Quercetin and NPPB-induced diminution of aldosterone action on Na+ absorption and ENaC expression in renal epithelium

In renal epithelial A6 cells, aldosterone applied for 24 h increased the transepithelial Cl- secretion over 30-fold due to activation of the Na+/K+/2Cl- cotransporter and stimulated the transepithelial Na+ absorption, activity of epithelial Na+ channel (ENaC), and alpha-ENaC mRNA expression. The stimulatory action of aldosterone on the transepithelial Na+ absorption, ENaC activity, and alpha-ENaC mRNA expression was diminished by 24h-pretreatment with quercetin (an activator of Na+/K+/2Cl- cotransporter participating in Cl- entry into the cytosolic space) or 5-nitro 2-(3-phenylpropylamino)benzoate (NPPB) (a blocker of Cl- channel participating in Cl- release from the cytosolic space), while 24h-pretreatment with bumetanide (a blocker of Na+/K+/2Cl- cotransporter) enhanced the stimulatory action of aldosterone on transepithelial Na+ absorption. On the other hand, under the basal (aldosterone-unstimulated) condition, quercetin, NPPB or bumetanide had no effect on transepithelial Na+ absorption, activity of ENaC or alpha-ENaC mRNA expression. These observations suggest that although aldosterone shows overall its stimulatory action on ENaC (transepithelial Na+ transport), aldosterone has an inhibitory action on ENaC (transepithelial Na+ transport) via activation of the Na+/K+/2Cl- cotransporter, and that modification of activity of Cl- transporter/channel participating in the transepithelial Cl- secretion influences the aldosterone-stimulated ENaC (transepithelial Na+ transport).     

Functional analysis of amino acids of the Na+/H+ exchanger that are important for proton translocation

The Na⁺/H⁺ exchanger is an integral membrane protein found in the plasma membrane of eukaryotic and prokaryotic cells. In eukaryotes it functions to exchange one proton for a sodium ion. In mammals it removes intracellular protons while in plants and fungal cells the plasma membrane form removes intracellular sodium in exchange for extracellular protons. In this study we used the Na⁺/H⁺ exchanger of Schizosaccharomyces pombe (Sod2) as a model system to study amino acids critical for activity of the protein. Twelve mutant forms of the Na⁺/H⁺ exchanger were examined for their ability to translocate protons as assessed by a cytosensor microphysiometer. Mutation of the amino acid Histidine 367 resulted in defective proton translocation. The acidic residues Asp145, Asp178, Asp266 and Asp267 were important in the proton translocation activity of the Na⁺/H⁺ exchanger. Mutation of amino acids His98, His233 and Asp241 did not significantly impair proton translocation by the Na⁺/H⁺ exchanger. These results confirm that polar amino acids are important in proton flux activity of Na⁺/H⁺ exchangers.     

Sodium-translocating adenosine triphosphatase inStreptococcus faecalis

Sodium-transloating ATPase in the fermentative bacteriumStreptococcus faecalis exchanges sodium for potassium ions. Sodium ions stimulate its activity, but K⁺ ions have no significant effect at present. Although the molecular nature of the sodium ATPase is not clear, the enzyme is distinct from other ion-motive ATPases (E₁E₂ type and F₁F₀ type) as judged by its resistance to vanadate as well as dicyclohexylcarbodiimde. The sodium ATPase is induced when cells are grown on media rich in sodium, particularly under conditions that limit the generation of a proton potential or block the constitutive sodium/proton antiporter, indicating that an increase in the cytoplasmic sodium level serves as the signal. The enzyme is not induced in response to K⁺ deprivation. The sodium ATPase may have evolved to cope with a sodium-rich environment under conditions that limit the magnitude of the proton potential.     

Sodium-dependent modulation of the renal Na−K-ATPase: Influence of mineralocorticoids on the cortical collecting duct

