composition and ultrastructure of the gill epithelium of larval and adult lampreys: implications for osmoregulation in fresh and seawater.

Lampreys, one of the only two surviving groups of agnathan (jawless) vertebrates, contain several anadromous species that, during their life cycle, thus migrate from fresh to seawater and back to freshwater. Lampreys have independently evolved the same overall osmoregulatory mechanisms as the gnathostomatous (jawed) and distantly related teleost fishes. Lamprey gills thus likewise play a central role in taking up and secreting monovalent ions. However, the ultrastructural characteristics and distribution of their epithelial cell types [ammocoete mitochondria-rich (MR) cell, intercalated MR cell, chloride cell and pavement cell] differ in several respects from those of teleosts. The ultrastructural characteristics of these cells are distinctive and closely resemble those of certain ion-transporting epithelia in other vertebrates, for which the function has been determined. The data on each cell type, together with the stage in the life cycle at which it is found, i.e. whether in fresh or seawater, enable the following proposals to be made regarding the ways in which lampreys use their gill epithelial cells for osmoregulating in hypo- and hypertonic environments. In freshwater, the intercalated MR cell takes up Cl- and secretes H+, thereby facilitating the uptake of Na+ through pavement cells. In seawater, the chloride cell uses a secondarily active transcellular transport of Cl- to provide the driving force for the passive movement of Na+ through leaky paracellular pathways between these cells.

Animals↗
PubMed2006

Feeding and osmoregulation: dual function of the marine teleost intestine.

Experiments on Gulf toadfish Opsanus beta demonstrate how feeding impacts osmoregulation in the marine teleost intestine. A high Ca(2+) diet of pilchards Sardina pilchardus ([Ca(2+)]=404.2 mmol kg(-1)) was compared to a low Ca(2+) diet of common squid Loligo forbesi ([Ca(2+)]=1.3 mmol kg(-1)), as high [Ca(2+)] has been shown to stimulate intestinal anion exchange. Gastrointestinal fluids and blood plasma were collected over a time course from pre-feeding to 216 h post feeding. Following food intake, monovalent ions were largely absorbed across the intestinal epithelium, leaving a fluid rich in divalent ions, which have a lower osmotic coefficient and effectively reduce osmotic pressure in the lumen to allow for enhanced fluid absorption. Concentrations of Cl(-) and HCO (-)(3) in fluid along the gastrointestinal tract of fish fed both diets, particularly 1 and 2 days post-feeding, demonstrate that apical Cl(-)/HCO (-)(3) exchange plays a vital role in postprandial Cl(-) and water absorption. Postprandial acid-base balance disturbance as indicated by plasma alkalinization was limited or absent, indicating compensation for gastric acid secretion in this teleost fish. Plasma osmolality peaked 12 h post-feeding in toadfish fed squid, but was not accompanied by a significant increase in inorganic ion concentrations. Transient fluid secretion by the gastrointestinal tract was evident from reduced luminal Mg(2+) and SO (2-)(4) concentrations for 24-48 h post feeding. Discrepancy between the sum of inorganic osmolytes and measured osmotic pressure was attributed to organic osmolytes, which occurred at high concentrations in the stomach and anterior intestine for up to 24 h post feeding.

Animals↗
PubMed2006

Intestinal anion exchange in marine fish osmoregulation.

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 CO(2) with the resulting H(+) being extruded via a Na(+):H(+) exchange mechanism in the basolateral membrane. The basolateral H(+) extrusion is critical for the apical anion exchange and relies on the Na(+) gradient established by the Na(+)-K(+)-ATPase. This enzyme thereby ultimately fuels the secondary active transport of HCO(3)(-) and Cl(-) by the apical anion exchanger. High cellular HCO(3)(-) concentrations (>10 mmol l(-1)) are required for the anion exchange process and could be the result of both a high metabolic activity of the intestinal epithelium and a close association of the anion exchange protein and the enzyme carbonic anhydrase. The anion exchange activity in vivo is likely most pronounced in the anterior segment and results in net intestinal acid absorption. In contrast to other water absorbing vertebrate epithelia, the marine teleost intestine absorbs what appears to be a hypertonic fluid to displace diffusive fluid loss to the marine environment.

Animals↗
PubMed1983

Chloride cells and the hormonal control of teleost fish osmoregulation.

