Effects of hypoxia on osmotic and ionic regulation in the brown shrimp Crangon crangon (L.) from brackish water

When exposed to hypoxia (P_wO₂, <P_cr) and low salinity conditions, the shrimp, Crangon crangon (L.) shows a progressive loss of blood chloride until a new, stable value, still higher than that of the medium, is reached. Simultaneously, circulating levels of calcium progressively increase. Under identical experimental conditions, circulating levels of sodium and magnesium and the blood total osmolarity (Δ °C) are unchanged. The possible explanations for such changes are considered along with their adaptive significance.     

Dietary salt intake and its relevance to ionic regulation in freshwater salmonids

Dietary sodium intake for freshwater salmonids feeding in the wild (invertebrate diet) or in captivity (pellet diet) was calculated and compared with published branchial sodium influx values. Dietary sodium intake (mmol kg⁻¹ per month) increases from winter minimum values of 5 and 30-40 to reach maximum values in summer of 175 and 240 for invertebrate and pellet diet, respectively. In summer, dietary sodium intake for fish feeding in the wild was of the same magnitude as branchial sodium influx. The implications of dietary sodium intake for sodium balance in freshwater fish are discussed.     

Loss of ionic and osmotic regulation in Chara internodal cells in concentrated KCl solutions

Intact internodal cells of Chara are known to maintain their osmotic pressures at constant levels in artificial pond water at room temperature. Cell fragments with osmotic pressures higher and those cell fragments with osmotic pressures lower than the original, both of which are prepared from intact internodal cells using transcellular osmosis and ligation with threads, can also return their osmotic pressures to the original level within a week in artificial pond water. These regulatory phenomena are realized mainly by extrusion of K⁺ and Cl⁻ in the cytoplasm and/or vacuole or by absorption of K⁺ and Cl⁻ from the external solution. According to the electrochemical potential difference calculated for K⁺ between the vacuole and the external solution, the cells should be able to maintain these regulatory functions even in 50–100 m M KCl+ 1 m M CaCl₂ solutions. However, novel phenomena were observed when they were immersed in such concentrated KCl solutions. To maintain electroneutrality, their osmotic pressures increased up to ca l MPa in 2 days due to absorption of K⁺ and Cl⁻ and many gradually died over time. Ionic and osmotic reguratory functions of Chara cells were lost when they were immersed in 50–100 m M K-salt solutions containing 1 m M Ca²⁺.     

Effect of temperature on osmotic and ionic regulation in goldfish,Carassius auratus L.

Summary Urine flow increased with acute temperature increases and showed temperature acclimation. When measured at 20 °C the urine flow of 10 °C acclimated fish was 3.2 times greater than the urine flow of 30 °C acclimated fish. In fish acclimated to 24 °C renal reabsorption of Na and Cl was independent of temperature over an intermediate range of temperatures (14–24 °C) but near the lower lethal temperature (6.5 °C) renal Na and Cl reabsorption was inhibited. Water permeability of the renal tubules was not affected by acute temperature change between 6.5 and 24 °C. Urine osmolality and urine Na, K and Cl concentrations showed nearly perfect temperature compensation in fish acclimated to 10 °C and 30 °C. The rate of renal excretion of Na and Cl showed temperature acclimation in that Na and Cl ecxretion measured at 20 °C was 7 to 8 times greater in 10 °C acclimated fish than in 30 °C acclimated fish. The rate of excretion of Na and Cl measured at 30 °C in 30 °C acclimated fish was approximately 1.7 times the rate of excretion measured at 10 °C in 10 °C acclimated fish.The branchial uptake of Na, measured in tap water, of fish acclimated to 10, 20 and 30 °C in demineralized water increased with acute increases in temperature. When the three acclimation groups were compared at an intermediate temperature (20 °C), the 10 °C acclimated group showed the highest rate of net uptake, and the 30 °C group the lowest rate of uptake. This apparent temperature acclimation of Na uptake was correlated with differences in the plasma Na concentration of the three acclimation groups. Plasma Cl concentrations were also correlated with acclimation temperature in fish acclimated in demineralized water, but the rate of net Cl uptake was considerably less than that for Na. Sodium and Cl uptake in fish which had been acclimated in tap water was very variable and was not clearly affected by acute changes in temperature. Uptake of Na and Cl by fish held in tap water did not show temperature acclimation. The difference between uptake and excretion of fish acclimated in tap water was not significantly different from zero, indicating that the fish were in salt balance.The study was supported by National Institutes of Health Grant GM 16932-02 to Dr. Bodil Schmidt-Nielsen. I am grateful to Dr. Schmidt-Nielsen for many useful discussions during the course of this work.     

