Isosmotic Saline Research Articles

Growth and Physiological Response of Litopenaeus stylirostris Acclimated to Low Salinity

AbstractJuveniles of wild Pacific blue shrimp Litopenaeus stylirostris (mean initial weight ± standard deviation = 1.5 ± 0.1 g) were acclimated from a natural seawater salinity of 35‰ to salinities of 0, 2.5, 5.0, 7.5, 10, 15, and 25‰. After reaching the desired salinities, L. stylirostris were cultured for 32 d and growth, feed conversion ratio, and survival, as well as hemolymph and culture water osmolality, were determined. The L. stylirostris exposed to 0‰ died before or shortly after reaching the salinity end point. Final mean body weight of L. stylirostris held at 2.5‰ (3.1 ± 0.8 g) was significantly reduced compared with all other treatments. In contrast, those held at salinities from 5‰ to 35‰ had similar performance, with mean body final weight ranging from 3.8 to 4.5 g, showing that L. stylirostris can be cultured across this range of salinities without adversely affecting growth, survival, or feed conversion ratio. Litopenaeus stylirostris is a euryhaline organism, able to maintain its hemolymph osmolality relatively constant despite changes in salinity. The isosmotic salinity of L. stylirostris, estimated from the point of intersection between the regression lines of water salinity versus water osmolality and water salinity versus hemolymph osmolality, was 26.7‰. Litopenaeus stylirostris is an efficient osmoregulator with potential for low‐salinity culture.

Enhanced β-carotene and Biomass Production by Induced Mixotrophy in Dunaliella salina across a Combined Strategy of Glycerol, Salinity, and Light.

Current mixotrophic culture systems for Dunaliella salina have technical limitations to achieve high growth and productivity. The purpose of this study was to optimize the mixotrophic conditions imposed by glycerol, light, and salinity that lead to the highest biomass and β-carotene yields in D. salina. The combination of 12.5 mM glycerol, 3.0 M salinity, and 50 μmol photons m−2 s−1 light intensity enabled significant assimilation of glycerol by D. salina and consequently enhanced growth (2.1 × 106 cell mL−1) and β-carotene accumulation (4.43 pg cell−1). The saline and light shock induced the assimilation of glycerol by this microalga. At last stage of growth, the increase in light intensity (300 μmol photons m−2 s−1) caused the β-carotene to reach values higher than 30 pg cell−1 and tripled the β-carotene values obtained from photoautotrophic cultures using the same light intensity. Increasing the salt concentration from 1.5 to 3.0 M NaCl (non-isosmotic salinity) produced higher growth and microalgal β-carotene than the isosmotic salinity 3.0 M NaCl. The mixotrophic strategy developed in this work is evidenced in the metabolic capability of D. salina to use both photosynthesis and organic carbon, viz., glycerol that leads to higher biomass and β-carotene productivity than that of an either phototrophic or heterotrophic process alone. The findings provide insights into the key role of exogenous glycerol with a strategic combination of salinity and light, which evidenced unknown roles of this polyol other than that in osmoregulation, mainly on the growth, pigment accumulation, and carotenogenesis of D. salina.

Ageing attenuates the effect of extracellular hyperosmolality on whole-body heat exchange during exercise-heat stress.