Teleost fish osmoregulation is largely the result of integrated transport activities of the gill, gut and renal system. The basic 'epithelial fabric' in each of these tissues is adapted to provide the appropriate transport mechanisms depending upon whether the fish is in fresh water or sea water. Net NaCl transport by the branchial epithelium reverses direction when euryhaline species migrate between the two media, providing a useful focus in experiments designed to elucidate mechanisms of differentiation and integration of transport function. Isolated opercular membranes and skins from certain seawater-adapted species are good models to study branchial salt extrusion mechanisms. These heterogeneous tissues generate short-circuit currents equal to net chloride secretion. The vibrating probe technique has allowed localization of all current and almost all conductance to the apical crypt of chloride cells. Area-specific surface current and conductance of chloride cells are 18 mA cm-2 and 580 mS cm-2 (1.7 omega cm2), ranking them as one of the most actively transporting and conductive cells known. There is no net sodium transport under short-circuit conditions but the chloride secretion process is sodium-dependent and ouabain and 'loop'-diuretic sensitive. Sodium fluxes through chloride cells are large (PNa = 5.2 X 10(-4) cms-1) nd appear passive and rate-limited by a single barrier. A link may exist between the active transport and leak pathways since sodium fluxes always account for 50% of chloride cell conductance. The sodium pathway is probably the chloride cell-accessory cell tight junction, although this is still unresolved. Chloride secretion can be rapidly modulated by several hormones, including catecholamines, somatostatin, glucagon, vasoactive intestinal polypeptide and urotensins I and II. Regulation by these hormones may be by rapid alterations of cellular cAMP levels. Differentiation of chloride cells and chloride secretion may be controlled by cortisol and prolactin. Cortisol stimulates chloride cell proliferation and differentiation and appears to interact with NaCl to initiate salt secretion. Prolactin appears to cause chloride cell dedifferentiation by reducing both the active-transport and leak pathways proportionately.(ABSTRACT TRUNCATED AT 400 WORDS)

Age Factors↗
PubMed2001

Osmoregulation in marine mammals.

Osmoregulation in marine mammals has been investigated for over a century; however, a review of recent advances in our understanding of water and electrolyte balance and of renal function in marine mammals is warranted. The following topics are discussed: (i) kidney structure and urine concentrating ability, (ii) sources of water, (iii) the effects of feeding, fasting and diving, (iv) the renal responses to infusions of varying salinity and (v) hormonal regulation. The kidneys of pinnipeds and cetaceans are reniculate in structure, unlike those of terrestrial mammals (except bears), but this difference does not confer any greater concentrating ability. Pinnipeds, cetaceans, manatees and sea otters can concentrate their urine above the concentration of sea water, but only pinnipeds and otters have been shown to produce urine concentrations of Na+ and Cl- that are similar to those in sea water. This could afford them the capacity to drink sea water and not lose fresh water. However, with few exceptions, drinking is not a common behavior in pinnipeds and cetaceans. Water balance is maintained in these animals via metabolic and dietary water, while incidental ingestion and dietary salt may help maintain electrolyte homeostasis. Unlike most other aquatic mammals, sea otters commonly drink sea water and manatees frequently drink fresh water. Among the various taxonomic groups of marine mammals, the sensitivity of the renin-angiotensin-aldosterone system appears to be influenced by the availability of Na+. The antidiuretic role of vasopressin remains inconclusive in marine mammals, while the natriuretic function of atrial natriuretic peptide has yet to be examined. Ideas on the direction of future studies are presented.

Animals↗
PubMed1997

Clarification of the promoter structure of the osmoregulated gpd1+ gene encoding an isozyme of NADH-dependent glycerol-3-phosphate dehydrogenase in fission yeast.

The gpd1+ gene of Schizosaccharomyces pombe, encoding an isozyme of NADH-dependent glycerol-3-phosphate dehydrogenase, is responsible for an osmoinducible glycerol production in response to external high osmotic stimuli, and its expression is osmoregulated at the level of transcription. In this study, the structure of the osmoinducible promoter of gpd1+ is described. Not only the core promoter elements including the putative TATA-box and transcription start site, but also a short upstream activation sequence (UAS) was identified, which are involved in the osmotic induction of the gpd1+ gene through the Wis1 MAP (mitogen activated protein) kinase pathway.

Base Sequence↗
PubMed1991

Chronic hypernatremia due to impaired osmoregulated thirst and vasopressin secretion.

We report the case of a young man who became adipsic following a subarachnoid hemorrhage and subsequently had two episodes of life-threatening hypernatremia. Investigations demonstrated that he had defective osmoregulated thirst and AVP release, but normal AVP responses to hypotension and nausea. There is also evidence that he had intact baroregulated thirst. We discuss the results of our investigations in the context of current models of hypothalamic-neurohypophysial function.

