Ammonia nitrogen and inorganic phosphorus excretion by the planktonic rotifers

Two series of experiments were carried out to determine the relation of the rate of phosphorus and nitrogen excretion by the planktonic rotifers to ambient temperature and individual body weights of these animals. The following formulas describing this relation were obtained: E_P=0.0154 W^?1.27 e^0.096T E_N=0.0879 W^?1.01 e^{0.088 T}, where E_P and E_N denote the rate of P and N excretion, respectively, in µg · mg dry wt^?1 · h^?1, W is body weight in µg dry weight, and T is temperature in °C.     

A new model system for studying the phosphatidylinositol cycle

An early manifestation of the response of WRK-1 rat mammary tumor cells to vasopressin is an increase in incorporation of (³²P)P_i into phospholipids. Incorporation into all classes of phospholipids is stimulated; however, incorporation into phosphatidylinositol (PI) is increased to the greatest degree (3- to 10-fold as compared with 1.3- to 2-fold for the other phosholipids). Furthermore, increased incorporation into PI is accompanied by an increased rate of PI turnover; turnover rates of the other phospholipids are unaffected by vasopressin.     

EVIDENCE FOR INVOLVEMENT OF Ca2+ IN THE INCORPORATION OF 32Pi INTO THE PHOSPHATIDYLINOSITOL OF RAT DIAPHRAGM

Abstract— Ethyleneglycol-bis (β-aminoethyl ether)-N-N'-tetraacetic acid (EGTA) inhibited the incorporation of ³²P_i into phosphatidylinositol (PI) in rat diaphragm incubated in Ca²⁺-free Krebs-Ringer medium. Only the labelling of the PI was altered, and no effects on the pool size of PI or on the incorporation of ³²P_i into other phospholipids were observed. The effect of EGTA was concentration-dependent and appeared to be related to its Ca^a+-chelating properties; the inhibition of the incorporation of ³²P_i could be completely reversed by the addition of excess Ca²⁺ but not Mg²⁺. The inhibitory effect of the EGTA was progressively enhanced by lengthening the preincubation of the tissue with EGTA, an observation suggesting that chelation of intracellular or membrane-bound Ca²⁺, rather than extracellular Ca²⁺, was involved in the effect. In contrast to its inhibition of the incorporation of ³²P_i EGTA enhanced the incorporation of [³H]inositol into PI, but this effect was accompanied by an appreciable increase in total uptake of [³Hlinositol by the tissue. Our results suggest that the level of intracellular Ca²⁺ plays a role in the regulation of the incorporation of ³²P_i into PI. Addition of unlabelled α-glycerophosphate to the incubation medium of tissues which had been preincubated with 2-deoxy-d -glucose failed to cause a significant diminution in the inhibition by EGTA of the incorporation of ³²P_i into PI. This experiment suggests, but does not prove, that the effect of EGTA was not at the level of incorporation of ³²P_i into α-glycerophosphate.     

The effect of cold-induced increased metabolic rate on the rate of <Superscript>13</Superscript>C and <Superscript>15</Superscript>N incorporation in house sparrows (<Emphasis Type="Italic">Passer domesticus</Emphasis>)

Animals with high metabolic rates are believed to have high rates of carbon and nitrogen isotopic incorporation. We hypothesized that (1) chronic exposure to cold, and hence an increase in metabolic rate, would increase the rate of isotopic incorporation of both ¹³C and ¹⁵N into red blood cells; and (2) that the rate of isotopic incorporation into red blood cells would be allometrically related to body mass. Two groups of sparrows were chronically exposed to either 5 or 22°C and switched from a ¹³C-depleted C₃-plant diet to a more ¹³C-enriched C₄-plant one. We used respirometry to estimate the resting metabolic rate of birds exposed chronically to our two experimental temperatures. The allometric relationship between the rate of ¹³C incorporation into blood and body mass was determined from published data. The of birds at 5°C was 1.9 times higher than that of birds at 22°C. Chronic exposure to a low temperature did not have an effect on the rate of isotopic incorporation of ¹⁵N save for a very small effect on the incorporation of ¹³C. The isotopic incorporation rate of ¹³C was 1.5 times faster than that of ¹⁵N. The fractional rate of ¹³C incorporation into avian blood was allometrically related to body mass with an exponent similar to −1/4. We conclude that the relationship between metabolic rate and the rate of isotopic incorporation into an animal’s tissues is indirect. It is probably mediated by protein turnover and thus more complex than previous studies have assumed.     