Summary Mineralocorticoids play a major role in the regulation of sodium transport in a variety of tissues, including the cortical collecting duct (CCD) of the mammalian nephron. To assess, in part, the underlying mechanism(s) of this control, the present studies were designed to evaluate, first, the influence of mineralocorticoids on the Na–K-ATPase activity in the rabbit CCD and, secondly, a possible role of sodium entry into the cell at the luminal border on the regulation of the Na–K-ATPase. In the first series of studies, rabbits were maintained on a low sodium diet which raised serum aldosterone levels from 16 to 70 ng/dl after 3–4 days, with further elevations being expressed with treatment for two weeks or more. In CCDs isolated from these animals, the Na–K-ATPase increased from 13 to 40 pmol ADP min^–1 mm^–1 after 3–4 days on the low sodium regimen, but then declined, returning to control values after approximately 2 weeks. This decline in activity was preceded by a decrease in the Na⁺ concentration of the urine to low levels and hence, likely coincided with a decreased delivery of sodium to, and sodium entry into the cells of, the CCD. If dietary manipulations were used to maintain a high delivery of sodium to the CCD in the animal, elevation of plasma mineralocorticoid levels by treatment with deoxycorticosterone acetate (DOCA) caused a similar elevation in the Na–K-ATPase activity after 3–4 days, which did not decline with continued treatment for up to 2 weeks. Furthermore, it was observed that mineralocorticoids only exerted their effect on the Na–K-ATPase after a latent period of 1 day, well after sodium excretion had fallen, indicating that sodium entry into the CCD cells was already stimulated. If animals were simultaneously treated with DOCA and the sodium channel blocker amiloride for 3–4 days, the effects on the Na–K-ATPase were markedly reduced, whereas amiloride treatment alone had no effect on the enzyme activity. Since others have shown that mineralocorticoids induce synthesis of the Na–K-ATPase subunits in toad bladder cells in an amiloride-insensitive manner, sodium must be exerting its effect on a process after translation. It is concluded that the initial effect of mineralocorticoids in the CCD is on sodium entry with a delayed induction of the Na–K-ATPase, which is regulated by Na-dependent modulation of a posttranslational process.     

Genetic mosaic analysis reveals that GATA-4 is required for proper differentiation of mouse gastric epithelium.

During mouse embryogenesis GATA-4 is expressed first in primitive endoderm and then in definitive endoderm derivatives, including glandular stomach and intestine. To explore the role of GATA-4 in specification of definitive gastric endoderm, we generated chimeric mice by introducing Gata4(-/-) ES cells into ROSA26 morulae or blastocysts. In E14.5 chimeras, Gata4(-/-) cells were represented in endoderm lining the proximal and distal stomach. These cells expressed early cytodifferentiation markers, including GATA-6 and ApoJ. However, by E18.5, only rare patches of Gata4(-/-) epithelium were evident in the distal stomach. This heterotypic epithelium had a squamous morphology and did not express markers associated with differentiation of gastric epithelial cell lineages. Sonic Hedgehog, an endoderm-derived signaling molecule normally down-regulated in the distal stomach, was overexpressed in Gata4(-/-) cells. We conclude that GATA-4-deficient cells have an intrinsic defect in their ability to differentiate. Similarities in the phenotypes of Gata4(-/-) chimeras and mice with other genetically engineered mutations that affect gut development suggest that GATA-4 may be involved in the gastric epithelial response to members of the TGF-beta superfamily.     

Electron and proton transport across the plasma membrane

Transplasma membrane electron transport in both plant and animal cells activates proton release. The nature and components of the electron transport system and the mechanism by which proton release is activated remains to be discovered. Reduced pyridine nucleotides are substrates for the plasma membrane dehydrogenases. Both plant and animal membranes have unusual cyanide-insensitive oxidases so oxygen can be the natural electron acceptor. Natural ferric chelates or ferric transferrin can also act as electron acceptors. Artificial, impermeable oxidants such as ferricyanide are used to probe the activity. Since plasma membranes containb cytochromes, flavin, iron, and quinones, components for electron transport are present but their participation, except for quinone, has not been demonstrated. Stimulation of electron transport with impermeable oxidants and hormones activates proton release from cells. In plants the electron transport and proton release is stimulated by red or blue light. Inhibitors of electron transport, such as certain antitumor drugs, inhibit proton release. With animal cells the high ratio of protons released to electrons transferred, stimulation of proton release by sodium ions, and inhibition by amilorides indicates that electron transport activates the Na⁺/H⁺ antiport. In plants part of the proton release can be achieved by activation of the H⁺ ATPase. A contribution to proton transfer by protonated electron carriers in the membrane has not been eliminated. In some cells transmembrane electron transport has been shown to cause cytoplasmic pH changes or to stimulate protein kinases which may be the basis for activation of proton channels in the membrane. The redox-induced proton release causes internal and external pH changes which can be related to stimulation of animal and plant cell growth by external, impermeable oxidants or by oxygen.     