Adult↗
PubMed1989

Osmoregulation of vasopressin secretion in the insulin-withdrawn streptozotocin-treated diabetic rat.

To investigate whether hyperglycaemic ketoacidotic diabetic rats continue to osmoregulate the secretion of arginine vasopressin (AVP), male Wistar rats were injected with streptozotocin (150 mg/kg body weight). Rats rendered diabetic were maintained on protamine-zinc insulin (PZI) for 11 days (insulin-treated rats; n = 35), after which PZI was withdrawn for 72 h in half the rats (insulin-withdrawn rats). Insulin-withdrawn and -treated rats were divided into two groups; one was injected i.p. with distilled water (20 ml/kg) and the other with hypertonic saline (500 mmol NaCl/l; 20 ml/kg), and killed 30 min after injection. Insulin-withdrawn rats (water loaded and osmotically stimulated) were hyperglycaemic (16.5 +/- 0.8 and 16.5 +/- 0.9 mmol glucose/l respectively) and ketotic (2077 +/- 664 and 1474 +/- 170 mumol acetoacetate/l respectively). Insulin-treated rats were euglycaemic and non-ketotic. Osmotic manipulation caused similar changes in plasma sodium in both insulin-withdrawn and -treated rats. Plasma AVP was low in the water-loaded rats (0.6 +/- 0.1 and 4.5 +/- 0.9 pmol/l in the insulin-treated and -withdrawn rats respectively) and increased in rats injected with hypertonic saline (1.2 +/- 1.8 and 35.2 +/- 17.9 pmol/l respectively). There was no evidence of hypotension and hypovolaemia in any group of rats. Linear regression analysis defined the functions: plasma AVP = 2.56 (plasma Na-141), r = +0.63, P less than 0.01 for hyperglycaemic ketotic rats; plasma AVP = 0.83 (plasma Na-146), r = +0.78, P less than 0.001 for insulin-treated animals. The slopes and abscissal intercepts were significantly (P less than 0.05) different.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2001

Relative potency of three homologous natriuretic peptides (ANP, CNP and VNP) in eel osmoregulation.

Evidence has accumulated that atrial natriuretic peptide (ANP) plays important roles in sea-water adaptation in eels. However, the roles of the other two natriuretic peptides (CNP and VNP) in osmoregulation have not been examined yet. In the present study, the effects of homologous ANP, CNP and VNP were compared on plasma Na+ concentration (an indicator of plasma osmolality), hematocrit (an approximate indicator of blood volume) and drinking rate in freshwater- and seawater-adapted eels. In seawater eels, ANP and VNP, but not CNP, infused at 5 pmol/kg/min decreased plasma Na+ concentration and drinking rate and increased hematocrit. In freshwater eels, ANP and VNP failed to decrease plasma Na+ concentration but increased hematocrit to the same extent as in seawater eels. Inhibition of drinking was not detectable in freshwater eels because of little drinking before NP infusions. These results show that the effects of NPs on plasma Na+ concentration, drinking rate and hematocrit are mediated by NPR-A, since only ANP and VNP that bind with higher affinity to NPR-A are effective in seawater eels. The mechanisms of regulation of plasma Na+ concentration and hematocrit are unknown, but NPR-A is present in the responsible tissues for regulation of hematocrit in both freshwater and seawater eels. However, NPR-A may be absent in the tissues of freshwater eels that are responsible for regulation of plasma Na+ concentration.

Adaptation, Physiological↗
PubMed2005

Plasma and urine levels of electrolytes, urea and steroid hormones involved in osmoregulation of cetaceans.

Cetaceans are well adapted to their hyperosmotic environment by properly developed osmoregulatory ability. A question here is how they regulate water and mineral balances in marine habitats. In the present study, we determined blood and urine levels of various chemicals involved in osmoregulation, compared them with those in artiodactyls, and characterized the values in the whales. Blood and urine samples obtained from baleen whales of common minke (Balaenoptera acutorostrata), sei (B. borealis), and Bryde's whales (B. brydei), and toothed whales of sperm whales (Physeter macrocephalus) were analyzed for osmolality, major electrolytes, urea, steroid hormones and glucose. The urine osmolality and Na(+) concentrations in the cetaceans were much higher than those in the cattle. Furthermore, the cetaceans had 5 to 11-fold urea in plasma than the cattle, and 2 to 4-fold urea in urine. There were no significant difference in the plasma concentrations of corticosteroids between the cetaceans and the cattle. The present results indicate that the osmoregulatory parameters seem to be not affected by the reproductive stage and sex steroid hormones. The concentrations of urea in plasma and urine of the baleen whales were higher than those of the sperm whales, indicating a possibility that their osmoregulatory mechanisms may be correlated to their feeding habits. The present results suggest that cetaceans have unique osmoregulatory mechanisms by which they excrete strongly hypertonic urine to maintain fluid homeostasis in marine habitats.

