Patterns of changes in sodium content in plasma and erythrocytes of freshwater fish at stress

Experiments described in the present study revealed that the sodium concentration in the blood plasma drops to 30% relative to the initial level in roach (Rutilus rutilus) and to 27% in bream (Abramis brama) during a few hours of the initial stage of stress. The transport from erythrocytes counteracts plasma hyponatremia and results in the decrease in erythrocyte sodium to 62% in roach and 61% in bream. These data contradict the earlier published hypothesis on the stress-induced stimulation of counter-transporting Na⁺/H⁺ exchanger by catecholamines and consequent elevation of erythrocyte sodium aimed at increase in oxygen-carrying capacity. At stress, increased demands of organism for oxygen are compensated by the additional introduction of erythrocytes from depot to blood.     

Metabolic aspects of temperature adaptation by fish

During 8-hour acclimation to changes in the water temperature by 10 degrees within the range of 20-30 degrees C the metabolic compensation of the temperature effects in the carp liver mitochondria is manifested at the level of thermogenesis, activity of succinate dehydrogenase and rate of oxidative phosphorylation. No temperature compensation is found for the activity of cytochromoxidase, ATPase, rate of nonphosphorylating oxidation, content of ATP, phosphorus and calcium in the mentioned organelles.     

Evolutionary temperature adaptation of fish sarcoplasmic reticulum

Summary Sarcoplasmic reticulum has been isolated from the white muscle of 15 species of teleost fish adapted to diverse thermal environments. Evidence has been obtained that the Ca²⁺-dependent ATPase of fish sarcoplasmic reticulum has undergone evolutionary modification for function at different temperatures. Compared with tropical fish, cold adapted species have higher rates of Ca²⁺ transport and Ca²⁺-ATPase activities at low temperatures. Most species have linear Arrhenius plots over the temperature range 0–30°C. Activation enthalpies (H ) of the ATPase ranged from 53–190 kJ mol^–1 and were positively correlated with environment temperature. Activation entropy (S ) varied from negative values in cold adapted species to positive values in tropical fish.In contrast to the Ca²⁺-ATPase, the basal ATPase of fish sarcoplasmic reticulum showed no relationship between either ATPase activity or thermodynamic activation parameters and environmental temperature.Only the Ca²⁺-dependent ATPase is coupled to Ca²⁺ transport. The percentage of total ATPase activity which is Ca²⁺ activated is higher at low temperatures in cold than in warm adapted species. For example, ratios of Ca²⁺-dependent/total ATPase at 2°C varied from 80–98% in Arctic, Antarctic and North Sea species to only 2–50% in various tropical fish. Above 20°C, similar ratios in the range 80–98% were obtained for all species. The nature of the basal ATPase and mechanisms of temperature adaptation of fish sarcoplasmic reticulum are discussed.Abbreviations ET environmental temperature - EGTA ethylene glycol-bis (-aminolethyl ether)-N, N-tetraacetic acid - HEPES N-2-hydroxylpiperazine-N-2-ethanesulfonic acid - SR sarcoplasmic reticulum     

Involvement of brain gangliosides in temperature adaptation of fish

The ganglioside pattern of goldfish brain was investigated after adaptation (acclimatization, acclimation) to different temperatures. Adaptation at lower ambient temperature causes a higher proportion of polysialogangliosides to be formed in fish brain.     

Microcirculatory changes during chronic adaptation to hypoxia

Microcirculatory changes in the window chamber preparation in Syrian golden hamsters, secondary to chronic hypoxia adaptation, are presented herein. Adaptation was attained by keeping animals in a 10% oxygen environment for 1 wk and 5% the following week. The following groups were studied: group 1, adapted to chronic hypoxia and kept in a 5% oxygen environment throughout the experiment; group 2, adapted to chronic hypoxia and kept in a 21% oxygen environment 24 h before and during the experiment; and group 3, control. Adaptation caused venule enlargement and hematocrit increase (68.6 +/- 2.44 in group 1, 70 +/- 2.66 in group 2, and 43.27 +/- 2.30 in group 3; P < 0.05). Whereas heart rate decreased in adapted animals, blood pressure remained constant. Group 1 presented alkalosis, hypocapnia, and hypoxemia. The adapted groups had decreased blood flow velocity in arterioles and veins. We found no difference in microvasculature oxygen tension between groups 2 and 3; however, the number of capillaries with flow was markedly reduced in group 1 but significantly increased in group 2. Our findings suggest that, as an adaptation to hypoxia, erythropoiesis may prove beneficial by increasing blood viscosity and shear stress, leading to vasodilatation, in addition to the increase in oxygen-carrying capacity. Calculations show that oxygen extraction in the tissue of the window chamber model was significantly lowered in adapted animals breathing 5% oxygen, but was unchanged from the control when breathing 21% oxygen, even though blood hemoglobin content was increased from 14.5 +/- 0.07 g/dl at control to 21.04 +/- 1.24 g/dl in the adapted animals (P < 0.05).     