Synthesis and polymorphic phase behaviour of polyunsaturated phosphatidylcholines and phosphatidylethanolamines

A series of phosphatidylcholines and phosphatidylethanolamines was synthesized containing two acyl chains of the following polyunsaturated fatty acids: linoleic acid (18:2), linolenic acid (18:3), arachidonic acid (20:4) and docosahexaenoic acid (22:6). In addition two phospholipids with mixed acid composition were synthesized: 16:0/18:1_c phosphatidylcholine and 16:0/18:1_c phosphatidylethanolamine. The structural properties of these lipids in aqueous dispersions in the absence and in the presence of equimolar cholesterol were studied using ³¹P-NMR, freeze fracturing and differential scanning calorimetry (DSC).The phosphatidylcholines adopt a bilayer configuration above 0°C. Incorporation of 50 mol% of cholesterol in polyunsaturated species induces a transition at elevated temperatures into structures with ³¹P-NMR characteristics typical of non-bilayer organizations. When the acyl chains contain three or more double bonds, this non-bilayer organization is most likely the hexagonal H_II phase, 16:0/15:1_c phosphatidylethanolamine shows a bilayer to hexagonal transition temperature of 75°C. The polyunsaturated phosphatidylethanolamines exhibit a bilayer to hexagonal transition temperature below 0°C which decreases with increasing unsaturation and which is lowered by approximately 10°C upon incorporation of 50 mol% of cholesterol. Finally, it was found that small amounts of polyunsaturated fatty acyl chains in a phosphatidylethanolamine disproportionally lower its bilayer to hexagonal transition temperature.     

Involvement of periodic deacylation-acylation cycles of mitochondrial phospholipids during Sr2+-induced oscillatory ion transport in rat liver mitochondria

Lysophosphatidylcholine and lysophosphatidylethanolamine levels were determined during Sr²⁺-induced oscillating ion fluxes in mitochondria prelabelled in vivo with ³²P_i. Periodic fluctuations of both lyso compounds were established with an increase at the stage of simultaneously monitored K⁺ influx and a decrease at K⁺ efflux. The periodic activations and inactivations of phospholipase were found to be associated with periodic changes in the incorporation rates of labelled polyunsaturated fatty acids with an apparent phase difference of 180°. Periodic deacylation-acylation cycles of phospholipids accompanying the periodic cycles of reversible ion accumulation and release are suggested to be involved in the trigger mechanism generating the permeability changes during oscillatory ion transport.     

Unsaturated fatty acid synthesis in sunflower (Helianthus annuus L.) seeds in response to night temperature

The incorporation of ¹⁴CO₂ into unsaturated fatty acids during seed development was measured in sunflowers grown in controlled environments with day temperatures of 28°C and night temperatures of 15°C or 22°C. While the average temperatures to which the plants were exposed did not differ greatly, the ratio of linoleic acid to oleic acid synthesized was much greater at a night temperature of 15°C than at 22°C. These results support the proposal (Harris et al. 1978) that the mean minimum temperature experienced during seed development is the major environmental factor influencing the unsaturated fatty acid composition of sunflower seed oil.     

Effects of microwave exposure and temperature on survival of mice infected with Streptococcus pneumoniae

Female CD-1 mice were injected with an LD₅₀ dose of Streptococcus pneumoniae and then exposed to 2.45 GHz (CW) microwave radiation at an incident power density of 10 mW/cm² (SAR = 6.8 W/kg), 4 h/d for 5 d at ambient temperatures of 19 °C, 22 °C, 25 °C, 28 °C, 31 °C, 34 °C, 37 °C and 40 °C. Four groups of 25 animals were exposed at each temperature with an equal number of animals concurrently sham-exposed. Survival was observed for a 10-d period after infection. Survival of the sham-exposed animals increased as ambient temperature increased from 19 °C–34 °C. At ambient temperatures at or above 37 °C the heat induced in the body exceeded the thermoregulatory capacity of the animals and deaths from hyperthermia occurred. Survival of the microwave-exposed animals was significantly greater than the shams (～20%) at each ambient temperature below 34 °C. Based on an analysis of the data it appears that the hyperthermia induced by microwave exposure may be more effective in increasing survival in infected mice than hyperthermia produced by conventional methods (ie, high ambient temperature). Microwave radiation may be beneficial to infected animals at low and moderate ambient temperatures, but it is detrimental when combined with high ambient temperatures.     

Energy-dependent uptake of ochratoxin A by mitochondria.

