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G Dupont

Publications and source records attributed to G Dupont.

At least 55 records · Page 3Linked to original sources
PubMed1990

Allosteric regulation, cooperativity, and biochemical oscillations.

Allosteric regulation is associated with a number of periodic phenomena in biochemical systems. The cooperative nature of such regulatory interactions provides a source of nonlinearity that favors oscillatory behavior. We assess the role of cooperativity in the onset of biochemical oscillations by analyzing two specific examples. First, we consider a model for a product-activated allosteric enzyme which has previously been proposed to account for glycolytic oscillations. While enzyme cooperativity plays an important role in the occurrence of oscillations, we show that these may nevertheless occur in the absence of cooperativity when the reaction product is removed in a Michaelian rather than linear manner. The second model considered was recently proposed to account for signal-induced oscillations of intracellular calcium. This phenomenon originates from a nonlinear process of calcium-induced calcium release. Here also, the cooperative nature of that positive feedback favors the occurrence of oscillations but is not absolutely required for periodic behavior. Besides underlining the importance of cooperativity, the results highlight the role of diffuse nonlinearities distributed over several steps within a regulated system: even in the absence of cooperativity, such mild nonlinearities (e.g., of the Michaelian type) may combine to raise the overall degree of nonlinearity up to the level required for oscillations.

Allosteric Regulation↗
PubMed1990

Comparison of creatinine and inulin clearances in multiple trauma.

Creatinine clearance (Ccr) is a good predictor of renal dysfunction. However, numerous analytical interferences have been observed with the classical measurement of creatinine by Jaffé's procedure. This prospective study was conducted to compare 4 methods for determining creatinine; and also endogenous creatinine clearance with inulin clearance (Cin) to estimate the glomerular filtration rate. The 4 different techniques for measuring creatinine were: 1) 2 techniques using Jaffé's colorimetric reaction: one with rapid and the other with slow kinetics: 2) 2 more selective methods: enzymatic procedure and high performance liquid chromatography (HPLC). Measurements were performed in 13 multiple trauma patients after stabilization and in 5 comatose patients (control group) over a 3-day period, with strict 24-h urine collection. On the second day, inulin clearance and para-aminohippuric acid clearance (Cpah) were measured. Measurement of creatinine by Jaffé's procedure yields significantly higher levels than those obtained by the other methods. Higher levels of both plasma and urinary creatinine were observed in the multiple trauma patients with all the methods used. There were no significant differences in Ccr, Cin, Cpah between the multiple trauma patients and the control patients. The best correlations between inulin clearance and creatinine clearance were observed for Jaffé's rapid kinetics (r = 0.90) in the control group and for the enzymatic procedure in the multiple trauma group (r = 0.55). Plasma creatinine is not a useful indicator in multiple trauma. The correlation between creatinine clearance and inulin clearance is not very strong in multiple trauma, indicating that the relative evolution (not the absolute values) of creatinine clearance is of interest.

Adult↗
PubMed1990

Minimal model for signal-induced Ca2+ oscillations and for their frequency encoding through protein phosphorylation.

In a variety of cells, hormonal or neurotransmitter signals elicit a train of intracellular Ca2+ spikes. The analysis of a minimal model based on Ca2(+)-induced Ca2+ release from intracellular stores shows how sustained oscillations of cytosolic Ca2+ may develop as a result of a rise in inositol 1,4,5-trisphosphate (InsP3) triggered by external stimulation. This rise elicits the release of a certain amount of Ca2+ from an InsP3-sensitive intracellular store. The subsequent rise in cytosolic Ca2+ in turn triggers the release of Ca2+ from a second store insensitive to InsP3. In contrast to the model proposed by Meyer and Stryer [Meyer, T. & Stryer, L. (1988) Proc. Natl. Acad. Sci. USA 85, 5051-5055], the present model, which contains only two variables, predicts the occurrence of periodic Ca2+ spikes in the absence of InsP3 oscillations. Such results indicate that repetitive Ca2+ spikes evoked by external stimuli do not necessarily require the concomitant, periodic variation of InsP3. The model is closely related to that proposed by Kuba and Takeshita [Kuba, K. & Takeshita, S. (1981) J. Theor. Biol. 93, 1009-1031] for Ca2+ oscillations in sympathetic neurones, based on Ca2(+)-induced Ca2+ release. We extend their results by showing the minimal conditions in which the latter process gives rise to periodic behavior and take into account the role of the rise in InsP3 caused by external stimulation. The analysis further shows how signal-induced Ca2+ oscillations might be effectively encoded in terms of their frequency through the phosphorylation of a cellular substrate by a protein kinase activated by cytosolic Ca2+.