Increased platelet sodium-proton exchange rates in insulin-dependent (type 1) diabetic patients with nephropathy and hypertension

In order to assess the potential role of the plasma membrane sodium-proton (Na^–/H⁺) exchanger in the pathogenesis of diabetic nephropathy, we investigated 32 insulin dependent (type 1) diabetic patients and 21 control subjects. We tested the Na⁺/H⁺ exchange as the rate of amiloride sensitive and sodium dependent volume gain of platelets suspended in sodium propionate. Patients with diabetic nephropathy had significantly increased rates of Na⁺/H⁺ exchange (0.31 ± 0.06 s^–1 × 10–2) when compared to those without nephropathy (0.24 ± 0.07, p < 0.05) or to a control group (0.23 ± 05, p < 0.05). Nine patients who were classified as hypertensive had a highly significant increase in the Na⁺/H⁺ exchange rates when compared to 23 non-hypertensive diabetic patients: 0.33 ± 0.04 versus 0.24 ± 0.06 (p < 0.001). There was no significant correlation between the Na⁺/H⁺ exchange rates and age, diabetes duration, glycated hemoglobin or fructosamine levels on the day of the test. In summary, the data presented here demonstrate an increase in the Na⁺/H⁺ exchange rate in insulin-dependent diabetic patients with nephropathy and hypertension     

Mucosal acidification and an acid microclimate in the hen colon in vitro

Experiments were performed on isolated, stripped colonic epithelia of low-salt-adapted hens (Gallus domesticus) in order to characterize acid secretion by this tissue. With symmetric, weak buffer solutions, colonic epithelia acidified both mucosal and serosal sides. Titration measurements of the mucosal acidification rate (pH-stat technique) averaged 1.63±0.25 Eq·cm^-2·h^-1. Mucosal acidification was also evident in colons from high-salt-adapted birds and in low-salt-adapted coprodeum, but was completely abolished in the high-salt coprodeum. Mucosal acidification by low-salt-adapted colonic epithelium was unaffected by sodium replacement, mucosal amiloride (10^-3 mol·l^-1), and serosal ouabain (5x10^-4 mol·l^-1), although all three treatments significantly reduced or reversed the short-circuit current. Acetazolamide (10^-3 mol·l^-1, serosal) reduced mucosal acidification by 15% and simultaneously increased short-circuit current by a similar amount. Colonic epithelia incubated in glucose-free solutions had significantly lower acidification rates (0.59±0.13 Eq·cm^-2·h^-1, P<0.002 versus controls) and addition of glucose (15 mmol·l^-1), but not galactose, partially restored acidification to control levels. Anoxia (N₂ gassing) completely inhibited short-circuit current, but reduced acidification by only 30%. A surface microclimate pH, nearly 2 pH units more acidic than the bath pH of 7.1–7.4 was measured in low-salt-adapted colon and coprodeum. The acid microclimate of both tissues was partially attenuated by adaptation to a high-salt diet. Colonic microclimate pH was dependent on the presence of glucose and sensitive to the bath pH. Histochemical staining for carbonic anhydrase localized this enzyme to cytoplasm and lateral margins of one subfraction of colonic cells, and to cytoplasm in a second subpopulation Intense staining was also evident in subepithelial capillaries. These results suggest that a large part of mucosal acidification and maintenance of the acid microclimate in hen colon may be dependent on glycolysis and metabolic acid production, although a smaller, electrogenic and acetazolamidesensitive component also appears to exist. This latter component may become more prominent under conditions of cellular acidification.Abbreviations CA carbonic anhydrase - I _SC short circuit current - NFM N-ethylmaleimide - PD transepithelial potential - SCFA short chain fatty acids     

Capsaicin inhibits intestinal Cl- secretion and promotes Na+ absorption by blocking TRPV4 channels in healthy and colitic mice

Although capsaicin has been studied extensively as an activator of the transient receptor potential vanilloid cation channel subtype 1 (TRPV1) channels in sensory neurons, little is known about its TRPV1-independent actions in gastrointestinal health and disease. Here, we aimed to investigate the pharmacological actions of capsaicin as a food additive and medication on intestinal ion transporters in mouse models of ulcerative colitis (UC). The short-circuit current (I_sc) of the intestine from WT, TRPV1-, and TRPV4-KO mice were measured in Ussing chambers, and Ca²⁺ imaging was performed on small intestinal epithelial cells. We also performed Western blots, immunohistochemistry, and immunofluorescence on intestinal epithelial cells and on intestinal tissues following UC induction with dextran sodium sulfate. We found that capsaicin did not affect basal intestinal I_sc but significantly inhibited carbachol- and caffeine-induced intestinal I_sc in WT mice. Capsaicin similarly inhibited the intestinal I_sc in TRPV1 KO mice, but this inhibition was absent in TRPV4 KO mice. We also determined that Ca²⁺ influx via TRPV4 was required for cholinergic signaling–mediated intestinal anion secretion, which was inhibited by capsaicin. Moreover, the glucose-induced jejunal I_scvia Na⁺/glucose cotransporter was suppressed by TRPV4 activation, which could be relieved by capsaicin. Capsaicin also stimulated ouabain- and amiloride-sensitive colonic I_sc. Finally, we found that dietary capsaicin ameliorated the UC phenotype, suppressed hyperaction of TRPV4 channels, and rescued the reduced ouabain- and amiloride-sensitive I_sc. We therefore conclude that capsaicin inhibits intestinal Cl^- secretion and promotes Na⁺ absorption predominantly by blocking TRPV4 channels to exert its beneficial anti-colitic action.     

