Sucrose consumption in mice: Major influence of two genetic Loci affecting peripheral sensory responses

Individual variability in sucrose consumption is prominent in humans and other species. To investigate the genetic contribution to this complex behavior, we conducted behavioral, electrophysiological, and genetic studies, using male progeny of two inbred mouse strains (C57BL/6ByJ [B6] and 129/J [129]) and their F₂ hybrids. Two loci on Chromosome (Chr) 4 were responsible for over 50% of the genetic variability in sucrose intake. These loci apparently modulated intake by altering peripheral neural responses to sucrose. One locus affected the response threshold, whereas the other affected the response magnitude. These findings suggest that the majority of difference in sucrose intake between male B6 and 129 mice is due to polymorphisms of two genes that influence receptor or peripheral nervous system activity. Received: 27 January 1997 / Accepted: 17 March 1997     

In situ CO2 gas-exchange in fruits of a tropical tree,Durio zibethinus Murray

We examined the in situ CO₂ gas-exchange of fruits of a tropical tree, Durio zibethinus Murray, growing in an experimental field station of the Universiti Pertanian Malaysia. Day and night dark respiration rates were exponentially related to air temperature. The temperature dependent dark respiration rate showed a clockwise loop as time progressed from morning to night, and the rate was higher in the daytime than at night. The gross photosynthetic rate was estimated by summing the rates of daytime dark respiration and net photosynthesis. Photosynthetic CO₂ refixation, which is defined as the ratio of gross photosynthetic rate to dark respiration rate in the daytime, ranged between 15 and 45%. The photosynthetic CO₂ refixation increased rapidly as the temperature increased in the lower range of air temperature T _c (T _c <28.5 °C), while it decreased gradually as the temperature increased in the higher range (T _c 28.5 °C). Light dependence of photosynthetic CO₂ refixation was approximated by a hyperbolic formula, where light saturation was achieved at 100 mol m^–2 s^–1 and the asymptotic CO₂ refixation was determined to be 37.4%. The estimated gross photosynthesis and dark respiration per day were 1.15 and 4.90 g CO₂ fruit^–1, respectively. Thus the CO₂ refixation reduced the respiration loss per day by 23%. The effect of fruit size on night respiration rate satisfied a power function, where the exponent was larger than unity.     

Methanogenic granular sludge formation in an upflow anaerobic sludge blanket reactir treating synthetic methanolic waste

A laboratory upflow anaerobic sludge blanket reactor, seeded with fine, suspended, bacterial floc with 1.76 g volatile suspended solids/l, was used to treat synthetic methanolic waste. After 180 days of continuous peration, granular sludge with discrete granules of 1 to 2 mm diam. was formed, with 52 g volatile suspended solids/l. Granules were brown, relatively soft and had a settling velocity of 1.61 cm/s. Extracellular polymeric matter extracted from the granular sludge had high carbohydrate content but low nucleic acid content. The ash of the granular sludge contained Na⁺, K⁺ and Mg²⁺ up to 15.0, 11.7 and 3.75 mg/g, respectively. Scanning and transmission electron microscopy revealed that the granular sludge was dominated by methanogens resembling Methanosarcina.The authors are with the Department of Environmental Engineering, Faculty of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565, Japan     

Properties of peroxisomes and their induction by clofibrate in normal adult rat hepatocytes in primary culture

Alterations in peroxisomes and catalase activity and their responsiveness to clofibrate in adult rat hepatocytes in primary culture were investigated. The numbers of peroxisomes with and without crystalloid nucleotids per unit cytoplasmic area were preserved in cultured hepatocytes for 2 d after seeding at a level comparable to that of freshly isolated hepatocytes. At Day 3 in culture, the number of anucleoid peroxisomes was reduced in untreated hepatocytes, accompanied by more significant reduction in the number of nucleoid-containing peroxisomes, which decreased until Day 5. Peroxisome diameters were reduced in untreated hepatocytes at Day 2 and this decrease in the diameter was continued until Day 7. Catalase activity in untreated hepatocytes decreased markedly with culture age. The number of anucleoid peroxisomes was significantly greater in hepatocytes treated with 2 mM clofibrate in culture than in freshly isolated hepatocytes for 2 d or in untreated hepatocytes of the same culture age through 7 d. The number of nucleoid-containing peroxisomes in the treated cells began to decrease in 3 d, but was greater than that of untreated cells at Days 3 and 5. Peroxisomes with well-developed nucleoids were observed frequently in the treated cells even at Day 7. Peroxisome diameters were greater in the treated cells than in untreated cells at Days 3, 5, and 7. Catalase activity was always higher in the treated cells than in untreated cells. These results suggest that clofibrate is effective in inducing peroxisome proliferation as well as in maintaining the organelles in cultured hepatocytes.     