Animals↗
PubMed1990

Latency correlates with period in a model for signal-induced Ca2+ oscillations based on Ca2(+)-induced Ca2+ release.

Oscillations in cytosolic Ca2+ develop in a variety of cells after an induction phase, called latency, the duration of which depends on the magnitude of external stimulation. Experiments in hepatocytes indicate that the period and latency of Ca2+ oscillations both decrease as the level of the stimulus increases. We analyze the correlation between period and latency in a model recently proposed for signal-induced Ca2+ oscillations. We show that the linear relationship between period and latency observed in the experiments arises naturally in this model as a result of the mechanism of Ca2(+)-induced Ca2+ release on which it is based.

Animals↗
PubMed1990

Oscillatory dynamics in intercellular communication.

The role of biological rhythms in the control of intercellular communication is briefly reviewed. In particular, pulsatile cAMP signaling in the slime mold, Dictyostelium discoideum, the pulsatile release of the hormone GnRH in higher animals, and cytosolic calcium oscillations are discussed, with special reference to underlying molecular mechanisms. It is pointed out that there exists an optimal pattern of periodic stimulation by hormones and that frequency encoding has some advantages in comparison with amplitude encoding, especially concerning the accuracy of control.

Biological Clocks↗
PubMed1989

Are branched chain amino-acids beneficial for nutrition of severe surgical patients with sepsis?

UNLABELLED: This study investigated in severe sepsis the metabolic effects of two amino acid diets, including the same protein (0.3 gN/kg/day) and caloric intake (2g/kg/day glucose) but with different amino acid composition, 24% branched chain amino-acids (B.C.A.A.) for diet A (8 cases), 41% B.C.A.A. for diet B (11 cases). The two groups were obtained by randomisation at the operative day (D0) and were observed six days (D1-D6). During study, total nitrogen using a Kjeldhal method was measured. At D0 and D6, albumin, total hemolytic complement, transferrin, cholesterol, ammonaemia, insulin and amino acid pattern were studied in blood and skin tests were performed. The data were analysed by Mann-Whitney test. RESULTS: 1) The cumulative nitrogen balances of the six days are not significantly different, but at day 6 in diet B, patients started to be in an anabolic state (+3.7 gN) and in diet A catabolism persisted (-12 gN) (p<0.02). 2) Plasma B.C.A.A. are significantly higher and aromatic acids significantly lower in diet B. In order, Fischer ratio is also significantly different between the two regimens. All the other measured parameters are not significantly different. In this study, the B.C.A.A. enriched diet seems to be beneficial in surgical patients with severe sepsis.

Journal Article↗
PubMed1986

[Update on prolactin].

Normal serum prolactin levels range from 5 to 20 ng/ml (circadian rhythm, effect of stress, relation with estrogen secretion). Neuroleptics increase serum prolactin levels. Normal concentrations are restored within 24 to 48 hours of discontinuation of the drug. When neuroleptics are given for a long period of time, serum prolactin concentrations fall gradually to low levels. There is no conclusive evidence that prolactin plays a role in breast tumors in women. Epidemiologic studies have shown that neuroleptics are not responsible for increased incidences of these tumors.

Animals↗
PubMed1986

[Comparison of 2 semi-quantitative methods for evaluating blood glucose in newborn infants].

Blood glucose levels were assessed in 49 neonates, using 2 blood glucose test strips. Results were compared to blood glucose levels. Correlations between values from the test strips and values from the laboratory were better using the Haemo-Glukotest (r = 0.91) than using the Dextrostix (r = 0.82). As compared to values from the laboratory, however, both glucose test strips gave higher values and did not properly identify all cases of hypoglycemia.

Blood Glucose↗
PubMed1979

[Interaction between an antifungal heptaene, amphotericin B and cholesterol in vitro, as detected by circular dichroism and absorption. Influence of temperature].

The polyene antibiotic "Amphotericin B" can interact with sterols, cholesterol or ergosterol in aqueous and hydroalcoholic media and a correlative striking spectral change appears between 300 and 420 nm in the CD and absorption spectra. Using these spectroscopic methods we have determined that the influence of temperature between 4 and 80 degrees C is very important. The higher the temperature the most rapid is the modification of the spectra. Thus, the "Amphotericin B"-sterol complex is more easily formed when heating. We have not found any reversibility at 80 degrees C.

Amphotericin B↗