Kinetics of potassium uptake in red spruce seedlings

1985 ◽  
Vol 63 (3) ◽  
pp. 512-516
Author(s):  
J. R. Cumming ◽  
R. T. Eckert ◽  
L. S. Evans
Keyword(s):  
Nonlinear Least Squares ◽  
Theoretical Models ◽  
Potassium Uptake ◽  
Red Spruce ◽  
Saturation Kinetics ◽  
Potassium Absorption ◽  
Parameter Values ◽  
Kinetics Of ◽  
Diffusive Component ◽  
Nutrient Solutions

Potassium uptake by roots of 3-week-old red spruce (Picea rubens Sarg.) seedlings was measured in nutrient solutions ranging in K+ concentration from 0.01 to 10.0 mM. Nonlinear least squares analysis was used to estimate uptake parameters Vmax and Km. Analyses of residuals generated by several theoretical models of ion uptake were undertaken to choose the best mechanistic uptake model. Potassium absorption by red spruce seedlings was characterized by Michaelis–Menten behavior from K+ solutions in the range 0.01 to 1.0 mM. Above 1.0 mM, accumulation of potassium was most readily accounted for by a linear diffusive component superimposed on saturation kinetics. Uptake parameter values of Vmax = 1.17 μmol K∙g fresh weight−1∙h−1 and Km = 0.083 mM were similar to those reported for other species. The culture of seedlings in full-strength nutrient solution did not reduce the ability to resolve these uptake parameters in short-term experiments.

Absorption of Galactose by the Rat Small Intestine in Vivo: Proximal—Distal Kinetic Gradients and a New Method to Express Absorption Per Enterocyte

1976 ◽  
Vol 50 (6) ◽  
pp. 499-509 ◽  
Author(s):  
R. M. Batt ◽  
T. J. Peters
Keyword(s):  
Small Intestine ◽  
Absorptive Capacity ◽  
Proximal Jejunum ◽  
Rat Small Intestine ◽  
Experimental Conditions ◽  
Carrier Mediated Transport ◽  
Saturation Kinetics ◽  
Kinetics Of ◽  
Diffusive Component

1. The absorption in vivo of d-galactose by the rat small intestine has been examined in proximal jejunum and distal ileum by use of a recirculation—perfusion technique. 2. Multiple sequential perfusions over 4 h produced no subsequent functional or morphological damage in the perfused segments. 3. Absorption of galactose from 8 and 64 mmol/l solutions was found to be independent of flow rate over the range 1·0–6·5 ml/min. 4. Galactose absorption in both the jejunum and the ileum exhibited saturation kinetics of the Michaelis—Menten type, and phlorrhizin sensitivity. Sorbose was only absorbed minimally. These observations demonstrate that galactose is absorbed by carrier-mediated transport and that there is no significant passive diffusive component in vivo. 5. Under the stated experimental conditions, the maximum absorptive capacity was 4·5 times greater in the jejunum than in the ileum. The Michaelis constant for galactose was higher in the jejunum than in the ileum. 6. Enterocytes were isolated from perfused segments and quantified by DNA assay with a correction for yield. In this manner, the absorptive capacity per enterocyte was calculated. 7. The maximum absorptive capacity per enterocyte was 3·5 times greater in the jejunum than in the ileum.

Effect of aluminum on potassium uptake by red spruce seedlings

1985 ◽  
Vol 63 (6) ◽  
pp. 1099-1103 ◽  
Author(s):  
J. R. Cumming ◽  
R. T. Eckert ◽  
L. S. Evans
Keyword(s):  
Kinetic Analysis ◽  
Kinetic Parameters ◽  
Nonlinear Least Squares ◽  
Potassium Uptake ◽  
Red Spruce ◽  
Physiological Changes ◽  
Absorption Data ◽  
Aluminum Exposure ◽  
Initial Decrease ◽  
Seedling Roots

Potassium uptake by roots of intact red spruce seedlings exposed to 0, 1, and 4 mg∙L−1 Al3+ was determined using kinetic analysis. Uptake parameters Vmax and Km were estimated by nonlinear least-squares analysis of K+ absorption data fitted to a combined active and linear uptake model. Roots treated with 1 mg∙L−1 Al exhibited enhanced potassium uptake for up to 72 h of aluminum exposure. K+ uptake in the presence of 4 mg∙L−1 Al also increased but was influenced by the duration of exposure to Al in solution. Comparison of kinetic parameters revealed an increase in Vmax in roots treated with aluminum. Km in both 1 and 4 mg∙L−1 aluminum treatments varied consistently with duration of exposure, characterized by an initial decrease in apparent carrier-site affinity followed by Km values trending toward control levels. These changes are hypothesized to result from a combination of physical and physiological changes in red spruce seedling roots induced by Al3+ in solution.

