Role of endogenous cyclo(His-Pro) in cold-induced hypothermia in the desert rat (Mastomys natalensis)

Central administration of exogenous cyclo(His-Pro) (CHP) is known to produce hypothermia in rodents. In the present study, we examined the role of endogenous CHP in cold-induced hypothermia in the desert rat, Mastomys natalensis. The results of these studies show that a rise in hypothalamic CHP content accompanied a decrease in rectal temperature during cold exposure. Immunoneutralization of endogenous CHP resulted in a significant decline in cold-induced hypothermia. In addition, central administration of cyclo(Ala-Gly), a structural analogue of CHP, also led to a decrease in cold-induced hypothermia. The results of these studies show that changes in endogenous CHP levels may affect body temperature regulation.     

Hypothermia induction and recovery in free-ranging rats

1.

To avoid anesthesia confounders, free-ranging rats were exposed (4 h) to cool water (CW; 10 °C; 5 cm), warm water (WW; 35 °C; 5 cm) or temperate air (TA; 25 °C) to induce hypothermia, or control for water or novel environment stress, respectively.     

Enhanced biosorption of mercury(II) and cadmium(II) by cold-induced hydrophobic exobiopolymer secreted from the psychrotroph <Emphasis Type="Italic">Pseudomonas fluorescens</Emphasis> BM07

The cells of psychrotrophic Pseudomonas fluorescens BM07 were found to secrete large amounts of exobiopolymer (EBP) composed of mainly hydrophobic (water insoluble) polypeptide(s) (as contain approximately 50 mol% hydrophobic amino acids, lacking cysteine residue) when grown on fructose containing limited M1 medium at the temperatures as low as 0-10 degrees C but trace amount at high (30 degrees C, optimum growth) temperature. Two types of nonliving BM07 cells (i.e., cells grown at 30 degrees C and 10 degrees C) as well as the freeze-dried EBP were compared for biosorption of mercury (Hg(II)) and cadmium (Cd(II)). The optimum adsorption pH was found 7 for Hg(II) but 6 for Cd(II), irrespective of the type of biomass. Equilibrium adsorption data well fitted the Langmuir adsorption model. The maximum adsorption (Q (max)) was 72.3, 97.4, and 286.2 mg Hg(II)/g dry biomass and 18.9, 27.0, and 61.5 mg Cd(II)/g dry biomass for cells grown at 30 degrees C and 10 degrees C and EBP, respectively, indicating major contribution of heavy metal adsorption by cold-induced EBP. Mercury(II) binding induced a significant shift of infrared (IR) amide I and II absorption of EBP whereas cadmium(II) binding showed only a very little shift. These IR shifts demonstrate that mercury(II) and cadmium(II) might have different binding sites in EBP, which was supported by X-ray diffraction and differential scanning calorimetric analysis and sorption results of chemically modified biomasses. This study implies that the psychrotrophs like BM07 strain may play an important role in the bioremediation of heavy metals in the temperate regions especially in the inactive cold season.     

Conifer seedling distribution and survival in an alpine-treeline ecotone

The importance of seedling establishment to the position ofalpine-treeline is recognized, yet little is known about factorsaffecting the survival of seedlings of treeline conifers during their initialyears of growth and establishment. This establishment period may have thegreatest mortality of all life stages until death of mature trees by disease orfire. Spatial and temporal patterns in the distribution and survival ofseedlings of Picea engelmannii and Abieslasiocarpa were evaluated over four years in analpine-treeline ecotone of the Snowy Range, Wyoming, USA. Seedlings andsaplings of both species occurred most frequently near islands of adult trees.For P. englemannii, this appeared partly due to decreasedsurvivorship of young seedlings (< 5 cm height) with greaterdistance away from tree islands. Survival of emergents of P.engelmannii was 28% greater on the north compared to southsides of tree islands, 48% lower on south-facing slopes comparedto other aspects, and 70% greater with overhead cover such as treebranches. Survival of emergents was greater in microsites with grass cover(90% survival) compared to without ground cover (44% survival),but lowest in microsites surrounded, but not covered, by grass (19%).From 1994–1999, natural seedling emergence and survival washighest in 1995 (80% survival of 221 P.engelmannii,and 100% of seven A. lasiocarpa, in a sample areaof432 m²), when the smallest mean difference in dailymaximum and minimum temperatures occurred, and lowest in 1994 (30% ofseven P. engelmannii), when above-averagetemperatures were accompanied by low rainfall and clear skies. The growthseasons of 1994 and 1995 had among the lowest and highest precipitation of theprevious 30-year period, respectively. In an artificial seedingexperiment, less than 20% of seedlings of both species survived theirfirst complete year of growth. In the autumn of the second year, almost25% additional mortality was observed in the remaining experimentalseedlings when they were exposed to clear, cold skies without the normalprotection of snowcover. Both spatial and temporal patterns of seedlingsurvivalsuggest that exposure to high sunlight may exacerbate low-temperatureandwater stress in young conifer seedlings, inhibiting their establishment in thisalpine treeline.     