Morphofunctional changes in the pineal gland during adaptation to hypothermia

The influence of hypothermal stress (+4 degrees during 3 h) on the ways of serotonin metabolism in pineal gland and its structure has been studied in dynamics on adult male Wistar rats. It has been revealed that melatonin-producing epiphyseal function suffers from phase changes in dynamics of adaptation--significant rising during 15 min. after beginning of the experiment, rehabilitation up to normal--in 30 min, and fast suppressing--in 3 hrs. Suppressing of the functional pineal activity is not due to switched serotonin metabolism with melatonin and new indoles release, but to a partial pinealocytes breaking from their active function.     

The systematics of fish metabolic response to changes in hydrogen ion concentrations in the pH gradient field

It has been revealed that a change in water pH during free swimming of fish in the pH gradient field optimizes fish growth and their physiological state. Fish locomotor activity rises. However, despite additional activity, the fish energy budget improves, energy consumption decreases weight gain, and the efficiency of food utilization for growth increases. The changes in growth parameters and in energy caused by swimming in the pH gradient field are closely correlated. This is evidence of the systemic character of fish response to changes in the pH of water. The changes in one metabolic parameter can be used to assess other parameters. The results of this study should be considered for the improvement of juvenile fish farming techniques.     

The growth and phospholipid composition of a moderately halophilic bacterium during adaptation to changes in salinity

The effect of a sudden change in NaCl concentration of the medium on the time course of alterations in growth rate and phospholipid composition of the moderately halophilic bacteriumVibrio costicola has been investigated. This organism and other moderate halophiles are known to contain a larger proportion of negatively charged phospholipids in their membranes when grown at higher salt concentrations. We show for the first time that the change in proportion of phosphatidylglycerol, relative to phosphatidylethanolamine, which occurs after a shift from 1M to 3M NaCl, or vice versa, is essentially completed during that period immediately following the salt shift when growth is zero or very slow, and before the cells have adopted the growth rate appropriate to the new salt concentration. It appears, therefore, that the alteration in membrane phospholipid composition may be a necessary physiological response for adaptation to change in salinity.     

Molecular mechanisms of temperature adaptation in fish myofibrillar adenosine triphosphatases

Summary Studies have been carried out on the Mg²⁺ Ca²⁺-myofibrillar ATPase from the muscles of fish adapted to different environmental temperatures. The thermal stability of the ATPase is strongly correlated with mean habitat temperature. Activities of Antarctic fish ATPases are significantly higher at low temperatures than those of temperate and tropical water species. The effects of ionic strength on ATPase activity have also been studied. The Gibbs free energy of activation (G ^#) was found to increase and enzyme activity decrease with increasing ionic strength within the physiological temperature range of each species. Significantly lower values of G ^#, of around 1 Kcal/mole, are obtained for the ATPase of cold-adapted compared to tropical fish. Enthalpic and entropic activation energies were also reduced in the cold adapted ATPases. It is postulated that the reduction of the enthalpic activation term in the cold adapted enzyme confers the advantage of reducing the temperature sensitivity of the rate limiting step thus partly compensating for the low heat content of the cellular environment. Possible molecular mechanisms of temperature compensation in fish myofibrillar ATPase are discussed.     