In humans, hypohydration attenuates sweat secretion and attenuates whole-body heat loss, probably to mitigate further fluid losses and thereby support blood pressure regulation. Recently, however, we demonstrated that the hypohydration-mediated reduction in net whole-body heat exchange (evaporative heat loss-dry heat gain) was blunted in middle-aged compared to younger men during moderate exercise in dry heat; albeit, the underpinning mechanisms could not be determined. Here we evaluated the hypothesis that those findings stemmed from a diminished influence of extracellular hyperosmolality on net whole-body heat exchange in middle-aged-to-older compared to young men. Consistent with that hypothesis, extracellular hyperosmolality induced by an intravenous infusion of hypertonic saline (3% NaCl) reduced net heat exchange and augmented rectal temperature to a greater extent in the young compared to middle-aged-to-older men. Thus, age-related differences in the influence of hypohydration on thermoregulatory function appear to be due to blunted sensitivity to hyperosmolality with ageing. We recently demonstrated that sweating-induced hypohydration attenuated whole-body heat dissipation to a greater extent in young compared to middle-aged men during exercise-heat stress. Here, we evaluated whether this divergent response stemmed from an attenuated influence of extracellular hyperosmolality on heat exchange with ageing. To achieve this, ten young (mean(SD): 25(5)years) and ten middle-aged-to-older (61(5)years) men completed two trials involving a 90-min intravenous infusion of isosmotic saline (0.9% NaCl; ISO) or hyperosmotic saline (3.0% NaCl; HYP) followed by 60min of cycling at a fixed metabolic heat production of 250W/m2 (∼50% peak aerobic power) in dry heat (40°C, ∼17% relative humidity). Whole-body net heat exchange (evaporative heat loss-dry heat gain) was measured via direct calorimetry. Rectal temperature was monitored continuously. Heat exchange was attenuated in HYP compared to ISO in the young (233(20) vs. 251(17)W/m2 ; P=0.002) but not older group (229(16) vs. 227(20)W/m2 ; P=0.621). Further, heat exchange was lower in the middle-aged-to-older vs. young men in ISO (P=0.034) but not in HYP (P=0.623). Similarly, end-exercise rectal temperature was greater in HYP relative to ISO in the young (38.3(0.4)°C vs. 37.9(0.3)°C; P=0.015) but not the middle-aged-to-older men (38.3(0.3)°C vs. 38.2(0.2)°C; P=0.652). Compared to the young, rectal temperature was greater in the middle-aged-to-older during ISO (P=0.035) whereas no between-group difference was observed in HYP (P=0.746). Our findings indicate that ageing blunts the effect of extracellular hyperosmolality on thermoregulatory function during exercise-heat stress.

Ionoregulatory aspects of the hypoxia-induced osmorespiratory compromise in the euryhaline Atlantic killifish (Fundulus heteroclitus): the effects of salinity.

The osmorespiratory compromise is a physiological trade-off between the characteristics of the gill that promote respiratory gas exchange and those that limit passive flux of ions and water with the environment. In hypoxia, changes in gill blood flow patterns and functional surface area that increase gas transfer can promote an exacerbation in ion and water flux. Our goal was to determine whether the osmorespiratory compromise is flexible, depending on environmental salinity (fresh, isosmotic and sea water) and oxygen levels (hypoxia) in euryhaline killifish, Fundulus heteroclitus Plasma ion concentrations were minimally affected by hypoxia, indicating a maintenance of osmoregulatory homeostasis. In freshwater killifish, hypoxia exposure reduced branchial Na+/K+-ATPase and NEM-sensitive ATPase activities, as well as diffusive water flux rates. Unidirectional Na+ influx and Na+ efflux decreased during hypoxia in freshwater, but net Na+ flux remained unchanged. Net loss rates of Cl-, K+ and ammonia were also attenuated in hypoxia, suggesting both transcellular and paracellular reductions in permeability. These reductions appeared to be regulated phenomena as fluxes were restored immediately in normoxia. Na+ flux rates increased during hypoxia in 11 ppt, but decreased in 35 ppt, the latter suggesting a similar response to hypoxia to that in freshwater. In summary, freshwater and seawater killifish experience a reduction in gill permeability, as seen in other hypoxia-tolerant species. Fish acclimated to isosmotic salinity increased Na+ influx and efflux rates, as well as paracellular permeability in hypoxia, responses in accord with the predictions of the classic osmorespiratory compromise.

The osmorespiratory compromise: physiological responses and tolerance to hypoxia are affected by salinity acclimation in the euryhaline Atlantic killifish (Fundulus heteroclitus).

The characteristics of the fish gill that maximize gas exchange are the same that promote diffusion of ions and water to and from the environment; therefore, physiological trade-offs are likely to occur. Here, we investigated how salinity acclimation affects whole-animal respiratory gas exchange during hypoxia using Fundulus heteroclitus, a fish that inhabits salt marshes where salinity and oxygen levels vary greatly. Salinity had marked effects on hypoxia tolerance, with fish acclimated to 11 and 35ppt showing much longer time to loss of equilibrium (LOE) in hypoxia than 0ppt-acclimated fish. Fish acclimated to 11ppt (isosmotic salinity) exhibited the greatest capacity to regulate oxygen consumption rate (ṀO2 ) under hypoxia, as measured through the regulation index (RI) and Pcrit At 35ppt, fish had a higher routine metabolic rate (RMR) but a lower RI than fish at 11ppt, but there were no differences in gill morphology, ventilation or blood O2 transport properties between these groups. In contrast, 0ppt-acclimated fish had the highest ventilation and lowest O2 extraction efficiency in normoxia and hypoxia, indicating a higher ventilatory workload in order to maintain similar levels of ṀO2 These differences were related to alterations in gill morphology, where 0ppt-acclimated fish had the smallest lamellar surface area with the greatest epithelial cell coverage (i.e. thicker lamellae, longer diffusion distance) and a larger interlamellar cell mass, contrasting with 11ppt-acclimated fish, which had overall the highest respiratory surface area. The alteration of an array of physiological parameters provides evidence for a compromise between salinity and hypoxia tolerance in killifish acclimated to freshwater.