Analysis of Variance↗
PubMed2004

Osmoadaptation and osmoregulation in archaea: update 2004.

The response of archaea to changes in external NaCl is reviewed and compared to what is known about osmoadaptation and osmoregulation in bacteria and eukaryotes. Cells placed in altered external NaCl exhibit short term and long term responses. The earliest events are likely to be water movement through aquaporin-like channels (efflux if external NaCl has been increased, influx into the cell if the external NaCl has been decreased) and ion movement (e.g., K+ moving in the direction opposite to water flow) through channels sensitive to osmotic pressure. A brief discussion of recent structures of homologues of these membrane proteins is presented. Accumulation of organic solutes, either by uptake from the medium or de novo synthesis, is triggered after these initial changes. Archaea have some unique organic solutes (osmolytes) that are not used by other organisms. These as well as other more common solutes have a role in stabilizing macromolecules from denaturation. Many osmolytes are distinguished by their stability in the cell and their lack of strong interactions with cellular components. A cell may respond by accumulating one or more temporary osmolytes, then over time readjust the intracellular solute distribution to what is optimal for cell growth under the new conditions. Coupled with the movement and accumulation of solutes is the induction of stress proteins (e.g., chaperonins) and, in some cases, transcriptional regulation of key enzymes. The response to NaCl stress of Methanococcus thermolithotrophicus is presented as an example of how one particular archaeon responds and adapts to altered osmotic pressure. The detailed response of many other archaea to osmotic stress will be needed in order to identify features (aside from some of the organic osmolytes) unique to the organisms in this kingdom.

Adaptation, Physiological↗
PubMed2000

Osmoadaptation and osmoregulation in archaea.

The response of archaea to changes in external NaCl is reviewed and compared to what is known about osmoadaptation and osmoregulation in bacteria and eukaryotes. Cells placed in altered external NaCl exhibit short term and long term responses. The earliest events are likely to be water movement through aquaporin-like channels (efflux if external NaCl has been increased, influx into the cell if the external NaCl has been decreased) and ion movement (e.g., K+ moving in the direction opposite to water flow) through channels sensitive to osmotic pressure. Accumulation of organic solutes, either by uptake from the medium or de novo synthesis, is triggered after these initial changes. Archaea have some unique organic solutes (osmolytes) that are not used by other organisms. These as well as other more common solutes have a role in stabilizing macromolecules from denaturation. Many osmolytes are distinguished by their stability in the cell and their lack of strong interactions with cellular components. A cell may respond by accumulating one or more temporary osmolytes, then over time readjust the intracellular solute distribution to what is optimal for cell growth under the new conditions. Coupled with the movement and accumulation of solutes is the induction of stress proteins (e.g., chaperonins) and, in some cases, transcriptional regulation of key enzymes. The response to NaCl stress of Methanococcus thermolithotrophicus is presented as an example of how one particular archaeon responds and adapts to altered osmotic pressure. Clearly, the detailed response of other archaea to osmotic stress will be needed in order to identify features (aside from some of the organic osmolytes) unique to the organisms in this kingdom.

Adaptation, Physiological↗
PubMed1995

Osmoregulation of neutral amino acid transport.

Neutral amino acids are important organic osmolytes found in most osmotically stressed cells. During prolonged hypertonic stress, accumulation of neutral amino acids contributes to the cell volume recovery and may protect cellular proteins against salt denaturation. Hypertonicity activates system A transport, a major neutral amino acid transporter in mammalian cells, by a microtubule-dependent mechanism. Similar to the regulation of amino acid efflux induced by hypotonic-swelling, influx via system A may be under the control of intracellular ionic strength. An osmotically sensitive repressor may negatively regulate the gene expression of a regulatory protein which activates the preexisting system A transporter protein. Hypertonically activated protein kinases may be involved in this osmoregulation of amino acid transport.

Amino Acids↗
PubMed2002

Effects of a parasite-induced nephritis on osmoregulation in the common carp Cyprinus carpio.