The interaction of ochratoxin A, a mycotoxin produced by Aspergillus ochraceus, with isolated rat liver mitochondria and plasma membranes has been studied. Cell membranes bind [¹⁴C]ochratoxin A poorly and do not show saturation in the concentration range examined. The uptake of the toxin by mitochondria is saturable, with an apparent K_m at 0 °C of 30 nmol/mg of protein. Sonication or freeze-thawing reduces the extent of incorporation by 88%. Ochratoxin A uptake is energy dependent, resulting in a depletion of intramitochondrial ATP. Uncouplers such as m-chlorocarbonylcyanide phenylhydrazone or the respiratory inhibitors rotenone and antimycin A inhibit uptake 60–85%, while ATP reverses the antimycin and rotenone inhibition. Phosphate transport is sensitive to inhibition by the toxin, as measured by Ca²⁺ plus P_istimulated respiration and [³²P]P_i incorporation. In turn, phosphate inhibits nearly completely [¹⁴C]ochratoxin A uptake at 22 °C and causes a concomitant mitochondrial swelling yet is not incorporated into the matrix space. Thus, the saturable uptake of ochratoxin A is accompanied by a decrease in the energy state and inhibition of P_i transport, which results in deteriorative changes of the mitochondria, as evidenced by large-amplitude swelling.     

Thermolabile Liposomes with a High Fusion Efficacy at 42°C can be Made of Dipalmitoylphosphatidylcholine/Fatty Alcohol Mixtures in the Molar Ratio of 1/2

Abstract

Liposomes made of dipalmitoylphosphatidylcholine (DPPC²), dipalmitoyl-phosphatidylglycerol (DPPG), and different long-chain fatty alcohols were investigated with respect to their colloidal stability, chain-melting phase transition temperature, and temperature dependent inter-vesicle fusion. In particular, the practical usefulness of the stoichiometric 1/2 (mol/mol) mixtures of the phospholipids and fatty alcohols, mainly elaidoyl alcohol (EL-OH) were studied. The mole fraction of DPPG in the bilayers of such vesicles affects crucially the colloidal stability of the resulting lipid suspensions; at least 15 mol-% of DPPG (relative to DPPC) must be incorporated into the bilayers in order to make the liposome suspension colloidally sufficiently stable at room temperature. The corresponding DPPC/DPPG/EL-OH (0.85/0.15/2) mixed lipid vesicles undergo a lamellar-gel to inverted hexagonal (H_IT) phase transition at 52.7°C, however, and then fuse and aggregate massively. The related phase transition temperature of the DPPC/DPPG/palmitelaidoyl alcohol (0.85/0.15/2) mixture is 48.4°C. This indicates that the chain-melting phase transition temperature of the investigated lipid mixtures is rather sensitive to the alcohol chain-length. This transition temperature is independent, however, of the bulk proton concentration in the pH region between 4.9 and 7.2. Stoichiometric 1/2 mixtures of phospholipids and EL-OH have a high propensity for the inter-vesicle fusion at 42°C and neutral pH. The reason for such fusion 10°C below the lamellar-to-nonlamellar phase transition temperature are the defects that are generated during the chain-melting of the (partly segregated) phospholipid component at 42°C; the proximity of the lamellar to non-lamellar phase transition temperature of the phospholipid/fatty alcohol (1/2) complex at 52°C also plays an important role.     

Effects of temperature on L-leucine transport in toadfish liver in vivo

The effect of body temperature in the 4–30°C range on L-leucine uptake by toadfish liver in vivo was examined by means of a single-injection pulse technique. The ratio of [¹⁴C]leucine to [³H]mannitol or [³H]inulin in blood leaving the liver was measured as a function of time after hepatic portal vein injection. Recoveries of the two isotopes in liver and [¹⁴C]leucine incorporation into protein were determined.The Q₁₀ value for influx was 3.8, that for efflux 2.8. At all temperatures, the leucine influx was 8–10-times higher than its incorporation into protein. The directly energy-linked reactions appear to be the main site of increased temperature sensitivity at low temperatures.     