REFRACTIVE INDEX PROFILE RECONSTRUCTION OF PLANAR WAVEGUIDE FROM ITS MODE INTENSITY USING CHARACTERISTIC MATRIX METHOD

2001 ◽  
Vol 10 (02) ◽  
pp. 169-179
Author(s):  
HENRI P. URANUS ◽  
M. O. TJIA
Keyword(s):  
Refractive Index ◽  
Intensity Distribution ◽  
Planar Waveguide ◽  
Nonlinear Least Squares ◽  
Refractive Index Profile ◽  
Characteristic Matrix ◽  
Least Squares Regression ◽  
Index Profile ◽  
Measured Intensity ◽  
Parameter Values

A method is proposed for the reconstruction of refractive index profile of planar waveguide from its fundamental mode intensity profile. The reconstruction is performed by fitting the calculated intensity distribution iteratively with the measured intensity distribution employing nonlinear least-squares regression technique. At each stage of iteration, new trial parameter values are generated and used to form a waveguide model approximated by a multilayer structure with stepwise index distribution, upon which the intensity distribution is then calculated by using the characteristic matrix technique. This method was numerically examined by using samples of either known or unknown analytic expression of the index profile.

scholarly journals A Logistic Approach for Kinetics of Isothermal Pyrolysis of Cellulose

Processes ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 551
Author(s):  
Jorge López-Beceiro ◽  
Ana María Díaz-Díaz ◽  
Ana Álvarez-García ◽  
Javier Tarrío-Saavedra ◽  
Salvador Naya ◽  
...  
Keyword(s):  
Kinetic Model ◽  
Time Derivative ◽  
Inert Atmosphere ◽  
Second Step ◽  
Rate Parameter ◽  
Thermogravimetric Data ◽  
Different Temperatures ◽  
Parameter Values ◽  
Kinetics Of ◽  
Logistic Functions

A kinetic model is proposed to fit isothermal thermogravimetric data obtained from cellulose in an inert atmosphere at different temperatures. The method used here to evaluate the model involves two steps: (1) fitting of single time-derivative thermogravimetric curves (DTG) obtained at different temperatures versus time, and (2) fitting of the rate parameter values obtained at different temperatures versus temperature. The first step makes use of derivative of logistic functions. For the second step, the dependence of the rate factor on temperature is evaluated. That separation of the curve fitting from the analysis of the rate factor resulted to be very flexible since it proved to work for previous crystallization studies and now for thermal degradation of cellulose.

Tetraethylammonium transport by isolated perfused snake renal tubules

1984 ◽  
Vol 246 (4) ◽  
pp. F476-F487 ◽  
Author(s):  
C. T. Hawk ◽  
W. H. Dantzler
Keyword(s):  
Transepithelial Transport ◽  
Renal Tubules ◽  
Chemical Gradient ◽  
Saturation Kinetics ◽  
Sodium Dependency ◽  
Diffusive Component

Tetraethylammonium (TEA) transport was studied in isolated perfused snake (Thamnophis spp.) proximal renal tubules. Unidirectional lumen-to-bath (J1----bTEA) and bath-to-lumen (J1----bTEA) fluxes exhibited saturation kinetics, but Jb----1TEA also exhibited an apparent diffusive component and J1----bTEA did not. Jb----1TEA exceeded J1----bTEA at all concentrations studied, resulting in net TEA secretion. Transport into cells across both luminal and peritubular membranes was apparently against an electro-chemical gradient and was inhibited by cyanide. Km for J1----bTEA (5.9 microM) was about one-third Km for Jb----1TEA (19.9 microM), indicating greater affinity of the luminal transporter for TEA; but Vmax for Jb----1TEA (153 fmol X min-1 X mm-1) was about six times Vmax for J1----bTEA (27 fmol X min-1 X mm-1), indicating a greater capacity of the peritubular transporter for TEA, which could account for net TEA secretion. Jb----1TEA was inhibited by N-methylnicotinamide (NMN) in the bath, but J1----bTEA was inhibited initially and then apparently transstimulated by NMN in the lumen, indicating possible countertransport. J1----bTEA, but not Jb----1TEA, was significantly reduced by replacement of sodium with sucrose, indicating possible sodium dependency of the luminal transporter. All data indicate active (either primary or secondary) TEA transport at both luminal and peritubular membranes but net transepithelial transport in the bath-to-lumen direction.