Effect of low salinity on acute arsenic toxicity and bioconcentration in shrimp Litopenaeus vannamei juveniles

This study investigated acute arsenic toxicity and bioconcentration capacity in Litopenaeus vannamei because it has been frequently exposed to lower salinities than its isosmotic point (25 g L−1). Juveniles (9.9 ± 0.4 g) were exposed to low (5–10 g L−1) and isosmotic salinity (25 g L−1) levels; As values were 30.8, 20.2, 16.8 and 13.9 mg L−1 at 5 g L−1; 30.4, 19.1, 16.8 and 14.8 mg L−1 at 10 g L−1; 31.5, 19.0, 15.0 and 11.9 mg L−1 at 25 g L−1 at 24, 48, 72 and 96 h LC50, respectively. No significant differences were found among As LC50 values calculated for different salinity levels and same exposure times, concluding that low salinity did not affect shrimp sensitivity to As. Likewise, no significant differences were observed in As bioconcentration in shrimp exposed to the same waterborne As and distinct salinity, supporting the results of acute toxicity. Bioconcentration factors of As maintained a relatively stable tendency where all values (0.8 ± 0.2 to 1.7 ± 0.4) were statistically comparable to 1, indicating that As was accumulated in a similar proportion to waterborne As concentration at three salinity levels. This study proposed 135.3 ± 12.1 μg L−1 for salinities from 5 to 25 g L−1 as provisional safe As concentration. According to these results, the hypothesis that sustains an effect of low salinity on As acute toxicity and its bioconcentration capacity cannot be acceptable. Therefore, the information provided allows knowing the threshold levels of As in water to avoid ecological and economic losses.

Influence of salinity and linoleic or α-linolenic acid based diets on ontogenetic development and metabolism of unsaturated fatty acids in pike perch larvae (Sander lucioperca)

Combinations of nutritional requirements and husbandry rearing conditions during early ontogeny are poorly studied in pikeperch (Sander lucioperca). The substitution of marine oils with vegetable oils has reduced stress tolerance and caused neurophysiological changes in pike perch larvae, but effects of environmental cues are limited. Saline water influences on a range of physiological functions during early fish larval ontogeny and may affect FA metabolism, − elongation and desaturation - activity when given diets limited in LC PUFAs, but rich in shorter chain n-3 or n-6 PUFAs. Consequently, live Artemia differing in 18:2n-6 (LA) and 18:3n-3 (ALA) content by enrichment with sunflower oil (SFO) or linseed oil (LO) were fed to 10 days post hatch (DPH) larvae and reared up to isosmotic salinities (0, 5, 10 ppt) until 30 DPH. Larval tissue FA composition was examined at 15, 25 and 30 DPH. Besides, an in vivo assay was performed on 20 DPH larvae with 14C labelled FA including LA; ALA; 20:4n-6 (ARA); 20:5n-3 (EPA) or 22:6n-3 (DHA) to establish FA incorporation and metabolism. At 30 DPH, performance, digestive enzymatic activity, eicosanoid activity, skeletal anomalies and stress sensitivity were further evaluated. Results on larval FA profiles suggest a low desaturation and elongation capability over LA and ALA, with no significant effects of salinity or larval age on modulation of unsaturated fatty acid metabolism. In vivo assays revealed that regardless of salinity or diet, pikeperch possess a marked specificity to incorporate ARA and EPA compared to a poorer incorporation of DHA. Larvae exposed to a confinement stress test caused high acute mortality in all experimental groups except for a control group fed with Artemia enriched by a commercial DHA Selco emulsion. Growth performance was not significantly affected by salinity or dietary enrichment with SFO or LO, but influenced on larval enzymatic activity of pepsin, aminopeptidase, trypsin and alkaline phosphatase, while lipase activity was not significantly affected. Increased saline conditions significantly decreased hormonal prostaglandin eicosanoid PGE2, PGE3 activity with the highest activity at 0 ppt. The prevalence of severe skeletal anomalies was generally high, affecting over 75% of the larval population with negative effects by increase in salinity. The incidence of anomalies was higher on endochondral bones, namely maxillary, ranging from 58 to 83% of the population. These results agree well with those from expression of sox 9 and twist2 genes; involved in chondrocyte ossification and differentiation.

