Non-shivering thermogenesis in common spiny mice Acomys cahirinus from adjacent habitats: response to seasonal acclimatization and salinity acclimation

1. We compared resting metabolic rate (RMR) and non-shivering thermogenesis (NST) values between founder and F1-populations of winter-acclimatized Acomys cahirinus that originated from north- and south-facing slopes (NFS and SFS) of the same valley, representing mesic and xeric habitats. 2. NST was measured by the increase in oxygen consumption (VO2) and body temperature (T-b) after a noradrenaline (NA) injection (VO2 NA, TbNA). 3. Body mass and TbNA values were higher in SFS F1-mice, while RMR and VO2 NA values were higher in NFS F1-mice. Differences were not apparent in founders. 4. Results are consistent with NFS and SFS mice being considered as

Effect of pH and temperature on the formation of volatile compounds in cysteine/reducing sugar/starch mixtures during extrusion cooking

Mixtures of cysteine, reducing sugar (xylose or glucose), and starch were extrusion cooked using feed pH values of 5.5, 6.5, and 7.5 and target die temperatures of 120, 150, and 180 degreesC. Volatile compounds were isolated by headspace trapping onto Tenax and analyzed by gas chromatography-mass spectrometry. Eighty and 38 compounds, respectively, were identified from extrudates prepared using glucose and xylose. Amounts of most compounds increased with temperature and pH. Aliphatic sulfur compounds, thiophenes, pyrazines, and thiazoles were the most abundant chemical classes for the glucose samples, whereas for xylose extrudates highest levels were obtained for non-sulfur-containing furans, thiophenes, sulfur-containing furans, and pyrazines. 2-Furanmethanethiol and 2-methyl-3-furanthiol were present in extrudates prepared using both sugars, but levels were higher in xylose samples. The profiles of reaction products were different from those obtained from aqueous or reduced-moisture systems based on cysteine and either glucose or ribose.

Dynamics of the Indonesian seas circulation. Part I – The influence of bottom topography on temperature and salinity distributions

The influence of bottom topography on the distribution of temperature and salinity in the Indonesian seas region has been studied with a high-resolution model based on the Princeton Ocean Model. One of the distinctive properties of the model is an adequate reproduction of all major topographic features in the region by the model bottom relief. The three major routes of flow of Pacific water through the region have been identified. The western route follows the flow of North Pacific Water through the Sulawesi Sea, Makassar Strait, Flores Sea, and Banda Sea. This is the main branch of the Indonesian Throughflow. The eastern routes follow the flow of South Pacific water through the eastern Indonesian seas. This water enters the region either through the Halmahera Sea or by flowing to the north around Halmahera Island into the Morotai Basin and then into the Maluku Sea. A deep southward flow of South Pacific Water fills the Seram Sea below 1200 m through the Lifamatola Passage. As it enters the Seram Sea, this overflow turns eastward at depths greater than 2000 m, then upwells in the eastern part of the Seram Sea before returning westward at ~1500-2000 m. The flow continues westward across the Seram Sea, spreading to greater depths before entering the Banda Sea at the Buru-Mangole passage. It is this water that shapes the temperature and salinity of the deep Banda Sea. Topographic elevations break the Indonesian seas region down into separate basins. The difference in the distributions of potential temperature, ?, and salinity, S, in adjacent basins is primarily due to specific properties of advection of ? and S across a topographic rise. By and large, the topographic rise blocks deep flow between basins whereas water shallower than the depth of the rise is free to flow between basins. To understand this process, the structure of simulated fields of temperature and salinity has been analyzed. To identify a range of advected ? or S, special sections over the sills with isotherms or isohalines and isotachs of normal velocity have been considered. Following this approach the impact of various topographic rises on the distribution of ? and S has been identified. There are no substantial structural changes of potential temperature and salinity distributions between seasons, though values of some parameters of temperature and salinity distributions, e.g., magnitudes of maxima and minima, can change. It is shown that the main structure of the observed distributions of temperature and salinity is satisfactorily reproduced by the model throughout the entire domain.

High-affinity NO(3-)-H+ cotransport in the fungus Neurospora:induction and control by pH and membrane voltage

