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At least 793 records · Page 44Linked to original sources
PubMed1994

Hydrogen ion compartmentation during and following cerebral ischemia evaluated by 31P NMR spectroscopy.

Two peaks were observed in the inorganic phosphate region in 31P NMR spectra obtained during and shortly after incomplete forebrain ischemia induced in rats under normoglycemic conditions. Pre-ischemia, a single Pi peak was observed at a chemical shift of 2.5 ppm (pH 7.2). This peak shifted upfield to 1.6 ppm (pH 6.5) and, following reperfusion, returned to its pre-ischemia value. During ischemia and for a short time following reperfusion, a second, smaller peak was observed which we assigned to a second pool of inorganic phosphate. The data support the proposal by Kraig and coworkers of pH compartmentation between neurons and glia during and following transient forebrain ischemia.

Animals↗
PubMed1977

A short parameter-fitting routine for compartmental models.

We have developed a program of 298 FORTRAN statements which obtains the inter-pool exchange rates and other parameters of a compartmental system, working directly from the time course of tracer activity after a bolus injection. The fitting problem - data and model - is specified by the user in a natural syntactic style. The program calculates least-squares estimates, confidence limits and intercorrelation estimates for the fitted parameters. Its small size and conceptual simplicity make the program a powerful practical tool for analyzing tracer studies.

Computers↗
PubMed1986

A program in BASIC for calculation of tissue ion flux rates, rate constants, and cellular ion contents and concentrations for a three compartmental serial model.

A BASIC program is presented to calculate tissue ion flux rates, rate constants, and cellular ion contents and concentrations from ion flux curves. For the purpose of this program, the biological tissue will be treated as a three compartmental series model. The program requires that eight experimentally determined variables be entered for each ion species to be analyzed: the experimental slope and intercept variables for each phase of the flux curve, the wet and dry tissue weights, the known or estimated value of extracellular space and the measured or known value of the cellular surface to volume ratio of the particular tissue being studied. All other required input data are obtained from the literature or experimental protocol and may be treated as constants. This program was designed for the in vitro determination of ion exchange in skeletal muscle but may be used with little or no modification for flux measurements in other tissues.

Animals↗
PubMed1989

Computer software for development and simulation of compartmental models of neurons.

A software package 'Nodus' for simulation and development of compartmental models of neurons is described. Passive or excitable membranes with voltage dependent ion conductances or synaptic conductances can be modeled. Detailed simulations of morphology and electrophysiology of neurons are possible. Neurophysiological experiments like voltage clamps and complex current injections can be simulated. Two integration methods are available: a fast hybrid method and an accurate fifth order Runge-Kutta method, with variable time steps. Nodus is implemented on Apple Macintosh microcomputers, with the standard user interface and interactive graphics. Simulations of simple test models demonstrate the accuracy and computation speed of the application.

Computer Simulation↗
PubMed1994

MAMCAT: an expert system for distinguishing between mammillary and catenary compartmental models.

MAMCAT is a user-friendly, interactive, graphics-based PC program for addressing a common compartmental model discrimination problem in the framework of model indistinguishability theory: can mammillary and catenary models of the same order be distinguished from each other? The software is designed to teach the theory and solve specific problems. The user is guided step-by-step through definitions, examples, theory and problem solution. Topological properties are used first to screen out some distinguishable models and thereby reduce the number of candidates for indistinguishability. Transfer function analysis is then used to explore the remaining candidates. Analytical results for up to 5-compartment models are given and a more general algorithm is induced from these results.

Algorithms↗
PubMed1986

Cortico-cortical associations and EEG coherence: a two-compartmental model.

EEG coherence was computed from 19 scalp locations from 189 children ranging in age from 5 to 16 years. Tests of spatial homogeneity of EEG coherence were conducted by comparing EEG coherence as a function of different interelectrode distances in the anterior-to-posterior versus posterior-to-anterior directions. Highly significant inhomogeneities were observed since greater coherence was present in the anterior-to-posterior direction than in the posterior-to-anterior directions. Greater coherence was also present in frontal derivations than in posterior derivations and from the right hemisphere in comparison to the left hemisphere. These data indicate that at least two separate sources of EEG coherence were present (1) coherence produced through the action of short length axonal connections, and (2) coherence produced through the action of long distance connections. Measures of phase delays as a function of interelectrode distance supported the development of a 'two-compartmental' model of EEG coherence in which different features of coherence are produced by different length fiber systems. Based on this model a number of hypotheses were developed to explain differences in connectivity between left and right hemispheres and frontal versus occipital cortex.

Adolescent↗
PubMed1986

Compartmental prostaglandin release by angiotensin II and arginine-vasopressin in rabbit isolated perfused kidneys.