Morphological adaptations to induced changes in transepithelial sodium transport in chicken lower intestine (coprodeum): a study of resalination, aldosterone stimulation, and epithelial turnover

Transepithelial sodium transport and epithelial morphology during short-term adaptation to resalination or aldosterone stimulation were studied in the chicken coprodeum. Coprodeum was sampled for light and electron microscopy after 0–3 days of resalination in hens on a low-NaCl diet and after 0–6 days of aldosterone stimulation in hens on a high-NaCl diet. Sodium transport was measured in vitro with Ussing chambers. Plasma osmolality and electrolyte concentrations were measured in aldosterone-stimulated hens. Epithelial proliferation and migration between 1 h and 16 days were investigated in chickens on high-NaCl and low-NaCl diets using a bromodeoxyuridine technique. Resalination abolished the otherwise high sodium transport within 1 day, while the height and number of microvilli, as well as the number of brush cells, decreased over 3 days. Aldosterone stimulation increased sodium transport, the height and number of microvilli, and the brush-cell number. Bromodeoxyuridine studies indicated an epithelial cell turnover of more than 16 days. The results thus demonstrate that epithelial cells have an unusual capacity to adjust rap- idly to variations in sodium intake. A strong correlation between structure and function was apparent.     

Immunocytochemical characterization of two types of microvillar cells in rodent olfactory epithelium

Microvillar cells (MCs) have been identified in the olfactory epithelium of various mammalian species from rodents to humans. Studies on properties and functions of MCs to date have yielded partially controversial results, supporting alternatively an epithelial or a neuronal nature of these cells. In the present study, single and double immunolabeling investigations were carried out using antibodies against cytoskeletal and integral membrane proteins in order to further characterize MCs in rat and mouse olfactory epithelium. Application of antibodies against ankyrin (ANK), a protein that links integral membrane proteins to the submembrane cytoskeleton, led to intense labeling of the basolateral membranes of numerous cells with characteristic MC morphology. ANK-immunoreactive (ir) cells bore an apical tuft of -actin-ir microvilli, were filled with cytokeratin 18 (CK18)-ir filamentous network, and extended a basal process that appeared to end above the basal membrane. Immunoreactions for villin, an actin-crosslinking protein particularly prominently expressed in brush cells in the gastrointestinal and respiratory tract epithelia, and for the -subunit of sodium-potassium ATPase (Na⁺, K⁺-ATPase), revealed that ANK-ir MCs fall into two subpopulations. The less frequent type I MCs displayed villin immunoreactivity in their apical microvilli and underneath the basolateral membranes; the more numerous type II MCs were negative for villin but possessed intense basolateral immunoreactivity for Na⁺, K⁺-ATPase. Strong reactivity for the epithelial-type integral membrane protein of adherens junctions, E-Cadherin, was localized in basolateral membranes of both types of MCs. Our results support an epithelial nature of ANK-ir MCs in rat and mouse olfactory epithelium. Type I MCs strongly resemble brush cells in their immunocytochemical characteristics, namely, their ANK reactivity, CK18 reactivity, and villin reactivity. The intense Na⁺, K⁺-ATPase reactivity of type II MCs implicates these cells in transport processes.     