Disturbance in Na+ regulation in cells rich in mitochondria isolated from gills of the yellow clam Mesodesma mactroides exposed to copper under different osmotic conditions

Cells rich in mitochondria were isolated from gills of the seawater clam Mesodesma mactroides, incubated in isosmotic saline solution (840 mOsmol/kg H2O), and exposed (3 h) to environmentally realistic Cu concentrations (nominally: 0, 5, 9 and 20 μg/L). In cells exposed to 20 μg Cu/L, Cu accumulation, Na+ content reduction and carbonic anhydrase (CA) activity inhibition were observed, without significant changes in cell viability and Na+,K+-ATPase (NKA) activity. In the absence of Cu, cell viability and Cu content were reduced in hyposmotic media respect with the control, without changes in Na+ content and enzyme (CA and NKA) activities. In the presence of 5 or 9 μg/L Cu, cell Cu content was increased, especially at 670 mOsmol/kg H2O. Cell Na+ content and NKA activity were reduced after exposure to 20 μg/L Cu at 670 mOsmol/kg H2O. In turn, CA activity was dependent on Cu concentration, being significantly reduced in cells exposed to 9 and 20 μg/L Cu in both hyposmotic conditions. These findings indicate that Cu also negatively affects Na+ regulation in gill cells of the seawater clam M. mactroides, with Cu toxicity increasing at hyposmotic conditions. Also, they indicate that physiology is more important than water chemistry in predicting Cu toxicity in environments of changing salinity, pointing out CA activity as a potential biomarker of Cu exposure.

Activation of G Protein‐coupled Estrogen Receptor Promotes Endothelin‐dependent Natriuresis in Female Rats

The novel estrogen receptor, G protein‐coupled estrogen receptor (GPER), is a membrane‐bound receptor linked to acute signaling pathways. GPER activation elicits cardiovascular and nephroprotective effects against salt‐induced complications. However, its specific role in renal sodium handling is not yet defined. We hypothesized that activation of GPER in the renal medulla facilitates sodium excretion. Isosmotic saline was infused into the renal medullary interstitium (500 μl/h) of anesthetized male and female Sprague‐Dawley rats for an 80 min equilibration period and 20 min baseline urine collection period. Then, G1 (GPER agonist, 50 pmol/kg/min) or vehicle was infused into the renal medulla for an additional 20 min period. Compared with vehicle, G1 significantly increased urinary sodium excretion in females (from 0.6 ± 0.1 to 1.0 ± 0.1 μmol/min n=9, p<0.05). G1 did not change blood pressure or urinary potassium excretion in comparison with vehicle control (106 ± 3 vs. 105 ± 4 mmHg, 0.5 ± 0.1 vs. 0.4 ± 0.1 μmol/min, n=9). Medullary blood flow remained unchanged during these experiments. In males, G1 did not change urinary sodium excretion (from 0.6 ± 0.1 to 0.7 ± 0.1 μmol/min, n=9). No sex‐differences in medullary GPER mRNA expression was observed, suggesting that sex‐differences in G1 effects on sodium excretion could be related to GPER downstream signaling cascade. Given that endothelin‐1 (ET‐1) is a well‐established natriuretic factor that is regulated by sex and sex steroids, we hypothesized that GPER activation promotes natriuresis via an ET‐1‐dependent pathway. To test this idea, we studied the effect of medullary infusion of G1 after dual blockade of ETA and ETB receptors achieved by i.v. bolus injection of ABT‐627 (5 mg/kg) and A‐192621 (10 mg/kg), respectively. We found that the natriuretic response to medullary GPER activation in females was inhibited by dual blockade of ET‐1 receptors (from 0.5 ± 0.2 to 0.5 ± 0.2 μmol/min n=5). These data uncover a novel role for renal medullary GPER in promoting sodium excretion via an ET‐1‐dependent pathway in females, but not in males.Support or Funding InformationFunded by AHA 15POST25090329 to EYG and P01 HL136267 to DMP and JSPThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Salinity an Environmental “Filter” Selecting for Plant Invasiveness? Evidence from Indigenous Lepidium alyssoides on Chihuahuan Desert Shrublands