SEASONAL EFFECT ON THE RELATIONSHIP BETWEEN THE PHOTOSYNTHETIC CAPACITY OF INTERTIDAL MICROPHYTOBENTHOS AND TEMPERATURE1

The response of the photosynthetic capacity (P_max) of microphytobenthos to short-term variations of temperature (in the range 5–35° C) was assessed on a seasonal basis. The relationship is described mathematically, and relevant physiological parameters are identified: P_MAX, the maximum value of P_max achieved at T_opl, the optimum temperature. Estimated values of T_opt do not change significantly throughout the year and remain close to 25° C. It is thus concluded that T_opt is not influenced by seasonal variations in the daily range of mud surface temperature. Identical conclusions hold for T_max (ca. 38° C), the thermal threshold beyond which no photosynthesis occurs. Conversely, P_MA estimates exhibit substantial variability: P_MAX (mean ± root mean square error) is highest in April (11.18 ± 0.42 [μg C · [μg Chl a]^?1· h^?1) during the beginning of the annual increase in temperature, photoperiod, and maximum irradiance and is lowest in December (3.04 ± 0.16 μg C · [μg Chl a]^?1· h^?l). From an ecological point of view, the short-term and seasonal variations of P_MAX suggest that the microphytobenthic community takes advantage of the abiotic spring environmental conditions, allowing the onset of the bloom. Nevertheless, no “acclimation strategy” (i.e. shifts in T_opt and T_max that prevent temperature inhibition in summer or improve photosynthetic rates in winter) is apparent from our results.     

Phospholipid metabolism in Mycobacterium smegmatis ATCC 607 grown at 37° C and 27° C

The rate of synthesis and degradation of phospholipids in Mycobacterium smegmatis ATCC 607, grown at 27° C and 37° C was studied by incorporation of ³²P into phospholipids and chase of radioactivity of the pulse-labelled phospholipids. A relatively low rate of synthesis and degradation of phospholipids in cells growth at 27° C was observed as compared to those grown at 37° C. Phosphatidylethanolamine (PE) had the maximum turnover at 37° C. However, at 27° C, cardiolipin (CL) showed a turnover rate higher than PE. Phosphatidylinositol mannosides (PIMs) were metabolically more active at 37° C than at 27° C. The differences in metabolic activity of the phospholipids at the two temperatures have been discussed.     

Estimation of intracellular pH in muscle of fishes from different thermal environments

A technique based on homogenisation of rapidly frozen tissue was used to investigate the regulation of intracellular pH (pH_i) in freshwater and marine fish from diverse environmental temperatures. The following species were held at ambient temperatures of ca. 1°C (Notothenia coriiceps; Antarctica), 5°C (Pleuronectes platessa, Myoxocephalus scorpius; North Sea), and 26°C (Oreochromis niloticus; African lakes). The effects of seasonal acclimatisation to 4, 11 and 18°C were also examined in rainbow trout in the winter, autumn and summer, respectively. Extracellular (whole blood) pH (pH_e) did not follow the constant relative alkalinity relationship, where pH⁺=pOH⁻ for any particular temperature, over a range of 1–26°C (overall δpH_e/δT=0.009±0.002 U °C⁻¹; P<0.001), apparently being regulated by ionic fluxes and ventilation. Intracellular pH (pH_i) was also regulated independently of pN(=0.5 pK water) in all species of fish examined. The inverse relationship between pH_i and environmental temperature gave an overall δpH_i/δT of −0.010±0.001 U °C⁻¹ (for both white and red muscle) and −0.004±0.003 U °C⁻¹ (cardiac muscle). However, between 1 and 11°C δpH_i/δT was much higher (P<0.001), −0.022±0.003 U °C⁻¹ (white muscle) and −0.022±0.004 U °C⁻¹ (red muscle). The possible adaptive roles for these different acid–base responses to environmental temperature variation among tissues and species, and the potential difficulties of estimating pH_i, are discussed.     

Phospholipase A2 Stimulation by Methyl Mercury in Neuron Culture

Abstract: In primary prelabeled cultures of cerebellar granule cells, methyl mercury (MeHg) induced a concentration- and time-dependent release of [³H]arachidonic acid. MeHg-induced [³H]arachidonate release was partially dependent on the extracellular Ca²⁺ concentration. MeHg at 10–20 µM also stimulated basal ⁴⁵Ca²⁺ uptake after 20 min of incubation at 37°C, and at 10 µM inhibited K⁺ depolarization-stimulated uptake. MeHg stimulated [³H]arachidonate uptake, but had no effect on the rate of phospholipid reacylation. Phospholipase A₂ (PLA₂) activation preceded cytotoxicity, but at higher concentrations of MeHg such dissociation was not evident. Inhibition of MeHg-induced PLA₂ activation by 100 µM mepacrine failed to modify cytotoxicity. MeHg-induced lipoperoxidation, measured as the production of thiobarbituric acid-reacting products, was inhibited by α-tocopherol without inhibition of [³H]arachidonate release. The absence of α-tocopherol inhibition of MeHg-induced arachidonate release precludes a causal role for lipoperoxide-induced PLA₂ activation in this system. Moreover, MeHg induced an increased susceptibility of unilamellar vesicles to exogenous PLA₂ in the presence of low Ca²⁺ concentrations without evidence of lipid peroxidation. [³H]Arachidonate incorporation into granule neuron phospholipids was analyzed by isocratic HPLC analysis. Relatively high proportional incorporation was found in the combined phosphatidylcholine fractions and phosphatidylinositol. With MeHg, an increase in the relative specific activity of incorporation was found in the phosphatidylinositol fraction, indicating a preferential turnover in this phospholipid species in the presence of MeHg.     

