Hypothermie | EPFL Graph Search

L'hypothermie est une situation accidentelle et anormale où la baisse de la température centrale d'un animal homéotherme (« à sang chaud ») ne permet plus d'assurer correctement les fonctions vitales. Pour l'hypothermie physiologique et normale, voir : Définitions L'humain, comme les mammifères et les oiseaux, est un homéotherme endotherme, c'est-à-dire qu'il maintient une température généralement supérieure à celle de son milieu, en produisant lui-même une chaleur (thermogénèse). Cette production consomme de l'énergie obtenue à partir de son propre métabolisme. Chez l'humain, la température interne normale est de . Elle est réglable entre certaines limites, et cette thermorégulation est une des fonctions permettant d'assurer le bon déroulement des réactions chimiques et biologiques nécessaires à la vie (homéostasie). On parle d'hypothermie lorsque la température centrale est inférieure à :

de : normothermie ;
de : hypothermie légère ;
de : hypothermie mod

Reduced glutamine concentration improves protein production in growth-arrested CHO-DG44 and HEK-293E cells

Lucia Baldi Unser, David Hacker, Divor Kiseljak, Yashas Rajendra, Florian Maria Wurm

For most cultivated mammalian cells, glutamine is an essential medium component. However, glutamine consumption results in the production of ammonia, a cytotoxic byproduct. Here we investigated the effect of glutamine reduction on recombinant protein production and ammonia accumulation in transiently transfected CHO and HEK-293E cells maintained under conditions of growth arrest. Maximum transient recombinant protein yields were observed in HEK-293E cultures without glutamine and in CHO cultures with 2 mM glutamine. The initial concentration of glutamine correlated with the level of ammonia accumulation in each culture. For both a stable CHO-derived cell line and a polyclonal population of recombinant CHO cells grown under conditions of mild hypothermia, the highest volumetric protein productivity was observed in cultures without glutamine. Here, the level of ammonia accumulation also corresponded to the initial glutamine concentration. Our data demonstrate that reduction of glutamine in the medium is an effective approach to improve protein production in both transiently and stably transfected mammalian cells when applying conditions that reduce or arrest the growth of these cells.

Springer Netherlands2012

Deep hypothermia and rewarming alters glutamate levels and glycogen content in cultured astrocytes

Pierre Magistretti, Luc Pellerin

BACKGROUND: Deep hypothermia has been associated with an increased incidence of postoperative neurologic dysfunction after cardiac surgery in children. Recent studies suggest an excitotoxic mechanism involving overstimulation of glutamate receptors. Extracellular glutamate uptake occurs primarily by astrocytes. Astrocytes also store glycogen, which may be used to sustain the energy-consuming glutamate uptake. Extracellular glutamate and glycogen content were studied during temperature changes mimicking cardiopulmonary bypass in vivo. METHODS: Primary cultures of cerebral cortical astrocytes were used in a specially designed incubator allowing continuous changes of temperature and ambient gas concentrations. The sequence of events was as follows: normothermia, rapid cooling (2.8 degrees C/min) followed by 60 min of deep hypothermia (15 degrees C), followed by rewarming (3.0 degrees C/min) and subsequent 5 h of mild hyperthermia (38.5 degrees C). Two different conditions of oxygenation were studied: (1) normoxia (25% O2, 70% N2, 5% CO2); or (2) hyperoxia (95% O2, 5% CO2). The extracellular glutamate concentrations and intracellular glycogen levels were measured at nine time points. RESULTS: One hundred sixty-two cultures were studied in four independent experiments. The extracellular concentration of glutamate in the normoxic group increased significantly from 35+/-10 nM/mg protein at baseline up to 100+/-15 nM/mg protein at the end of 5 h of mild hyperthermia (P < 0.05). In contrast, extracellular glutamate levels did not vary from control in the hyperoxic group. Glycogen levels decreased significantly from 260+/-85 nM/mg protein at baseline to < 25+/-5 nM/mg protein at the end of 5 h in the normoxic group (P < 0.05) but returned to control levels after rewarming in the hyperoxic group. No morphologic changes were observed in either group. CONCLUSION: The extracellular concentration of glutamate increases, whereas the intracellular glycogen content decreases when astrocytes are exposed to a sequence of deep hypothermia and rewarming. This effect of hypothermia is prevented when astrocytes are exposed to hyperoxic conditions.

1999

Deep hypothermia and rewarming alters glutamate levels and glycogen content in cultured astrocytes

Pierre Magistretti, Luc Pellerin

1999