A model of glucose transport and conversion to lactate in the renal medullary microcirculation

2006 ◽  
Vol 290 (1) ◽  
pp. F87-F102 ◽  
Author(s):  
Wensheng Zhang ◽  
Aurélie Edwards
Keyword(s):  
Lactate Concentration ◽  
Anaerobic Glycolysis ◽  
Kinetic Rate Constant ◽  
Outer Medulla ◽  
Kinetic Rate ◽  
Corticomedullary Junction ◽  
Vasa Recta ◽  
Countercurrent Exchange ◽  
Parameter Values ◽  
Good Agreement

In this study, we modeled mathematically the transport of glucose across renal medullary vasa recta and its conversion to lactate by anaerobic glycolysis. Uncertain parameter values were determined by seeking good agreement between predictions and experimental measurements of lactate generation rates, as well as glucose and lactate concentration ratios between the papilla and the corticomedullary junction; plausible kinetic rate constant and permeability values are summarized in tabular form. Our simulations indicate that countercurrent exchange of glucose from descending (DVR) to ascending vasa recta (AVR) in the outer medulla (OM) and upper inner medulla (IM) severely limits delivery to the deep inner medulla, thereby limiting medullary lactate generation. If the permeability to glucose of OMDVR and IMDVR is taken to be the same and equal to 4 × 10−4 cm/s, the fraction of glucose that bypasses the IM is calculated as 54%; it is predicted as 37% if the presence of pericytes in OMDVR reduces the glucose permeability of these vessels by a factor of 2 relative to that of IMDVR. Our results also suggest that red blood cells (RBCs) act as a reservoir that reduces the bypass of glucose from DVR to AVR. The rate of lactate generation by anaerobic glycolysis of glucose supplied by blood from glomerular efferent arterioles is predicted to range from 2 to 8 nmol/s, in good agreement with lower estimates obtained from the literature (Bernanke D and Epstein FH. Am J Physiol 208: 541–545, 1965; Bartlett S, Espinal J, Janssens P, and Ross BD. Biochem J 219: 73–78, 1984).

Oxygen transport across vasa recta in the renal medulla

2002 ◽  
Vol 283 (3) ◽  
pp. H1042-H1055 ◽  
Author(s):  
Wensheng Zhang ◽  
Aurélie Edwards
Keyword(s):  
Oxygen Transport ◽  
Renal Medulla ◽  
Blood Flow Rate ◽  
Sodium Reabsorption ◽  
Corticomedullary Junction ◽  
Vasa Recta ◽  
Oxygen Requirements ◽  
Experimental Findings ◽  
Parameter Values ◽  
Baseline Parameter

In this model of oxygen transport in the renal medullary microcirculation, we predicted that the net amount of oxygen reabsorbed from vasa recta into the interstitium is on the order of 10−6 mmol/s, i.e., significantly lower than estimated medullary oxygen requirements based on active sodium reabsorption. Our simulations confirmed a number of experimental findings. Low medullary Po 2results from the countercurrent arrangement of vessels and an elevated vasa recta permeability to oxygen, as well as high metabolic needs. Diffusional shunting of oxygen between descending vasa recta (DVR) and ascending vasa recta also explains why a 20-mmHg decrease in initial Po 2 at the corticomedullary junction only leads to a small drop in papillary tip Po 2 (<2 mmHg with baseline parameter values). Conversely, small changes in the consumption rate of DVR-supplied oxygen, in blood flow rate, in hematocrit, or in capillary permeability to oxygen, beyond certain values sharply reduce interstitial Po 2. Without erythrocytes, papillary tip Po 2 cannot be maintained above 10 mmHg, even when oxygen consumption is zero.

scholarly journals CO2 Induced Foaming Behavior of Polystyrene near the Glass Transition

2017 ◽  
Vol 2017 ◽  
pp. 1-15
Author(s):  
Salah Al-Enezi
Keyword(s):  
Experimental Data ◽  
High Pressure ◽  
Glass Transition ◽  
Dissolved Gas ◽  
Foaming Process ◽  
Foaming Behavior ◽  
Potential Applications ◽  
Model C ◽  
Parameter Values ◽  
Good Agreement

This paper examines the effect of high-pressure carbon dioxide on the foaming process in polystyrene near the glass transition temperature and the foaming was studied using cylindrical high-pressure view cell with two optical windows. This technique has potential applications in the shape foaming of polymers at lower temperatures, dye impregnation, and the foaming of polystyrene. Three sets of experiments were carried out at operating temperatures of 50, 70, and 100°C, each over a range of pressures from 24 to 120 bar. Foaming was not observed when the polymer was initially at conditions below Tg but was observed above Tg. The nucleation appeared to occur randomly leading to subsequent bubble growth from these sites, with maximum radius of 0.02–0.83 mm. Three models were applied on the foaming experimental data. Variable diffusivity and viscosity model (Model C) was applied to assess the experimental data with the WLF equation. The model shows very good agreement by using realistic parameter values. The expansion occurs by diffusion of a dissolved gas from the supersaturated polymer envelope into the bubble.