Kinetics and thermodynamics of ouabain binding by intact turkey erythrocytes: effects of external sodium ion, potassium ion, and temperature

The kinetics of association and dissociation for the ouabain-Na+,K+- dependent ATPase complex have been studied in intact turkey erythrocytes as a function of external Na+ concentration, K+ concentration, and temperature. At free ligand concentrations substantially exceeding the concentration of available binding sites, the association reaction exhibits pseudo-first-order kinetics with an association rate constant (k1) that is conveniently determined over a wide range of temperatures (5-37 degrees C). The dissociation reaction exhibits strict first-order kinetics with a dissociation rate constant (k-1) that has the unusual property, in the turkey cell, of being sufficiently great to permit its direct determination even at temperatures as low as 5 degrees C. Values for the equilibrium binding constant for the ouabain-ATPase complex (KA) predicted from the ratio of the association and dissociation rate constants agree closely with independently measured values of KA determined directly under conditions of equilibrium binding. KA is a sensitive function of the composition of the external ionic environment, rising with increasing Na+ concentration and falling with increasing K+ concentration. These changes in KA are shown to be quantitatively attributable to changes in the rate constant k1, k-1 in contrast being unaffected at any given temperature by even very large changes in Na+ or K+ concentration. Arrhenius plots of k1 and k-1 both yield straight lines over the entire temperature range corresponding to activation energies for association and dissociation of 29.5 and 24.2 kcal/mol, respectively. These observations have made it possible to calculate the following standard values for the ouabain binding reaction in the presence of 150 mM Na+: delta G degree = -9.8 kcal/mol; delta H degree = +5.3 kcal/mol; delta S degree = +48.7 cal/degree/mol. The large positive value of delta S degree presumably reflects a highly ordered configuration of the ouabain-free ATPase molecule that is lost upon ouabain binding and that "drives" the reaction despite the positive value of delta H degree.     

Metabolic changes induced during adaptation of Saccharomyces cerevisiae to a water stress

When exponentially growing Saccharomyces cerevisiae was transferred from a normal high water activity growth medium (a_w 0.997) to a medium containing 8% NaCl low water activity growth medium (a_w 0.955), glycerol accumulation during the first eight hours of the adaptation was both retarded and greatly diminished in magnitude. Investigation of the underlying reasons for the slow onset of glycerol accumulation revealed that not only was overall glycerol production reduced by salt transfer, but also the rates of ethanol production and glucose consumption were reduced. Measurement of glycolytic intermediates revealed an accumulation of glucose-6-phosphate, fructose-6-phosphate, fructose 1,6 bisphosphate and phosphoenolpyruvate in S. cerevisiae 3 to 4 h after transfer to salt, suggesting that one or more glycolytic enzymes were inhibited. Potassium ions accumulated in S. cerevisiae after salt transfer and reached a maximum about 6 h after transfer, whereas the sodium ion content increased progressively during the adaptation period. The trehalose content also increased in adapting cells. It is suggested that inhibition of glycerol production during the initial period of adaptation could be due to either the inhibition of glycerol-3-phosphate dehydrogenase by increased cation content or the inhibitin of glycolysis, glycerol being produced glycolytically in S. cerevisiae. The increased accumulation of glycerol towards the end of the 8-h period suggests that the osmoregulatory response of S. cerevisiae involves complex sets of adjustments in which inhibition of glycerol-3-phosphate dehydrogenase must be relieved before glycerol functions as a major osmoregulator.     

Evolutionary temperature adaptation and the calcium regulation of fish actomyosin ATPases

Summary Actomyosins have been isolated from the white skeletal muscles of fish inhabiting thermal environments with characteristically low seasonal temperature variations for example, Antarctica, arctic rivers and the equatorial oceans.Calcium regulation of actomyosin ATPase was correlated with environmental temperature. Increased assay temperature resulted in a progressive loss of calcium sensitivity. This occurred at lower temperatures in the more cold adapted species.In general cold adapted ATPases have lower activation enthalpies (H ) and higher activities at low temperatures than their tropical counterparts. In contrast to environmental temperature acclimation (Johnston, 1979) calcium regulatory proteins of stenothermal species were not directly involved in the temperature adaptation of actomyosins. Similar relationships were obtained between environmental temperature and thermodynamic activation parameters for both natural and desensitized actomyosins from which tropomyosin and troponins had been removed. Instead, evidence is presented that the mechanism of temperature adaptation over evolutionary time periods involves selective modifications in the structure of both the heavy and light chains of myosin.     

荒漠蜥蜴的温度适应策略

荒漠蜥蜴是典型的陆生爬行动物,能够通过行为和生理的方式将体温维持在相当狭窄的范围内,以满足其生理活动的需要。在体温调节上,荒漠蜥蜴代表了一种过渡类型,一方面具有变温动物的行为性体温调节特点,同时也产生了哺乳类和鸟类的一些生理性体温调节的雏型。重点介绍荒漠蜥蜴在行为和生理上对温度的适应策略。