Enhanced cold tolerance in transgenic tobacco expressing a chloroplast ω-3 fatty acid desaturase gene under the control of a cold-inducible promoter

A new cold-inducible genetic construct was cloned using a chloroplast-specific omega-3-fatty acid desaturase gene (FAD7) under the control of a cold-inducible promoter (cor15a) from Arabidopsis thaliana. RT-PCR confirmed a marked increase in FAD7 expression, in young Nicotiana tabacum (cv. Havana) plants harboring cor15a–FAD7, after a short-term exposure to cold. When young, cold-induced tobacco seedlings were exposed to low-temperature (0.5, 2 or 3.5°C) for up to 44 days, survival within independent cor15a–FAD7 transgenic lines (40.2–96%) was far superior to the wild type (6.7–10.2%). In addition, the major trienoic fatty acid species remained stable in cold-induced cor15a–FAD7 N. tabacum plants under prolonged cold storage while the levels of hexadecatrienoic acid (16:3) and octadecatrienoic acid (18:3) declined in wild type plants under the same conditions (79 and 20.7% respectively). Electron microscopy showed that chloroplast membrane ultrastructure in cor15a–FAD7 transgenic plants was unaffected by prolonged exposure to cold temperatures. In contrast, wild type plants experienced a loss of granal stacking and disorganization of the thylakoid membrane under the same conditions. Changes in membrane integrity coincided with a precipitous decline in leaf chlorophyll concentration and low survival rates in wild type plants. Cold-induced double transgenic N. alata (cv. Domino Mix) plants, harboring both the cor15a–FAD7 cold-tolerance gene and a cor15a–IPT dark-tolerance gene, exhibited dramatically higher survival rates (89–90%) than wild type plants (2%) under prolonged cold storage under dark conditions (2°C for 50 days).     

Cold-induced vasodilation and vasoconstriction in the finger of tropical and temperate indigenes

While heat acclimatization reflects the development of heat tolerance, it may weaken an ability to tolerate cold. The purpose of this study was to explore cold-induced vasodilation (CIVD) responses in the finger of tropical indigenes during finger cold immersion, along with temperate indigenes. Thirteen tropical male indigenes (subjects born and raised in the tropics) and 11 temperate male indigenes (subjects born and raised in Japan and China) participated. Subjects immersed their middle finger at 4.3±0.8 °C water for 30 min. Rectal temperature, skin temperatures, finger skin blood flow, blood pressure and subjective sensations were recorded during the test. The results showed that: (1) the tropical group demonstrated a lower minimum (T_min), maximum (T_max) and mean finger temperature (T_mean) compared to those of the temperate group (P<0.05); (2) seven tropical indigenes demonstrated a late-plateau type of CIVD pattern, which is characterized by a pronounced 1st vasoconstriction and a single CIVD with a faint and weak 2nd vasoconstriction, whereas no temperate indigene demonstrated the late-plateau type; and (3) the hand temperature at the end of finger immersion was 3 °C lower in the tropical than the temperate group (P<0.05). These results indicate that tropical indigenes have less active responses of arterio-venous anastomoses in the finger and weaker vasoconstrictions after the first CIVD response during finger cold immersion, which can be considered as being more vulnerable to cold injury of the periphery in severe cold.     

Little evidence for a major role of Ca2+ in cold-induced injury of liver cells

We have previously shown that cold-induced injury to hepatocytes and liver endothelial cells occurs predominantly via an iron-dependent pathway. However, other groups have reported evidences suggesting that Ca²⁺ ions could be involved in the process of cold-induced injury of liver cells. We here assessed the relative importance and potential interaction of both pathways in cultured primary hepatocytes and cultured liver endothelial cells. The sequence cold incubation/rewarming of hepatocytes and endothelial cells led to an increase in the cytosolic calcium concentration during the early rewarming phase, but the increased cytosolic calcium concentration did not correlate with cell injury. A partial protection from cold-induced cell injury was achieved by the intracellular calcium chelators Quin-2 and BAPTA. However, additional experiments showed that the ability of these chelators to bind iron was probably responsible for a major part of this protection. Incubation in calcium-free media led to an increased cell injury and a physiological calcium concentration (2.5 mM) was protective. In addition, targeting suggested downstream pathways of calcium-dependent cold-induced injury, i.e. by the addition of Ruthenium Red, an inhibitor of mitochondrial Ca²⁺ uniporter, or by inhibiting Bax translocation to the mitochondria, did not provide protection from cold-induced injury in both cell types. Taken together, our data suggest that calcium increases but does not play a major role in cold-induced cell injury to hepatocytes and liver endothelial cells.     

Iron-dependent vs. iron-independent cold-induced injury to cultured rat hepatocytes: a comparative study in physiological media and organ preservation solutions

We previously described the entity of cold-induced apoptosis to rat hepatocytes and characterized its major, iron-dependent pathway. However, after cold incubation in some solutions, e.g. cell culture medium, hepatocytes show an additional, yet uncharacterized component of cold-induced injury. We here assessed the effects of organ preservation solutions on both components of cold-induced injury and tried to further characterize the iron-independent component. None of the preservation solutions (University of Wisconsin, histidine-tryptophan-ketoglutarate, Euro-Collins, histidine-lactobionate, sodium-lactobionate-sucrose and Celsior solutions) provided significant protection against cold-induced cell injury (LDH release after 24-h cold incubation/3h rewarming >65% for all solutions); three solutions even enhanced cold-induced injury. However, when the predominant iron-dependent mechanism was eliminated by the addition of iron chelators, all preservation solutions yielded hepatocyte protection that was clearly superior to the one obtainable in cell culture medium or Krebs-Henseleit buffer with iron chelators (LDH release after 24-h cold incubation/3h rewarming 相似文献