Kinetics of hepatic alanine uptake and urea synthesis in pigs

1988 ◽  
Vol 254 (4) ◽  
pp. G602-G609
Author(s):  
H. Vilstrup ◽  
L. T. Skovgaard
Keyword(s):  
Maximum Rate ◽  
Maximum Likelihood Method ◽  
Blood Flow Rate ◽  
Likelihood Method ◽  
Synthesis Rate ◽  
Urea Synthesis ◽  
Half Maximum ◽  
Concentration Gradients ◽  
Saturation Kinetics ◽  
Kinetics Of

The kinetics of hepatic alanine uptake and urea synthesis in relation to sinusoid alanine concentration was investigated in seven anesthetized pigs weighing 63 kg, using liver vein catheterizations. Each experiment consists of four steady-state periods of 40 min with alanine concentrations in the range of 0.4-27 mmol/l. The process rates were measured as the products of transhepatic concentration gradients and hepatic blood flow rate, determined by indocyanine green. The data suggest that both processes follow saturation kinetics, that there exists a sinusoidal concentration of alanine below which net removal is limited, and that urea synthesis consists of two components: one alanine independent and one depending on alanine concentration according to Michaelis-Menten kinetics. The kinetic parameters were estimated iteratively by the maximum likelihood method. The maximum rate of alanine uptake was 1.13 +/- 0.74 mmol.min-1.kg liver wt-1 (mean +/- SD), the alanine concentration resulting in half-maximum alanine uptake rate was 1.69 +/- 0.99 mmol/l, and the removal-limiting alanine concentration was 0.27 +/- 0.09 mmol/l. The maximum rate of urea-N synthesis was 1.49 +/- 0.87 mmol.min-1.kg liver wt-1, the alanine concentration resulting in half-maximum urea-N synthesis rate was 2.32 +/- 1.11 mmol/l, and the alanine concentration-independent urea-N synthesis rate was 0.13 +/- 0.10 mmol.min-1.kg liver wt-1.

Increasing magnesium intakes in relation to magnesium absorption in dry cows

2004 ◽  
Vol 71 (3) ◽  
pp. 297-303 ◽  
Author(s):  
Surasak Jittakhot ◽  
J Thomas Schonewille ◽  
Hugo Wouterse ◽  
Anton WJ Uijttewaal ◽  
Chalermpon Yuangklang ◽  
...  
Keyword(s):  
Dairy Cow ◽  
Dry Matter ◽  
Rumen Fluid ◽  
Latin Square ◽  
Basal Diet ◽  
Apparent Absorption ◽  
Post Feeding ◽  
Saturation Kinetics ◽  
Kinetics Of

Earlier studies with temporarily isolated rumen of heifers show saturation kinetics of Mg efflux across the rumen wall. Therefore, we hypothesized that high Mg intakes would not further increase the rate of Mg absorption in cows. To test our hypothesis, six ruminally fistulated non-pregnant dry cows were given diets with different Mg concentrations in a 6×6 Latin square design. Desired concentrations of Mg were attained by adding MgO to the basal diet and the Mg concentrations in the total rations were 3·8, 6·4, 9·1, 11·8, 14·1 and 17·3 g Mg/kg dry matter, which provided Mg intakes of 27·1, 44·6, 64·6, 83·5, 100·4 and 124·3 g/d, respectively. Increasing Mg intakes were associated with increased (P<0·001) faecal Mg excretion. However, apparent Mg absorption expressed as g/d was not significantly different for Mg intakes from 100·4 to 124·3 g/d while Mg absorption expressed as a proportion of intake was not significantly different for Mg intakes ranging from 64·6 to 124·3 g/d. Mg concentrations in rumen fluid after feeding increased (P<0·001) with increasing Mg intakes. Apparent absorption of Mg appeared to become saturated at a ruminal Mg concentration of 17·5 mM (Mg intake of 83·5 g/d). Group-mean post-feeding concentrations of Mg and Na in rumen fluid were significantly correlated (Pearson's r=−0·96; P=0·003, n=6). This study showed that under conditions of practical dairy cow feeding, Mg absorption was maximal at Mg intakes [ges ]84 g/d.

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