A better understanding of site-specific factors such as soil salinity that regulate plant invasions is needed. We conducted a 3-mo greenhouse study to evaluate the salinity responses of three local maternal sources of Lepidium alyssoides, which is an indigenous species shown to aggressively colonize disturbed shrubland sites in the southwestern United States, including those affected by high salinity and sodicity. Results indicated that there were little or no population effects on plant evapotranspiration (ET), growth, and tissue Na and Cl concentrations. Significant reductions in seedling growth and ET were largely independent of various isosmotic saline irrigation solutions that included NaCl, Na2SO4, and CaCl2, each at −0.1 MPa and −0.2 MPa, suggesting that ET and growth were controlled by solution osmotic potential. The combined Na and Cl concentrations in leaves were 9–10% of dry weight with no visible sign of injury. However, increasing leaf mortality and abscission as a proportion of total leaf production was observed in the high-salt treatments (−0.2 MPa), with a combined Na and Cl concentration reaching 16% with high NaCl. Under saline conditions, considerable foliage salt loads of this species could deposit high-salt litter to potentially alter a landscape to its own favor and to the detriment of other salt-sensitive species. Results of this study add to a limited quantitative database on site-specific salinity factors governing plant invasions by showing the potential for these populations to behave invasively under saline conditions and, thus, potential for soil salinity assessment to predict incipient populations. However, due to its halophytic traits and indigenous status, L. alyssoides may alternatively provide ecosystem services to salinized shrublands of the arid and semiarid southwestern United States.

Abstract 041: New Evidence for G Protein-coupled Estrogen Receptor as a Natriuretic Factor

Premenopausal women have a lower risk of cardiovascular and renal diseases compared to age-matched men. This protection includes fewer salt-dependent complications. We have shown that female rats have a more robust natriuretic capacity compared to males in response to increased dietary salt. The novel estrogen receptor, G protein-coupled estrogen receptor (GPER), is a membrane-bound receptor linked to acute signaling pathways. GPER activation elicits protective effects throughout the cardiovascular system. However, its role in sodium handling is not defined. We hypothesized that activation of GPER in the renal medulla stimulates sodium excretion. In female Sprague Dawley (SD) rats, isosmotic saline was infused into the renal medullary interstitium (500 μl/h) during a 60-80 min equilibration period and 20 min baseline urine collection period. This was followed by infusion of the GPER agonist G1 (50 pmol/kg/min) or vehicle into the renal medulla for two further 20 min periods. Compared with vehicle, G1 significantly increased urinary sodium excretion and urine flow (from 0.5 ± 0.1 to 0.9 ± 0.2 μmol/min and from 5.3±1.1 to 8.3±1.6 μl/min, respectively, n=6, p<0.05). Urinary potassium excretion and mean arterial pressure remained unchanged during the experiments (0.5 ± 0.1 vs. 0.4 ± 0.1 μmol/min and 108.6 ± 3.4 vs. 107.2 ± 5.1 mmHg, respectively, n=6). Immunohistochemical analysis of GPER revealed more predominant staining in both inner and outer renal medulla in female SD rats, compared to males. GPER appears to be predominantly expressed in interstitial cells. These data reveal that renal medullary GPER plays an important role in renal sodium handling and may account for the enhanced ability to handle increased dietary salt in females. Funded by AHA 15POST25090329 to EYG and P01 HL136267 to DMP

Osmoregulation and muscle water control of the Amazon fish Oscar Astronotus ocellatus (Cichlidae) when facing salinity stress

ABSTRACTSpecimens of Oscar Astronotus ocellatus from a fish farm were abruptly submitted to salt stress of 14 ppt and 20 ppt, for 3 and 8 h to determine their plasma osmolality. Muscle wet body mass change in vitro was analyzed from control freshwater animals. Fish in 14 ppt presented no osmolality distress even after 8 h. In 20 ppt, a slight increase (10%) in plasma osmolality was observed for both times of exposure when compared to control fish. Muscle slices submitted in vitro to hyper-osmotic saline displayed decreased body mass after 75 min, and slices submitted to hypo-osmotic saline displayed increased body mass after 45 min when compared to control (isosmotic saline). These results reinforce A. ocellatus’s euryhalinity. The fish were able to regulate its internal medium and tolerate 14 ppt, but presented an intense osmotic challenge and low muscle hydration control when facing salinities of 20 ppt.