The compartmental effects of angiotensin II (AII) and arginine-vasopressin (AVP) on renal prostaglandin (PG) formation were studied in the isolated perfused kidney of the rabbit by superfusion bioassay of venous and ureteral effluents (VE and UE) and radioimmunoassay (RIA). Comparable results were obtained with either bioassay or RIA when used to quantitate renal PG release. The effects on PG release into the VE were similar for AII and AVP, as were their pressor responses. However, their effects on PG release into the UE differed markedly. AII resulted in a 6-fold greater urinary efflux than venous of bioassayable PGs, whereas AVP-induced PG release into UE was slightly less than PG efflux into the VE at all doses of the peptide. The profile of released PGs varied according to the sampling source (VE or UE). Moreover, each peptide released a similar profile of PGs at all doses, i.e. UE PGE2 greater than PGF2 alpha greater than 6-keto PGF1 alpha; VE PGE2 greater than 6-keto PGF1 alpha greater than PGF2 alpha (TxB2 was not detected in either effluent). Thus, renal vascular PG release is similar for the vasoactive peptides, AII and AVP, whereas the urinary efflux of PGs is considerably greater in response to AII.

6-Ketoprostaglandin F1 alpha↗
PubMed1990

Vertical compartmentation and cellular transformations in the germinal matrices of the embryonic rat cerebral cortex.

Cellular compartmentation was studied in the germinal matrices (the primary neuroepithelium and the subventricular zone) of the rat cerebral cortex at successive stages of embryonic development. Three sets of materials were used: methacrylate-embedded brain sections from normal embryos, autoradiograms from embryos labeled with [3H]thymidine, and methacrylate-embedded sections from embryos exposed to 200 R X-ray. Examination of normal specimens showed that between Embryonic Day 12 (E12) and E15 the cortical germinal matrix consists only of a primary neuroepithelium. By Day E16, a subventricular zone has formed in the early developing ventrolateral aspect of the cortex. The subventricular zone grows in depth for several days, while at the same time the depth of the neuroepithelium decreases. Examination of short-survival thymidine radiograms revealed that the labeled cells do not form a continuous band in the neuroepithelium but aggregate in patches reminiscent of bunches of grapes strung one a line. It is postulated that this vertical periodicity is due to the alternation of cell aggregates with short and long cell cycle times. Finally, examination of the cortical neuroepithelium in rats exposed to 200 R X-ray showed that there is an alternation of radiosensitive (collapsing) and radioresistant (intact) patches that roughly correspond in size to the labeled and unlabeled patches seen in autoradiograms. Additional observations concern the onset of local cell proliferation in the white matter at late stages of fetal development and the transformation of the neuroepithelium into a matrix producing ependymal cells.

Animals↗
PubMed1992

The role of adenylate kinase in dynamic compartmentation of adenine nucleotides in the mitochondrial intermembrane space.

To investigate the existence of dynamic adenine nucleotide (AdN) compartment in the mitochondrial intermembrane space, we used reconstituted systems consisting of (i) functional intact liver and heart mitochondria and (ii) pyruvate kinase plus phosphoenolpyruvate, both competing for ADP either formed in the intermembrane space by adenylate kinase or added directly into, or regenerated by ATPase within, the extramitochondrial space. It is shown that ADP formation in the mitochondrial intermembrane space is a prerequisite for a dominating oxidative phosphorylation in reconstituted systems, suggesting dynamic ADP compartmentation in that space.

Adenosine Diphosphate↗
PubMed1992

Compartmentation of dCTP pools disappears after hydroxyurea or araC treatment in lymphocytes.

The calculated rate of DNA synthesis using [5-3H]TdR was about 4 times higher than in the case of [5-3H]CdR labeling, even after correction for the specific radioactivities of the intracellular pools. These data show a compartmentation of dCTP pools in lymphocytes. Hydroxyurea increased the specific activities of both dTTP and dCTP pools so that the calculated rate of DNA synthesis became equal. The same effect was found for araC treatment, but not for fluorodeoxyuridine. dCTP was supplied from CTP which is the lowest ribonucleotide pool in lymphocytes. Different functions of the two dCTP pools are proposed: one serving DNA replication; the other one supplies phospholipid precursors and DNA repair.

Cytarabine↗
PubMed1993

Compositional compartmentalization of the nuclear genomes of Trypanosoma brucei and Trypanosoma equiperdum.

High molecular weight DNA preparations from Trypanosoma brucei and Trypanosoma equiperdum were fractionated by preparative centrifugation in a Cs2SO4 density gradient in the presence of BAMD, bis(acetatomercurimethyl)dioxane, a sequence-specific DNA ligand. Analytical centrifugation in CsCl of the DNA fractions so obtained showed that both DNAs had a bimodal distribution with two major peaks banding at 1.702-1.703 and 1.708 g/cm3 and representing 1/3 and 2/3 of total DNA, respectively. Several minor components were also detected. These results indicate that a compositional compartmentalization is not only found in the genome of vertebrates and plants, as already described, but also in those of protozoa such as Trypanosomes.