Adenine-nucleotide levels and metabolism-dependent membrane potential in cells of Nitellopsis obtusa Groves

The relationship between adenine-nucleotide levels and metabolism-dependent membrane potential was studied in cells of Nitellopsis obtusa. Effects of ADP and AMP in the presence of ATP on electrogenic pump activity were measured in the dark, using the continuous perfusion method. Both ADP and AMP acte as competitive inhibitors for ATP, the K_i value for either compound being about 0.4 mM. The role of ADP and AMP as regulating factors for the electrogenic pump was investigated under various metabolic conditions. Application of N₂ gas in the dark caused a significant membrane depolarization amounting to 90 mV, but cytoplasmic streaming and membrane excitability were not affected. Under anoxia, the ATP level decreased from 1.6 to 0.5 mM; ADP increased but only slightly, and AMP increased greatly. However, the time course of changes in the adenine nucleotides was not concurrent with that of the membrane-potential changes, thus, the adenine-nucleotide level changes cannot fully account for the N₂-elicited depolarization. Under light, although the membrane hyperpolarized, no significant changes in the adenine-nucleotide levels were observed. Therefore, the light-induced membrane hyperpolarization cannot be explained solely by changes in adenine-nucleotide levels.Abbreviations APW artificial pond water - E_m membrane potential - R_m membrane resistance     

Control of membrane potential and excitability ofChara cells with ATP and Mg2+

Summmary Electric characteristics of internodalChara australis cells, from which the tonoplast had been removed by vacuolar perfusion with media containing EGTA, were studied in relation to intracellular concentrations of ATP and Mg²⁺ using the ordinary microelectrode method and the open-vacuole method developed by Tazawa, Kikuyama and Nakagawa (1975.Plant Cell Physiol. 16:611). The concentration of ATP was decreased by introducing hexokinase and glucose into the cell and that of Mg²⁺ by introducing EDTA or CyDTA. The membrane potential decrease and the membrane resistance increase were both significant when the ATP or Mg²⁺ concentration was decreased. An ATP-dependent membrane potential was also found in other species of Characeae,Nitella axillaris andN. pulchella. Excitability of the membrane was also completely lost by reducing the ATP or Mg²⁺ concentration. Both membrane potential and excitability were recovered by introducing ATP or Mg²⁺ into ATP- or Mg²⁺-depleted cells.The time course of membrane potential recovery was followed by the open-vacuole method. Recovery began as soon as intracellular perfusion with medium containing ATP and Mg²⁺ was started. Reversible transition of the membrane potential between polarized and pepolarized levels by controlling the intracellular concentration of ATP or Mg²⁺ could be repeated many times by the open-vacuole method, when the excitability was suppressed by addition of Pb²⁺ to the external medium.The ineffectiveness of an ATP analog, AMP-PNP, and the synergism of ATP and Mg²⁺ in maintaining the membrane potential and excitability strongly suggest that ATP act via its hydrolysis by Mg²⁺-activated ATPase. The passive nature of the membrane, as judged from responses of the membrane potential to changes of the external K⁺ concentration, was not altered by lowering the ATP concentration in the cell. The mechanism of membrane potential generation dependent on ATP is discussed on the basic of an electrogenic ion pump. Involvement of the membrane potential generated by the ion pump in the action potential is also discussed.     

Roles of cell surface components of Escherichia coli K-12 in bacteriophage T4 infection: interaction of tail core with phospholipids.

The cell surface of Escherichia coli K-12, reconstituted from the OmpC protein, lipopolysaccharide, and the peptidoglycan layer, was active as a receptor for phage T4, resulting in the contraction of the tail sheath and the penetration of the core through the cell surface (Furukawa et al., J. Bacteriol. 140:1071--1080, 1979). In the present work the process of DNA ejection from the contracted T4 phage particle was studied. Contracted phage particles were adsorbed to phospholipid liposomes by the core tip. This adsorption resulted in ejection of phage DNA. Either phosphatidylglycerol or cardiolipin was active for the DNA ejection. A proton motive force across the liposome membrane was not required for these processes. The process of DNA ejection, however, was temperature dependent, whereas the adsorption of the core tip to liposomes took place at 4 degrees C. Based on these observations together with those in the previous paper, the process of T4 infection of E. coli K-12 cells is discussed with special reference to the roles of cell surface components.     

Demonstration of light-induced potential change in Chara cells lacking tonoplast

Chara cells without tonoplasts, prepared by replacing the cellsap with EGTA-containing media, showed essentially the samepattern of light-induced changes in membrane potential and membraneresistance as normal cells although the concentrations of ionsand ATP in the cytoplasm decreased considerably (1/3–1/10)after loss of the tonoplast. Removal of the tonoplast reducedthe rate of photosynthetic O₂ evolution to about 50% of thatof normal cells but did not affect the magnitude of light-inducedpotential change. Not a full but a certain level of electronflow seems necessary to activate the putative electrogenic H⁺-pump. ¹ Present address: Department of Botany, Faculty of Science,University of Tokyo, Japan. ² Present address: Niigata College of Pharmacy, Niigata 950-21,Japan. (Received September 4, 1978; )     

Determination of serum unconjugated estrone, estradiol-17β and estriol during pregnancy by selected ion monitoring

A simple, rapid and highly specific method by selected ion monitoring (SIM), using 9α,11α-[²H₂]estrone, [2,4-²H₂]estradiol-17β and 2,4-[²H₂]estriol as internal standards, was developed for the determination of serum estrogens during pregnancy. Serum samples were submitted to a simple extraction procedure and were analysed after formation of the trifluoroacetic anhydride derivative. The inter-assay coefficients of variation for estrone, estradiol-17β and estriol were 3.73%, 3.42% and 3.49%, respectively. The results obtained by SIM were compared with analysis performed using radioimmunoassay.