Rate of metabolism in the smallest simian primate,the pygmy marmoset (Cebuella pygmaea)

Rate of metabolism was measured with six adult pygmy marmosets (Cebuella pygmaea) at regulated ambient temperatures ranging between 20°C and 35°C. A novel combined nest box and metabolic chamber was designed to allow nighttime measurements on immobile animals in their home cage without disturbance. The basal rate of metabolism (BMR) was 98 ml O₂ h⁻¹, representing 74% of the value expected from the equation of McNab [Quarterly Review of Biology 63:25–54, 1988] relative to body mass. The thermoneutral zone was approximately 27–34°C. Below the lower critical temperature (27–28°C), thermal conductance (12.9 ml O₂ h⁻¹ °C⁻¹) was close to the predicted value. Body temperature ranged between 34.9°C and 35.5°C at night. When two animals rested together overnight in the nest box, the lower critical temperature was slightly lowered, and individual energy expenditure at 20–21°C was reduced by about 34%. The basal rate of metabolism of C. pygmaea is much lower than reported in an earlier study based on daytime measurements but agrees with values reported from a more recent study conducted at night with a classical metabolic chamber. In order to compare the BMR of C. pygmaea with that of other primates, 23 species were included in a comparative study taking into account both phylogeny and body mass (independent contrasts approach). The scaling exponent of BMR to body mass obtained was indistinguishable from that published for eutherian mammals in general. Cebuella and Callithrix exhibit the lowest basal rates known for simians. This trait may possibly be linked to the natural diet, which includes a large proportion of gums that are difficult to digest, but additional metabolic studies on primates are needed for further examination of its adaptive significance. Am. J. Primatol. 41:229–245, 1997. © 1997 Wiley-Liss, Inc.     

Fatty acid exchange of phospholipids in membranes of rat heart

Incorporation of ¹⁴C fatty acids in phospholipids of plasma membranes and sarcoplasmic reticulum of rat heart was studied. Mainly phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were labelled. Our studies showed that the incorporation of unsaturated fatty acids (oleic and linoleic acid) was higher than for saturated fatty acids (palmitic and stearic acid). The range of uptake was between 0.2 and 2.2 nmol·mg⁻¹ protein·h⁻¹ and 0.5–7.4 nmol·μgatom⁻¹ P₁·h⁻¹, respectively. Uptake of activity in individual phospholipids (measured after separation on TLC) was calculated as percentage of total activity. Incorporation in phosphatidylcholine was higher than in phosphatidylethanolamine. Phosphatidylcholine showed an increasing sequence for the following fatty acids: C_18:0 < C_16:0 < C_18:0 < C_18:2. However, phosphatidylethanolamine showed a decreasing sequence for the incorporation of the same fatty acids. Labelling of PC was always greater than for PE, except for stearic acid which was better incorporated into phosphatidylethanolamine. Uptake of the same fatty acid into phospholipids of sarcoplasmic reticulum was always higher than uptake into plasma membranes. As incorporation of fatty acids bound to albumin was studied in isolated membranes of rat heart, the addition of ATP and CoASH was an absolute requirement.     

Interaction of [3H]gibberellin A1 with a sub-cellular fraction from lettuce (Lactuca sativa L.) hypocotyls

The relationship between elongation growth and the incorporation of [³H]gibberellin A₁ ([³H]GA₁) into a 2,000g pelletable (2KP) fraction from lettuce (Lactuca sativa L., cv. Arctic) hypocotyl sections has been examined. Sections were loaded with incremental amounts of GA₁ under conditions where growth was arrested (5° C) or permitted (30° C) and, after 16 h, all were transferred to a GA-free medium at 30° C. Growth and 2KP radioactivity were measured at this point and after a further 24 h in the chase medium. Uptake was reduced by 80% at 5° C, as compared to 30° C, but 2KP labelling and protein synthesis were only reduced by half. The growth rate of the 5° C pretreated sections during the chase period was comparable to that observed during the pulse in the 30° C material but the dose/response relationship was flatter. Low temperature sections incorporated a much higher percentage of GA₁ uptake into the 2KP fraction (27% at maximum) but the absolute levels of labelling at this temperature were lower than those measured at 30° C. The data are interpreted as showing that 2KP labelling is not a consequence of growth. It must either precede response or be an unconnected concurrent process.