The regulation of osmotic and ionic balance in fish reproduction and in the early stages of ontogeny

On the basis of the modern literature data we analyzed the influence of the level of salt concentration and ion composition in a fish habitat during the processes of reproduction. The results of studies of the mechanisms of the reaction of fish to gamete hypo- and hyperosmotic stimulus in the external aqueous environment, as well as the role of mineral and organic osmolytes in the adaptation of mature eggs of fishes in the external environment, depend on the hydrochemical and hydrological conditions of the spawning grounds. The paper provides information about the features of the endocrine regulation of oocyte maturation in fish spawning in different hydrological conditions and the importance of humoral factors in the pathological process of the maturation of fish oocytes. The main scientific and practical aspects of the formation of the phys mechanisms that regulate the water-salt balance is the early ontogeny of fishes are discussed.     

Osmotic and ionic regulation during hypoxia in the medicinal leech, Hirudo medicinalis L.

The concentrations of inorganic and organic ions and osmolality in the blood of the medicinal leech, Hirudo medicinalis, were determined during normoxia and hypercapnic and hypocapnic hypoxia. In normoxic animals, the blood sodium concentration was 124.5 +/- 4.2 mmol/l and the total cation concentration was 132.2 +/- 4.3 mEq/l (mean +/- S.D.). Major anionic compounds were chloride (40.8 +/- 1.6 mmol/l), bicarbonate (8.4 +/- 1.3 mmol/l), and organic anions (42.5 +/- 2.3 mEq/l). Among the latter, malate accounts for 30.4 +/- 2.2 mEq/l. The nature of the remaining anion fraction, which balances cation and anion concentrations in leech blood, remains unknown. Within 96 h of hypercapnic hypoxia, the amount of organic osmolytes in leech tissue increased from the control level of 56.6 +/- 9.1 to 158.3 +/- 19.5 mumol/g dry weight. An even higher amount of organic acids was accumulated within 96 h of hypocapnic hypoxia (218.0 +/- 53.7 mumol/g dry weight). A possible reason for this is that lactate, which is a major end-product of hypocapnic hypoxia, cannot be excreted to the external medium as easily as propionate. The accumulation of blood organic acids generating osmotic stress in the animals was compensated by an equimolar decrease in sodium and chloride ion concentrations. In hypercapnic animals these changes resulted in a constant osmotic concentration of the blood (200 mosmol/kg H2O) during the experimental period. Between 24 and 96 h of hypocapnic hypoxia, however, the increase in the osmotic gradient between animal and medium was correlated with further net water uptake and the obvious deterioration of the volume- and ion-regulatory mechanisms in these animals.     

Effect of elevated temperature on osmotic and ionic regulation in a salt-tolerant caddisfly from Death Valley,California

The effects of temperature (8–10 or 20°C) on regulation of haemolymph osmotic and ionic concentrations were investigated over a range of salinities (0–25‰) in fifth-instar larvae of the Death Valley caddisfly Limnephilus assimilis. At low temperatures, levels of chloride and sodium in the haemolymph are regulated over a wide range of salinities corresponding to the salinities at which larvae occur in nature and at which they can complete development into adults. In contrast, haemolymph osmolality is constant at low salinities (<14‰) but approaches conformity with the medium at higher salinities. High temperature reduces the larva's ability to maintain low chloride concentrations in its haemolymph and also leads to a reduction in haemolymph osmotic pressure; thus, at high temperatures ions account for more of the haemolymph osmotic concentration than at low temperatures. These data suggest that the absence of larvae from thermal pools and from all Death Valley waters in summer can be explained by the effects of high water temperatures on hydromineral regulation.     

Adaptive patterns of osmotic and ionic regulation, and the invasion of fresh water by the palaemonid shrimps

To evaluate trends in the osmoregulatory behavior of neotropical, palaemonid shrimps, we investigated osmotic and ionic regulatory patterns in five species of Palaemon or Macrobrachium. The species' life histories depend on saline water to differing degrees, their habitats ranging from the marine/intertidal (P. northropi), through estuaries (P. pandaliformis) to coastal, freshwater streams (M. olfersii, M. potiuna) and inland, continental river systems (M. brasiliense). Hemolymph osmolality, chloride, sodium and magnesium concentrations were measured in shrimps exposed to experimental media ranging from fresh water (<0.5 per thousand ) to concentrated seawater (42 per thousand ) for up to 10 days. The marine and estuarine Palaemon species exhibit well-developed hyper/hypo-osmotic, sodium and chloride regulatory capabilities in mid-range salinities, tending to hyperconform in low salinities. The freshwater Macrobrachium species show variable hyperosmotic, sodium and chloride regulatory capacities, tending to hypoconform or unable to survive at higher salinities. All species hyper-regulate magnesium in fresh water, but hyporegulate strongly in saline media. Palaemonids from the saline habitats show the strongest osmoregulatory capabilities, and fresh water may have been gradually invaded by ancestral species with similar regulatory capacity. However, this regulatory plasticity has been lost to varying degrees in extant freshwater species.     