A Canonical Neural Circuit for Cortical Nonlinear Operations

2008 ◽  
Vol 20 (6) ◽  
pp. 1427-1451 ◽  
Author(s):  
Minjoon Kouh ◽  
Tomaso Poggio
Keyword(s):  
Neural Circuit ◽  
Neural Responses ◽  
Energy Models ◽  
Divisive Normalization ◽  
Primate Visual Cortex ◽  
Neurophysiological Data ◽  
Ventral Pathway ◽  
Response Profiles ◽  
Parameter Values ◽  
Good Agreement

A few distinct cortical operations have been postulated over the past few years, suggested by experimental data on nonlinear neural response across different areas in the cortex. Among these, the energy model proposes the summation of quadrature pairs following a squaring nonlinearity in order to explain phase invariance of complex V1 cells. The divisive normalization model assumes a gain-controlling, divisive inhibition to explain sigmoid-like response profiles within a pool of neurons. A gaussian-like operation hypothesizes a bell-shaped response tuned to a specific, optimal pattern of activation of the presynaptic inputs. A max-like operation assumes the selection and transmission of the most active response among a set of neural inputs. We propose that these distinct neural operations can be computed by the same canonical circuitry, involving divisive normalization and polynomial nonlinearities, for different parameter values within the circuit. Hence, this canonical circuit may provide a unifying framework for several circuit models, such as the divisive normalization and the energy models. As a case in point, we consider a feedforward hierarchical model of the ventral pathway of the primate visual cortex, which is built on a combination of the gaussian-like and max-like operations. We show that when the two operations are approximated by the circuit proposed here, the model is capable of generating selective and invariant neural responses and performing object recognition, in good agreement with neurophysiological data.

Localization of angiotensin II type 1 receptor subtype mRNA in rat kidney

1995 ◽  
Vol 268 (2) ◽  
pp. F220-F226 ◽  
Author(s):  
D. P. Healy ◽  
M. Q. Ye ◽  
M. Troyanovskaya
Keyword(s):  
In Situ Hybridization ◽  
Rat Kidney ◽  
At1 Receptor ◽  
Receptor Subtypes ◽  
Mrna Levels ◽  
Ang Ii ◽  
Outer Medulla ◽  
Vasa Recta

The physiological effects of angiotensin II (ANG II) on the kidney are mediated primarily by the ANG II type 1 (AT1) receptor. Two highly similar AT1 receptor subtypes have been identified in the rat by molecular cloning techniques, namely AT1A and AT1B. The intrarenal localization of the AT1A and AT1B receptor subtypes has not been studied by hybridization methods with subtype-specific receptor probes. Using radiolabeled probes from the 3' noncoding region of the AT1A and AT1B cDNAs, we localized AT1 mRNA in rat kidney by in situ hybridization. Specificity of the 3' noncoding region probes was tested by Northern blot and solution hybridization methods. AT1A mRNA levels were highest in the liver, kidney, and adrenal. In contrast, AT1B mRNA levels were highest in the adrenal and pituitary and low in kidney. Autoradiographic localization of 125I-[Sar1,Ile8]ANG II binding indicated that the highest levels of AT1 receptors were found in glomeruli and vascular elements. In situ hybridization with a nonselective AT1 receptor riboprobe indicated that the highest levels of AT1 mRNA were in the outer medullary vasa recta and cortical glomeruli with additional diffuse labeling of the cortex and outer medulla, consistent with labeling of tubular elements. In contrast, in situ hybridization with the AT1 subtype selective probes revealed that AT1A receptor mRNA was primarily localized to the vasa recta and diffusely to the outer stripe of the outer medulla and the renal cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Computer Simulation of a Test Rig to Model Sloshing in Spin-Stabilized Satellites

1992 ◽  
Vol 114 (4) ◽  
pp. 689-698 ◽  
Author(s):  
D. R. Flugrad ◽  
L. A. Obermaier
Keyword(s):  
Model Simulation ◽  
Test Rig ◽  
Dynamic Motion ◽  
Experimental Project ◽  
Rotating Structure ◽  
Simulation Results ◽  
Parameter Values ◽  
The Mathematical Model ◽  
Two Degree Of Freedom ◽  
Good Agreement

Certain communications satellites carry liquid stores on board for station tending and attitude adjustment. However, sloshing of the liquid can cause an undesirable nutational motion of the spin-stabilized vehicle. In previous work a test rig was designed, built and instrumented to study the interaction between the rotating structure and liquid. To augment that experimental project, a computer model of the test rig has been developed to simulate the dynamic motion of the system for various parameter values. The sloshing liquid was replaced by a two degree-of-freedom pendulum in the mathematical model. Simulation results were compared with those from a general multibody dynamics program and with experimental measurements of the test rig motion to demonstrate the mathematical model’s validity. Good agreement was achieved in both instances.

Renal medullary blood flow: its measurement and physiology

1986 ◽  
Vol 64 (7) ◽  
pp. 873-880 ◽  
Author(s):  
W. A. Cupples
Keyword(s):  
Blood Flow ◽  
Renal Medulla ◽  
Vascular Bundles ◽  
Medullary Blood Flow ◽  
Vasa Recta ◽  
Countercurrent Exchange ◽  
Renal Medullary Blood Flow ◽  
Urinary Concentrating Ability ◽  
Velocity Tracking ◽  
Uptake Method

The vasculature of the mammalian renal medulla is complex, having neither discrete input nor output. There is also efficient countercurrent exchange between ascending and descending vasa recta in the vascular bundles. These considerations have hampered measurement of medullary blood flow since they impose pronounced constraints on methods used to assess flow. Three main strategies have been used: (i) indicator extraction; (ii) erythrocyte velocity tracking; and (iii) indicator dilution. These are discussed with respect to their assumptions, requirements, and limitations. There is a consensus that medullary blood flow is autoregulated, albeit over a narrower pressure range than is total renal blood flow. When normalized to gram tissue weight, medullary blood flow in the dog is similar to that in the rat, on the order of 1 to 1.5 mL∙min−1∙g−1. This is considerably greater than estimated by the radioiodinated albumin uptake method which has severe conceptual and practical problems. From both theoretical and experimental evidence it ssems that urinary concentrating ability is considerably less sensitive to changes in medullary blood flow than is often assumed.

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