High-affinity nitrate transport was examined in intact hyphae of Neurospora crassa using electrophysiological recordings to characterize the response of the plasma membrane to NO3- challenge and to quantify transport activity. The NO3(-)-associated membrane current was determined using a three electrode voltage clamp to bring membrane voltage under experimental control and to compensate for current dissipation along the longitudinal cell axis. Nitrate transport was evident in hyphae transferred to NO3(-)-free, N-limited medium for 15 hr, and in hyphae grown in the absence of a nitrogen source after a single 2-min exposure to 100 microM NO3-. In the latter, induction showed a latency of 40-80 min and rose in scalar fashion with full transport activity measurable approx. 100 min after first exposure to NO3-; it was marked by the appearance of a pronounced sensitivity of membrane voltage to extracellular NO3- additions which, after induction, resulted in reversible membrane depolarizations of (+)54-85 mV in the presence of 50 microM NO3-; and it was suppressed when NH4+ was present during the first, inductive exposure to NO3-. Voltage clamp measurements carried out immediately before and following NO3- additions showed that the NO3(-)-evoked depolarizations were the consequence of an inward-directed current that appeared in parallel with the depolarizations across the entire range of accessible voltages (-400 to +100 mV). Measurements of NO3- uptake using NO3(-)-selective macroelectrodes indicated a charge stoichiometry for NO3- transport of 1(+):1(NO3-) with common K(m) and Jmax values around 25 microM and 75 pmol NO3- cm-2sec-1, respectively, and combined measurements of pHo and [NO3-]o showed a net uptake of approx. 1 H+ with each NO3- anion. Analysis of the NO3- current demonstrated a pronounced voltage sensitivity within the normal physiological range between -300 and -100 mV as well as interactions between the kinetic parameters of membrane voltage, pHo and [NO3-]o. Increasing the bathing pH from 5.5 to 8.0 reduced the current and the associated membrane depolarizations 2- to 4-fold. At a constant pHo of 6.1, driving the membrane voltage from -350 to -150 mV resulted in an approx. 3-fold reduction in the maximum current and a 5-fold rise in the apparent affinity for NO3-. By contrast, the same depolarization effected an approx. 20% fall in the K(m) for transport as a function in [H+]o. These, and additional results are consistent with a charge-coupling stoichiometry of 2(H+) per NO3- anion transported across the membrane, and implicate a carrier cycle in which NO3- binding is kinetically adjacent to the rate-limiting step of membrane charge transit. The data concur with previous studies demonstrating a pronounced voltage-dependence to high-affinity NO3- transport system in Arabidopsis, and underline the importance of voltage as a kinetic factor controlling NO3- transport; finally, they distinguish metabolite repression of NO3- transport induction from its sensitivity to metabolic blockade and competition with the uptake of other substrates that draw on membrane voltage as a kinetic substrate.

NO3- transport across the plasma membrane of Arabidopsis thaliana root hairs:Kinetic control by pH and membrane voltage

High-affinity nitrate transport was examined in intact root hair cells of Arabidopsis thaliana using electrophysiological recordings to characterise the response of the plasma membrane to NO₃^-challenge and to quantify transport activity. The NO₃^--associated membrane current was determined using a three-electrode voltage clamp to bring membrane voltage under experimental control and to compensate for current dissipation along the longitudinal cell axis. Nitrate transport was evident in the roots of seedlings grown in the absence of a nitrogen source, but only 4-6 days postgermination. In 6-day-old seedlings, additions of 5-100 μm NO₃^-to the bathing medium resulted in membrane depolarizations of 8-43 mV, and membrane voltage (V_m) recovered on washing NO₃^-from the bath. Voltage clamp measurements carried out immediately before and following NO₃^-additions showed that the NO₃^--evoked depolarizations were the consequence of an inward-directed current that appeared across the entire range of accessible voltages (-300 to +50 mV). Both membrane depolarizations and NO₃^--evoked currents recorded at the free-running voltage displayed quasi-Michaelian kinetics, with apparent values for K_m of 23 ± 6 and 44 ± 11 μm, respectively and, for the current, a maximum of 5.1 ± 0.9 μA cm^-2. The NO₃^-current showed a pronounced voltage sensitivity within the normal physiological range between -250 and -100 mV, as could be demonstrated under voltage clamp, and increasing the bathing pH from 6.1 to 7.4-8.0 reduced the current and the associated membrane depolarizations 3- to 8-fold. Analyses showed a well-defined interaction between the kinetic variables of membrane voltage, pH_o and [NO₃^-]_o. At a constant pH_o of 6.1, depolarization from -250 to -150 mV resulted in an approximate 3-fold reduction in the maximum current but a 10% rise in the apparent affinity for NO₃^-. By contrast, the same depolarization effected an approximate 20% fall in the K_m for transport as a function in [H⁺]_o. These, and additional characteristics of the transport current implicate a carrier cycle in which NO₃^-binding is kinetically isolated from the rate-limiting step of membrane charge transit, and they indicate a charge-coupling stoichiometry of 2(H⁺) per NO₃^-anion transported across the membrane. The results concur with previous studies showing a high-affinity NO₃^-transport system in Arabidopsis that is inducible following a period of nitrogen-limiting growth, but they underline the importance of voltage as a kinetic factor controlling NO₃^-transport at the plant plasma membrane. © 1995 Springer-Verlag New York Inc.