The effects of environmental salinity on the growth and physiology of totoaba Totoaba macdonaldi and shortfin corvina Cynoscion parvipinnis.

Totoaba Totoaba macdonaldi and shortfin corvina Cynoscion parvipinnis, were acclimated and reared together at salinities of 0, 2, 5, 10, 20 and 35 for 56 days. Initial overall mean ± s.d. body masses of 67·6 ± 7·1 g T. macdonaldi and 37·3 ± 3·1 g C. parvipinnis increased to final overall masses of 217·4 ± 30·3 and 96·5 ± 16·5 g, respectively, at the end of the study. Totoaba macdonaldi was not able to tolerate salinities of 0 and 2 and C. parvipinnis of 0. In contrast, both species had 100% survival at salinities ≥ 10. Somatic growth was highest not at natural seawater salinity of 35, but at 10. Plasma osmolality ranged from 172·5 to 417·0 mOsmol kg-1 for T. macdonaldi and from 207·0 to 439·5 mOsmol kg-1 for C. parvipinnis and varied in direct proportion to salinity. The estimated isosmotic salinities of T. macdonaldi and C. parvipinnis were 12·3 and 13·4, respectively. Cynoscion parvipinnis reared at two had significantly lower plasma lysozyme activity (95·0 Units ml-1 ) than fish held at salinities from 5 to 35 (ranging from 215·0 to 355·0 Units ml-1 ), but without clear trends over this range. Blood neutrophil oxidative radical production (NBT) (ranging from 3·9 to 6·7 mg ml-1 ) had some significant differences among salinities, but these did not follow a clear pattern. For T. macdonaldi, neither lysozyme activity nor NBT was affected by salinity. Ash content of whole fishes varied directly and moisture content inversely, with salinity for both species.

Ovariectomy uncovers purinergic receptor activation of endothelin-dependent natriuresis.

We recently reported that natriuresis produced by renal medullary salt loading is dependent on endothelin (ET)-1 and purinergic (P2) receptors in male rats. Because sex differences in ET-1 and P2 signaling have been reported, we decided to test whether ovarian sex hormones regulate renal medullary ET-1 and P2-dependent natriuresis. The effect of medullary NaCl loading on Na+ excretion was determined in intact and ovariectomized (OVX) female Sprague-Dawley rats with and without ET-1 or P2 receptor antagonism. Isosmotic saline (284 mosmol/kgH2O) was infused in the renal medullary interstitium of anesthetized rats during a baseline urine collection period, followed by isosmotic or hyperosmotic saline (1,800 mosmol/kgH2O) infusion. Medullary NaCl loading significantly enhanced Na+ excretion in intact and OVX female rats. ETA+B or P2 receptor blockade did not attenuate the natriuretic effect of medullary NaCl loading in intact females, whereas ETA+B or P2 receptor blockade attenuated the natriuretic response to NaCl loading in OVX rats. Activation of medullary P2Y2 and P2Y4 receptors by UTP infusion had no significant effect in intact females but enhanced Na+ excretion in OVX rats. Combined ETA+B receptor blockade significantly inhibited the natriuretic response to UTP observed in OVX rats. These data demonstrate that medullary NaCl loading induces ET-1 and P2-independent natriuresis in intact females. In OVX, activation of medullary P2 receptors promotes ET-dependent natriuresis, suggesting that ovarian hormones may regulate the interplay between the renal ET-1 and P2 signaling systems to facilitate Na+ excretion.

Mesodesma mactroides Gill Cells Exposed to Copper: Does Hyposmotic Saline Increase Cytotoxicity or Cellular Defenses?

Gill cells of filter feeding mollusks have cellular defense mechanisms, such as multixenobiotic resistance (MXR), that allow them to extrude possible contaminants. To analyze the cytotoxicity and cellular defenses of gills in the clam Mesodesma mactroides, gill cells were exposed to copper in both iso- and hyposmotic solutions. Analysis of MXR activity by fluorescence microscopy showed that hyposmotic saline activated defenses, whereas the presence of copper in isosmotic solution inhibited the activation of defenses. Cell viability was decreased in cells exposed to copper in isosmotic saline, but not in cells exposed to hyposmotic saline. We conclude that when cells cannot defend themselves due to decreased MXR, cell death occurs. In addition, gill cells under hyposmotic conditions have a greater capacity for defense and a lower rate of cellular mortality than when they are maintained under isosmotic conditions.