Carp Cyprinus carpio infected with the haemoflagellate Trypanoplasma borreli undergo progressive nephritis associated with a destruction of approx. 40% of the nephric tubules. In an attempt to analyse the effect of the nephritis on the osmoregulation of affected carp, the clinical chemical properties of plasma and urine samples were analysed. Parasitised carp excreted greater amounts of electrolytes in their urine than uninfected carp which excreted highly diluted urine with an osmolality of about 10% of plasma osmolality. During the course of the infection, urine osmolality increased up to 26% of plasma osmolality by Day 21 post-infection (p.i.). The plasma:urine ratio of Na+ also increased, while concomitant losses of Mg2+, Ca2+, K+ and inorganic phosphate were less pronounced. Infected carp were able to maintain a normal solute balance in their plasma. Plasma hydration (indicated by decreased protein contents) occurred on Day 21 p.i. Our data indicate that in T. borreli-infected carp, reabsorption processes of the distal renal tubule were disturbed, while secretory and absorption processes in the proximal tubule appeared to be less affected. In addition, infected carp were able to compensate their increased ion losses, probably by (energy-consuming) active absorption processes. The energy budget of infected carp was additionally affected by a substantial direct consumption of plasma glucose by the parasite.

Animals↗
PubMed1999

[The evolution of osmoregulation in vertebrates (on the centenary of the birth of E. M. Kreps)].

The paper substantiates the point of view that the first step in the evolution of osmoregulation in vertebrates involved development of water-impermeable epithelium which depended on specific distribution of aquaporins in plasma membranes, secretion of autacoids, formation of water-impermeable cell contacts with a high electrical resistance. Migration of vertebrates to the land was associated with appearance of the ability to regulate osmotic permeability of epithelium in a number of organs involving vasotocin and other pituitary hormones, insertion of aquaporins into the luminal plasma membrane. Enhancement of the renal role in the water-salt balance, intensification of the kidney function was due to a rise in renal circulation, glomerular filtration rate, and tubular reabsorption which, despite the increase in the energy expenditure, provided for an obvious enhancement of the renal work efficiency in maintaining the constancy of the internal medium. Colonisation of desert regions became possible in birds and mammals due to development of the system of urine osmotic concentration. Unlike the accepted point of view that this depended on the appearance of Henle's loops, the statement is substantiated that the leading role in this process is played by differentiation of the kidney into the cortex and medulla, as at our Laboratory nephron loops similar to Henle's loop have been revealed in the lamprey. In the vertebrates, the evolution shifted from the polyorgan to mono-organ type of osmotic homeostasis maintenance, with the leading role of the kidney in maintaining physico-chemical constants of the internal medium fluids.

Amino Acid Sequence↗
PubMed2001

Osmoregulation of vasopressin secretion via activation of neurohypophysial nerve terminals glycine receptors by glial taurine.

Osmotic regulation of supraoptic nucleus (SON) neuron activity depends in part on activation of neuronal glycine receptors (GlyRs), most probably by taurine released from adjacent astrocytes. In the neurohypophysis in which the axons of SON neurons terminate, taurine is also concentrated in and osmo-dependently released by pituicytes, the specialized glial cells ensheathing nerve terminals. We now show that taurine release from isolated neurohypophyses is enhanced by hypo-osmotic and decreased by hyper-osmotic stimulation. The high osmosensitivity is shown by the significant increase on only 3.3% reduction in osmolarity. Inhibition of taurine release by 5-nitro-2-(3-phenylpropylamino)benzoic acid, niflumic acid, and 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid suggests the involvement of volume-sensitive anion channels. On purified neurohypophysial nerve endings, activation of strychnine-sensitive GlyRs by taurine or glycine primarily inhibits the high K(+)-induced rise in [Ca(2+)](i) and subsequent release of vasopressin. Expression of GlyRs in vasopressin and oxytocin terminals is confirmed by immunohistochemistry. Their implication in the osmoregulation of neurohormone secretion was assessed on isolated whole neurohypophyses. A 6.6% hypo-osmotic stimulus reduces by half the depolarization-evoked vasopressin secretion, an inhibition totally prevented by strychnine. Most importantly, depletion of taurine by a taurine transport inhibitor also abolishes the osmo-dependent inhibition of vasopressin release. Therefore, in the neurohypophysis, an osmoregulatory system involving pituicytes, taurine, and GlyRs is operating to control Ca(2+) influx in and neurohormone release from nerve terminals. This elucidates the functional role of glial taurine in the neurohypophysis, reveals the expression of GlyRs on axon terminals, and further defines the role of glial cells in the regulation of neuroendocrine function.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