Control of Na+ and H+ transports by exocytosis/endocytosis phenomena in a tight epithelium

The relationship linking Na⁺ and H⁺ transports and exocytosis/endocytosis located in the apical membranes of the frog skin epithelium was investigated under various conditions of ion transport stimulation. The exocytosis process, indicating insertion of intracellular vesicles, which were preloaded with fluorescent FITC-dextran (FD), was measured by following the FD efflux in the apical bathing solution.Na⁺ transport stimulators such as serosal hypotonic shock (replacement of serosal Ringer solution by half-Ringer or 4/5-Ringer), apical PCMPS (10^–3 m) and amphotericin-B (20 g/ml), were also found to stimulate the exocytotic rates of FD. Acidification of the epithelium by CO₂ or post NH₄ load, conditions which increase the proton secretion also stimulated the FD release in the apical bathing solution. On the other hand, alkalization of the epithelial cells increased the endocytosis rate. Hypotonic shock, acid load and PCMPS induced an increase in cell calcium which is probably the signal within the cell for exocytosis. In addition, quantitative spectrofluorimetric measurements of F-actin content after rhodamine-phalloidin staining, indicated a decrease in the F-actin content as a result of cell acidosis, hypotonic conditions and amphotericin additions. It is proposed that the insertion/retrieval of intracytoplasmic vesicles containing H⁺ pumps plays a key role in the regulation of proton secretion in tight epithelia. In addition, it is suggested that cytoskeleton depolymerization of F-actin filaments facilitates H⁺ pump insertion. A comparable working hypothesis for the control of Na⁺ transport is proposed.This work was supported by grants from the Commissariat à l'Energie Atomique and The Centre National de la Recherche Scientifique UA 638.We would like to thank Dr. R.M. Hays and Dr. J. Condeelis (Albert Einstein College of Medicine, New York) for stimulating discussions. The confocal microscope observations were done through the courtesy of Dr. C. Sardet and C. Rouvière (Station Marine de Villefranche/mer France).     

Mechanisms of liquid flux across pulmonary alveolar epithelial cell monolayers

Summary Active transport of sodium by pulmonary alveolar epithelial cells (AEC) is believed to be an important component of edema clearance in the normal and injured lung. Data supporting this premise have come from measurements of sodium movement across AEC monolayers or from perfused lung model systems. However, direct measurement of fluid flux across AEC monolayers has not been reported. In the present work, AEC were studied with an experimental system for the measurement of fluid flux (Jv) across functionally intact cell monolayers. Primary adult rat type II alveolar epithelial cells were cultured on 0.8 μm nuleopore filters previously coated with gelatin and fibronectin. Intact monolayers were verified by high electrical resistance (> 1000 Θ) at 4–5 d of primary culture. At the same time interval, transmission electron microscopy revealed cells with type I cell-like morphology throughout the monolayer. These were characterized by both adherens and tight junctional attachments. Fluid flux across the monolayers was measured volumetrically over a period of 2 h in the presence of HEPES-buffered DMEM containing 3% fatty acid-free bovine serum albumin. Flux (Jv) was inhibited 39% by 1 × 10⁻⁴ M ouabain (P < 0.01) and 27% by 5 × 10⁻⁴ M amiloride (P < 0.05). These data support the concept that AEC Na⁺/K⁺-ATPase and Na⁺ transport systems are important determinants of AEC transepithelial fluid movement in vitro.     

Yarrowia lipolytica possesses two plasma membrane alkali metal cation/H+ antiporters with different functions in cell physiology

The family of Nha antiporters mediating the efflux of alkali metal cations in exchange for protons across the plasma membrane is conserved in all yeast species. Yarrowia lipolytica is a dimorphic yeast, phylogenetically very distant from the model yeast Saccharomyces cerevisiae. A search in its sequenced genome revealed two genes (designated as YlNHA1 and YlNHA2) with homology to the S. cerevisiae NHA1 gene, which encodes a plasma membrane alkali metal cation/H+ antiporter. Upon heterologous expression of both YlNHA genes in S. cerevisiae, we showed that Y. lipolytica antiporters differ not only in length and sequence, but also in their affinity for individual substrates. While the YlNha1 protein mainly increased cell tolerance to potassium, YlNha2p displayed a remarkable transport capacity for sodium. Thus, Y. lipolytica is the first example of a yeast species with two plasma membrane alkali metal cation/H+ antiporters differing in their putative functions in cell physiology; cell detoxification vs. the maintenance of stable intracellular pH, potassium content and cell volume.     