Some aspects of osmotic and ionic regulation in Adriatic sturgeon Acipenser naccarii. I: Ontogenesis of salinity tolerance

The salinity tolerance of various early life stages (prelarvae, larvae and fry) of the Adriatic sturgeon ( Acipenser naccarii ) was investigated using acute exposures in a 96h-LC₅₀ test. The results were compared with a series of parallel observations on the morphological development of the osmoregulatory organs. The highest salinities tolerated by prelarave and larvae were approximately iso-osmotic with sturgeon plasma. Once, however, the organs involved in homeostatic osmoregulatory mechanisms in the adult had developed (renal-branchial-gut system), the sturgeon was able to switch from hyper-osmoregulation to hypo-osmoregulation. Nevertheless, at the most advanced age tested (150 days old), water at a salinity of approximately 20% appeared to be the upper threshold for tolerance of acute exposure by this species.     

Environmental and climatic factors affecting winter hypoxia in a freshwater lake: evidence for a hypoxia refuge and for re-oxygenation prior to spring ice loss

Hydrobiologia - Low dissolved oxygen, or hypoxia, is a common phenomenon in ice-covered lakes in winter. We measured dissolved oxygen (DO) before, during, and after ice-over to characterize the...     

Osmotic and ionic regulation in Nitella

When the osmotic value of an internodal cell of Nitella flexiliswas modified by the method of transcellular osmosis, the normalosmotic value was chiefly restored by the release or absorptionof K⁺. The release or uptake of Na⁺ was observed only when themodification of osmotic value was significant. Both the uptakeand release of K⁺ were linearly dependent on the degree of modificationof the osmotic value. The effectiveness of alkali metal cationsin restoring the osmotic value in cells of lower osmotic valueswas in the order K⁺>Rb⁺>Na⁺, Cs⁺>Li⁺. The absorptionof K⁺ by cells of lower osmotic values depended strongly ontemperature, while the release of K⁺ from cells of higher osmoticvalues did not. To clarify whether the Nitella cell regulates the osmotic valueor regulates the concentration of K⁺ in the vacuole, the cellsap was exchanged for artificial cell saps whose osmotic valuesand ionic concentrations were varied independent of each other.It was shown that in Nitella two regulating mechanisms are operating,one which regulates the osmotic value of the cell sap irrespectiveof the level of vacuolar K⁺ (0.1–140 mM) and another whichregulates the vacuolar K⁺-level when it is abnormaly high (>160mM). Both mechanisms are assumed to operate in order to keepthe concentration of K⁺ in the cytoplasm at a constant level.The presence of Na⁺ (0–100 mM) and Ca²⁺ (5–40 mM)did not affect the movement of K⁺ during osmoregulation. ¹Present address: Sanki Engineering Limited, Nagaokakyo, Kyoto,Japan. (Received December 19, 1973; )     

Acid brine shrimp: Metabolic strategies in osmotic and ionic adaptation

Acid salt lakes are found in several regions of Australia but are uncommonly abundant in the Yilgarn Block area of southwestern Australia. The chemical properties of the acid salt lakes are in general similar to those of shallow ephemeral alkaline salt lakes found in adjacent regions except for having a higher hydrogen ion concentration and an absence of carbonate and bicarbonate ions. The Australian brine shrimp, Parartemia, is the major zooplankter living in these salt lakes. Present investigation on two species of larval Parartemia reveal P. zietziana nauplii having high salt tolerance (LD₅₀ > 225 TDS) but a narrow pH range with an optimum lying near pH 8. In contrast, P. contracta collected from acid salt lakes had a more restricted salt tolerance (LD₅₀ < 100 TDS) but a wider range of pH tolerances with substantial survival below pH 3.5. Both species, P. zietziana and contracta, when placed in ouabain-laden salines, demonstrated decreased survival and indirectly indicated the presence of a ouabain-sensitive sodium pump. Direct enzymatic assay of the sodium pump (Na, K ATPase) in nauplii of P. zietziana gave specific activity values of 2.9 µM Pi/hr/mg protein supporting our working hypothesis that the nauplii of Parartermia have an osmoregulatory system similar to that found in larval Artemia which is dependent upon having large quantities of ATP to support the sodium pump. In Artemia larvae, the production of ATP is enhanced through a facultative pathway involving an aerobic glycolysis linked C-4 dicarboxylic shunt. The major CO₂ source for the C-4 acid shunt for alkaline brine shrimp has been found to be the dissolved bicarbonate/carbonate ions. In highly acidic saline lakes, these ions are missing. If acid brine shrimp are to survive in low pH ephemeral saline lakes, they must have evolved an additional proton pump and devised a mechanism to produce ATP from endogenous CO₂ substrates.     

Tonoplast fine structure and osmotic regulation in Porphyra umbilicalis

In Porphyra, an intertidal red alga, the fine structure of the tonoplast was studied by freeze-fracture electron microscopy. It was shown that density and size of intramembraneous particles on the protoplasmic fracture face vary with external osmotic potential. The frequency of particles grouped in size classes (calculated per cell) increases with increasing osmotic stress and shows a maximum in 3 to 4 x artificial seawater medium ASP₁₂. It is concluded that the intensity of tonoplast transport, which probably is enhanced with increasing osmotic stress from 1 to 4 x media, is most likely correlated with a change in membrane fine structure of the tonoplast.