Abstract 095: Ovariectomy Restores Purinergic Receptor Activation of Endothelin-dependent Natriuresis

We have recently reported interplay between renal medullary endothelin-1 (ET-1) and purinergic (P2) systems, which play central roles in controlling Na + homeostasis in male rats. Evidence suggests that sex hormones regulate ET-1 and P2 systems. To test whether activation of the renal medullary P2 receptors promotes ET-dependent natriuresis in females and whether ovariectomy (OVX) modulates this potential interaction, we studied the effect of medullary NaCl loading on Na + excretion in adult intact female and OVX SD rats in the presence and absence of P2 or ET receptor antagonism. Isosmotic saline (284 mOsmol/kg H 2 O) was infused into the renal medullary interstitium during a baseline urine collection period, followed by isosmotic or hyperosmotic saline (1800 mOsmol/kg H 2 O) infusion. Blood pressure, renal blood flow, urine Na + , K + and osmolality were measured. Medullary NaCl loading significantly enhanced Na + excretion in intact females and OVX (from 0.8±0.2 to 6.2±1.6 and from 0.7±0.1 to 5.6±0.8 μmol/min, respectively, n=6-8, p<0.05). The natriuretic effect of NaCl loading in intact females was not attenuated by P2 or ET receptor blockade. Whereas, intramedullary infusion of the P2 receptor antagonist, suramin, inhibited the natriuresis induced by medullary NaCl loading in OVX (from 0.4±0.2 to 0.9±0.4 μmol/min, n=6). Additionally, combined ET A/B receptor blockade (ABT-627 + A-192621) abolished the natriuretic response to medullary NaCl load in OVX rats (from 0.2±0.1 to 1.4±0.7 μmol/min, n=4). Activation of medullary purinergic (P2Y 2/4 ) receptors by UTP infusion had no significant effect in intact females, but enhanced Na + excretion in OVX rats (from 0.5±0.1 to 2.3±0.8 μmol/min, n=5, p<0.05). Combined ET A/B receptor blockade significantly inhibited the natriuretic response to UTP observed in OVX rats. These data suggest that increased medullary NaCl loading induces ET-independent and P2-independent natriuresis in intact females. In OVX, activation of medullary P2 receptors promotes ET-dependent natriuresis, similar to our previous findings in male rats and suggests that OVX restores the interplay between the renal ET-1 and purinergic (P2) signaling systems to facilitate Na + excretion. Funded by AHA 15POST25090329 to EYG and P01 HL95499 to DMP

Molecular performance of Prl and Gh/Igf1 axis in the Mediterranean meager, Argyrosomus regius, acclimated to different rearing salinities.

Aquaculture industry in the Mediterranean region exhibits a growing interest for the Mediterranean meager Argyrosomus regius. Some preliminary works showed a good growth performance of the species in nearly isosmotic salinities. However, the patterns of alteration of prolactin (Prl) as well as growth hormone (Gh)/insulin growth factor-1 (Igf1) axis at the molecular level are not yet described in this species. Therefore, we cloned and sequenced partial cDNAs for pituitary prolactin (prl) and growth hormone (gh), hepatic insulin-like growth factor (igf1), and β-actin (actb). Expression patterns of these transcripts were tested in juveniles of A. regius acclimated to four different environmental salinities: (1) 5‰ (hyposmotic); (2) 12‰ (isosmotic); (3) 38‰ (hyperosmotic; seawater control); and (4) 55‰ (extremely hyperosmotic). All investigated transcripts shared high sequence identities with their counterparts in other perciformes. prl mRNA levels showed inverse pattern with increasing salinities. gh mRNA enhanced significantly in both 12 and 55‰ salinity groups in comparison with the control group, while igf1 showed its maximum expression levels under the nearly isosmotic environment. The results indicated clear sensitivity of prl, gh and igf1 to changes in environmental salinity, which can possibly control the euryhalinity capacity of this species.

Activation of purinergic receptors (P2) in the renal medulla promotes endothelin-dependent natriuresis in male rats.