Animals↗
PubMed1975

A strategy of approaching the fit of a compartmental model applied to the behaviour of aspirins in humans.

A compartmental model has been set up with five parts. Formulation and testing of the model have been performed by simultaneous experiments involving measurement of blood levels of ASA and SA for four different preparations of aspirin investigated in four different patients. The hypotheses of the present study had been based upon a four-compartment model. However, such a model did not appear to be adequate and a new model with five compartments has been substituted for the former one. The five-compartment model has led to the formulation and testing of new physiological hypotheses; it has also provided the development of a fitting method using powerful convergence algorithms. A general analytical formulation has been set up which has made it possible to circumscribe the multiple roots of the characteristic polynomial when they have to be taken into consideration.

Aspirin↗
PubMed1976

[Compartmental model of the adsorption of a dye by proteins. The possible role of adsorption in the hepatic excretion of bromosulphophthalein].

A compartmental model was suggested for the study of the hepatic excretion of bromosulphophthalein (BSP). By using a hypothesis concerning the adsorption of the BSP compound by proteins, one derives from the equations of the model several known experimental results, viz. form of concentration curves that vary in accordance with the strength of the injection, existence of a limiting Tm value, etc. An explicit formula is given for calculating Tm.

Adsorption↗
PubMed1980

Estimation, resolution and solvability of linear compartmental models: cholesterol metabolism in man.

The paper presents a method to test metabolic linear multicompartment models for their mathematical solvability and their power of resolution with respect to individual parameters. The method can be seen as a means of predicting not only the model theoretical identifiability but also the expected quality of estimation before undertaking any actual serial experiments. The compartmental model of human cholesterol metabolism is taken as a demonstrative problem. The analysis shows that it is possible with tracer techniques to measure the cholesterol turnover, the cholesterol fluxes between exchangeable cholesterol pools, the cholesterol masses in individual pools, and the endogenous cholesterol synthesis in individual pools if certain conditions are met. In any complex kinetic situation, performance of a systematic model analysis is recommended before embarking on large-scale experimentation.

Body Fluid Compartments↗
PubMed1987

A stochastic compartmental model of bone cells.

Cellular dynamics play an important role in bone remodelling. The mesenchymal cells, osteoclasts, osteoblasts and osteocytes are the four types of bone cells, which mediate bone remodelling involving bone formation and resorption throughout the human life-span. A stochastic compartmental model of bone cells is formulated in the present analysis assuming these four types of cells to be in four distinct compartments. The cumulant generating function is first derived using the transition parameters for intercompartmental diffusion. Equations for the mean, variance and covariance for the number density of these cells are then derived from the partial differential equation for the cumulant generating function. The simulation results are consistent with previous experimental observations.

Bone Development↗
PubMed1991

Identification of compartmental models for perturbed cell populations using state-space parameter estimation techniques.

Multiple compartment models for describing synchronous cell kinetics in which cell populations are characterized by DNA content are reviewed. These models are useful for understanding and predicting a cell population's dynamic response to perturbations induced by drugs or radiation. A practical approach is proposed for determining the parameters of these models from empirical cell-cycle data. Specifically, a state-space parameter estimation algorithm based on the maximum likelihood method--developed and coded primarily for engineering applications and commercially available for personal computers and minicomputers--can be applied to DNA specific cell-cycle measurements from synchronized cell populations to produce model parameter estimates. This is demonstrated using published data from a cell-cycle experiment. The results show that the procedure works well, and that with careful experimental planning even better results should be possible. Since the compartmental model is often used to represent biological systems, this approach is widely applicable.

Algorithms↗
PubMed1986

Fatigue in isometric contraction in a single muscle fibre: a compartmental calcium ion flow model.

Fatigue in muscle is a complex biological phenomenon which has so far eluded a definite explanation. Many biochemical and physiological models have been suggested in the literature to account for the decrement in the ability of muscle to sustain a given level of force for a long time. Some of these models have been critically analysed in this paper and are shown to be not able to explain all the experimental observations. A new compartmental model based on the intracellular calcium ion movement in muscle is proposed to study the mechanical responses of a muscle fibre. Computer simulation is performed to obtain model responses in isometric contraction to an impulse and a train of stimuli of long duration. The simulated curves have been compared with experimentally observed mechanical responses of the semitendinosus muscle fibre of Rana pipiens. The comparison of computed and observed responses indicates that the proposed calcium ion model indeed accounts very well for the muscle fatigue.

Animals↗
PubMed1988

A non-steady compartmental flow model of the cerebrovascular system.

A lumped parameter compartmental model for the cerebrovascular fluid system is constructed and solved for the general linear problem of a nonsteady flow with constant resistances and compliances. The model predicts the intracranial pressure waves in the various compartments of the brain in response to pressure changes in the vascular system.

Blood-Brain Barrier↗