A low-salt diet facilitates Cl secretion in hen lower intestine

Summary The regulation of sodium and chloride transport in hen coprodeum by mineralocorticoids was investigated with isolated epithelia under short-circuit conditions. Unidirectional fluxes of Na and Cl were measured by isotopes and modulated by amiloride, theophylline and bumetanide. Hens were maintained either on low-NaCl diet (LS) or on high-NaCl diet (HS). Plasma aldosterone (PA) levels of these groups were measured with radioimmunoassay. A group of HS hens received injections of aldosterone on a 6-hr schedule before experiments. Another group of LS hens was resalinated, and experiments carried out on a 24-hr interval.Salt deprivation stimulated PA levels ninefold, compared to HS hens. Na absorption was stimulated according to previous reports. Electrogenic Cl secretion was elicited by theophylline and partially inhibited by bumetanide. Modulation of PA levels by diet, resalination or aldosterone injection changed the magnitude of electrogenic Cl secretion in parallel between 0.5 eq/cmau2 · hr (HS) and 4 eq/cm² · hr (LS), with pronounced alteration in tissue resistance.The results demonstrate a new action of aldosterone which besides stimulating Na absorption also directly or indirectly elicits Cl secretion. Evidence is presented for a hormonal adaptation of chloride transport in this epithelium. There was a morphological change of the apical plasma membrane and further experiments will have to clarify the exact cellular nature of this process.     

Functional characterization of a wheat plasma membrane Na+/H+ antiporter in yeast

The functional analysis of the sodium exchanger SOS1 from wheat, TaSOS1, was undertaken using Saccharomyces cerevisiae as a heterologous expression system. The TaSOS1 protein, with significant sequence homology to SOS1 sodium exchangers from Arabidopsis and rice, is abundant in roots and leaves, and is induced by salt treatment. TaSOS1 suppressed the salt sensitivity of a yeast strain lacking the major Na⁺ efflux systems by decreasing the cellular Na⁺ content while increasing K⁺ content. Na⁺/H⁺ exchange activity of purified plasma membrane from yeast cells expressing TaSOS1 was higher than controls transformed with empty vector. These results demonstrate that TaSOS1 contributes to plasma membrane Na⁺/H⁺ exchange.     

Characterization of the ion transport activity of the budding yeast Na/H antiporter, Nha1p, using isolated secretory vesicles

The Saccharomyces cerevisiae Nha1p, a plasma membrane protein belonging to the monovalent cation/proton antiporter family, plays a key role in the salt tolerance and pH regulation of cells. We examined the molecular function of Nha1p by using secretory vesicles isolated from a temperature sensitive secretory mutant, sec4-2, in vitro. The isolated secretory vesicles contained newly synthesized Nha1p en route to the plasma membrane and showed antiporter activity exchanging H⁺ for monovalent alkali metal cations. An amino acid substitution in Nha1p (D266N, Asp-266 to Asn) almost completely abolished the Na⁺/H⁺ but not K⁺/H⁺ antiport activity, confirming the validity of this assay system as well as the functional importance of Asp-266, especially for selectivity of substrate cations. Nha1p catalyzes transport of Na⁺ and K⁺ with similar affinity (12.7 mM and 12.4 mM), and with lower affinity for Rb⁺ and Li⁺. Nha1p activity is associated with a net charge movement across the membrane, transporting more protons per single sodium ion (i.e., electrogenic). This feature is similar to the bacterial Na⁺/H⁺ antiporters, whereas other known eukaryotic Na⁺/H⁺ antiporters are electroneutral. The ion selectivity and the stoichiometry suggest a unique physiological role of Nha1p which is distinct from that of other known Na⁺/H⁺ antiporters.     

Ultrahistochemical and autoradiographic evidence for epithelial transport in the uterus of the ovoviviparous salamander,Salamandra salamandra (L.) (Amphibia,Urodela)

Summary The uterine epithelium of pregnant females of the terrestrial ovoviviparous Salamandra salamandra is characterized by a considerable enlargement of its basolateral surface. Chloride and cations (among others sodium), preferentially within the intercellular spaces, can be demonstrated ultrahistochemically. There is indirect evidence of Na⁺-K⁺-ATPase activity along the basolateral plasma membranes of the epithelial cells using the Sr-technique for demonstration of a K⁺-NPPase and ³H-ouabain autoradiography. Preliminary measurements reveal a potential difference across the uterine wall of 15–25mV, the lumenal (mucosal) surface being negative with respect to the coelomic (serosal) surface, and a short circuit current of 200–300 A. The possibly electrogenic ion transport is ouabain-sensitive. The results are in agreement with the model of a forward transporting, i.e. absorptive epithelium. An active transport of solute out of the uterine lumen across the epithelium to the subjacent connective tissue and the blood vessels may be involved in the regulation of an intrauterine milieu appropriate for the development of the offspring.I am indebted to Miss Dr. U. Beigel, Zoologisches Institut der Universität Münster, for linguistic help