Renal endothelin-1 (ET-1) and purinergic signaling systems regulate Na(+) reabsorption in the renal medulla. A link between the renal ET-1 and purinergic systems was demonstrated in vitro, however, the in vivo interaction between these systems has not been defined. To test whether renal medullary activation of purinergic (P2) receptors promotes ET-dependent natriuresis, we determined the effect of increased medullary NaCl loading on Na(+) excretion and inner medullary ET-1 mRNA expression in anesthetized adult male Sprague-Dawley rats in the presence and absence of purinergic receptor antagonism. Isosmotic saline (NaCl; 284 mosmol/kgH2O) was infused into the medullary interstitium (500 μl/h) during a 30-min baseline urine collection period, followed by isosmotic or hyperosmotic saline (1,800 mosmol/kgH2O) for two further 30-min urine collection periods. Na(+) excretion was significantly increased during intramedullary infusion of hyperosmotic saline. Compared with isosmotic saline, hyperosmotic saline infused into the renal medulla caused significant increases in inner medullary ET-1 mRNA expression. Renal intramedullary infusion of the P2 receptor antagonist suramin inhibited the increase in Na(+) excretion and inner medullary ET-1 mRNA expression induced by NaCl loading in the renal medulla. Activation of medullary P2Y2/4 receptors by infusion of UTP increased urinary Na(+) excretion. Combined ETA and ETB receptor blockade abolished the natriuretic response to intramedullary infusion of UTP. These data demonstrate that activation of medullary P2 receptors promotes ET-dependent natriuresis in male rats, suggesting that the renal ET-1 and purinergic signaling systems interact to efficiently facilitate excretion of a NaCl load.

Sex Differences in Renal Inner Medullary ET‐1 Gene Expression Levels with Increasing Medullary Osmolality

We previously reported that exposing the renal medulla to hyperosmotic solutions enhances urinary ET‐1 excretion in male rats. We have also seen that female rats have a more robust renal ET‐1 natriuretic capacity compared to males. Therefore, we determined whether intramedullary infusion of hyperosmotic saline has a differential effect on ET‐1 gene expression in inner medullas from anesthetized male and female rats. Isosmotic saline (284 mosmol/kgH2O) was infused into the renal medullary interstitium (500 μl/h) during a 60 min equilibration period and 30 min baseline urine collection period, followed by isosmotic or hyperosmotic saline (1800 mosmol/kgH2O) for two further 30 min periods. At the end of each experiment, the renal inner medulla was isolated for ET‐1 mRNA assessment using the real‐time quantitative polymerase chain reaction (RT‐PCR) technique. Compared with isosmotic saline, hyperosmotic saline infused in the renal medulla caused significant increases in urine flow in both male and female rats (from 6.3±0.9 to 12.2±1.7 and from 8.2±1.3 to 15.0±2.8 μl/min, respectively). Sodium excretion was also significantly enhanced, in both males and females (from 0.6±0.1 to 8.3±1.9 and from 0.9±0.2 to 5.8±1.0 μl/min, respectively). Inner medullary ET‐1 expression in male rats was significantly increased after 60 min of medullary interstitial infusion of hyperosmotic saline (from 1.0± 0.1 to 1.4± 0.1 fold change, p<0.05). In contrast, ET‐1 expression did not change with medullary hyperosmotic infusion in females. These data indicate that an increase in renal inner medullary ET‐1 could play a more important role in the diuretic and natriuretic response to intramedullary hyperosmolality in male compared to female rats.

Different abilities to regulate tissue hydration upon osmotic challenge in vitro, in the cephalopods Octopus vulgaris and O. insularis

The spatial distribution of cephalopods is influenced by salinity and temperature. In marine osmoconformers, one reason for different spatial distributions maybe the putative distinct capacity to regulate tissue hydration. Adult Octopus vulgaris (n = 6) and O. insularis (n = 6) were obtained by divers from sites along the southern and northeastern Brazilian coasts, respectively. In the laboratory, octopuses were acclimated to full-strength seawater (salinity 34), for 5–10 days. They were then anesthetized (10 min in 4 °C seawater), a portion of the second right arm was removed, and cut into three portions. Tissues were placed in control isosmotic saline (osmolality 1072 mOsm/kg H2O). Fragments were weighed and transferred to either isosmotic, hyposmotic (50%), or hyperosmotic (150%) salines, and their weight was observed for 120 min. Tissue from both species maintained their hydration/weight following the hyposmotic shock, but differed in their response to the hyperosmotic challenge, where hydration remained unchanged in O. insularis, but was significantly reduced in O. vulgaris. This result could partially explain why O. insularis is more abundant than O. vulgaris throughout the shallow reefs and tide pools in the warmer and salty tropical waters of the northeastern Brazilian coast.