scholarly journals Exploring an ‘ideal hill': how lithology and transport mechanisms affect the possibility of a steady state during weathering and erosion

2020 ◽  
Vol 45 (3) ◽  
pp. 652-665 ◽  
Author(s):  
Marina I. Lebedeva ◽  
Susan L. Brantley
Keyword(s):  
Steady State ◽  
Transport Mechanisms

The anterior and posterior ‘stomach’ regions of larval Aedes aegypti midgut: regional specialization of ion transport and stimulation by 5-hydroxytryptamine

1999 ◽  
Vol 202 (3) ◽  
pp. 247-252 ◽  
Author(s):  
T.M. Clark ◽  
A. Koch ◽  
D.F. Moffett
Keyword(s):  
Steady State ◽  
Aedes Aegypti ◽  
Ion Transport ◽  
Malpighian Tubules ◽  
Transport Mechanisms ◽  
Regional Specialization ◽  
Negative Deflection ◽  
Electrical Polarity

The ‘stomach’ region of the larval mosquito midgut is divided into histologically distinct anterior and posterior regions. Anterior stomach perfused symmetrically with saline in vitro had an initial transepithelial potential (TEP) of −66 mV (lumen negative) that decayed within 10–15 min to a steady-state TEP near −10 mV that was maintained for at least 1 h. Lumen-positive TEPs were never observed in the anterior stomach. The initial TEP of the perfused posterior stomach was opposite in polarity, but similar in magnitude, to that of the anterior stomach, measuring +75 mV (lumen positive). This initial TEP of the posterior stomach decayed rapidly at first, then more slowly, eventually reversing the electrical polarity of the epithelium as lumen-negative TEPs were recorded in all preparations within 70 min. Nanomolar concentrations of the biogenic amine 5-hydroxytryptamine (5-HT, serotonin) stimulated both regions, causing a negative deflection of the TEP of the anterior stomach and a positive deflection of the TEP of the posterior stomach. Phorbol 12,13-diacetate also caused a negative deflection of the TEP of the anterior stomach, but had no effect on the TEP of the posterior stomach. These data demonstrate that 5-HT stimulates region-specific ion-transport mechanisms in the stomach of Aedes aegypti and suggest that 5-HT coordinates the actions of the Malpighian tubules and midgut in the maintenance of an appropriate hemolymph composition in vivo.

Groundwater Colloid Properties and their Potential Influence on Radionuclide Transport

1996 ◽  
Vol 465 ◽  
Author(s):  
C. Degueldre
Keyword(s):  
Steady State ◽  
Water Flow Rate ◽  
Clay Fraction ◽  
Radionuclide Transport ◽  
Transport Mechanisms ◽  
Transport Models ◽  
Contaminated Aquifer ◽  
Suspension Process ◽  
Alkali Elements ◽  
Respective Concentration

ABSTRACTColloid facilitated transport is still an issue in radioactive waste management. Sophisticated phenomenological transport models are available, but progress is required to fully understand mechanisms and parameters. This study lead in this direction. Investigation of the marl groundwater colloids in steady-state conditions at Wellenberg, shows that their concentration is independent of the water flow rate. Their generation is caused by the re-suspension of the rock clay fraction only. The re-suspension process is presently being studied under flow transient conditions. Extension of our measurements to other safety relevant systems as well as a literature survey show that the colloid concentration under steady-state conditions is correlated to the concentration of alkali elements and earth alkali elements. The higher their respective concentration, the fewer colloids are occurring. Considerations on colloid contamination models are also included. The paper emphasises various colloid transport mechanisms including colloid generation from the irreversibly contaminated aquifer.

Steady State and Transient Photoconductivity of Thin Film Polydiacetylene Single Crystals

1990 ◽  
Vol 214 ◽  
Author(s):  
Y. Yang ◽  
J. Y. Lee ◽  
P. Miller ◽  
L. Li ◽  
J. Kumar ◽  
...  
Keyword(s):  
Thin Film ◽  
Steady State ◽  
Single Crystals ◽  
Drift Velocity ◽  
Incident Light ◽  
Light Polarization ◽  
Transport Mechanisms ◽  
Carrier Generation ◽  
Electric Field Dependence ◽  
Transient Photoconductivity

ABSTRACTCharge carrier generation and transport mechanisms in polydiacetylene thin film single crystals., poly-PTS (2,4-hexadiyne-1,6-diol bis(p-toluenesulfonate)) and poly- BTFP (bis-(4-n-butyl-2,3,5,6-tetra-fluorophenyl) butadiyne), are studied by using steady state and transient photoconductivity techniques. The electric field dependence of the steady state photocurrent is superlinear for both samples. Dependence of photocurrent on incident light polarization has been investigated. The polarization dependence of photocurrent has completely different behavior for the polydiacetylene PTS and BTFP. Single-gap transmission line experiment has been designed to directly measure the drift velocity of PTS single crystals. A drift velocity of the order of 106cm/s was measured.

Acidification of three types of liver endocytic vesicles: similarities and differences

1994 ◽  
Vol 266 (1) ◽  
pp. C81-C94 ◽  
Author(s):  
R. W. Van Dyke ◽  
J. D. Belcher
Keyword(s):  
Steady State ◽  
Chloride Concentration ◽  
Multivesicular Bodies ◽  
Receptor Recycling ◽  
Transport Mechanisms ◽  
Proton Efflux ◽  
Vesicle Membrane ◽  
Chloride Medium ◽  
Three Stages ◽  
Endocytic Vesicles

Endocytosed ligands move through a series of progressively more acidic vesicles. These differences in pH (pHi) could reflect differences in ion transport mechanisms. Vesicles representing three stages of endocytosis, compartment for uncoupling of receptor and ligand (CURL), multivesicular bodies (MVB), and receptor recycling compartment (RRC), were studied, and all exhibited ATP-dependent electrogenic acidification that was a saturable function of medium chloride. Initial rates of acidification differed (RRC > CURL > MVB), and proton influx was similar for CURL and RRC but slower for MVB. Steady-state ATP-dependent pHi in the three vesicles was more similar. Vesicle membrane potential was substantial (+41 to +69 mV) in low-chloride medium and greatest for RRC but was low (-6 to +6 mV) in 140 mM KCl. These vesicles also exhibited -22 to -37 mV Donnan potentials. Steady-state pump-generated proton electrochemical gradients (delta mu H+) ranged from 114 to 175 mV and were greater for CURL and RRC than for MVB; however, delta mu H+ changed little over a 140-fold difference in chloride concentration. Proton leak rates were faster in CURL and RRC than in MVB, but proton efflux was similar. Finally, proton fluxes and permeabilities, calculated with regard to surface area, differed in the opposite direction (MVB > CURL > RRC). Thus, for the endocytic vesicles studied, intrinsic differences in proton flux and in vesicle geometry could be demonstrated that contributed to differences in pre-steady-state vesicle pHi.

scholarly journals Theoretical effects of transmembrane electroneutral exchange on membrane potential.

1984 ◽  
Vol 83 (1) ◽  
pp. 47-56 ◽  
Author(s):  
R Jacob ◽  
D Piwnica-Worms ◽  
C R Horres ◽  
M Lieberman
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Reversal Potential ◽  
Cell Types ◽  
Transport Mechanisms ◽  
Ionic Concentrations

Transmembrane electroneutral transport mechanisms [e.g., Na/H exchange, Cl/HCO3 exchange, (K + Cl) cotransport] have recently been identified in a wide variety of cell types. If these exchanges sum to give a net electroneutral Na/K exchange, they may hyperpolarize the membrane potential beyond the value calculated from the Mullins-Noda equation, provided the cell maintains steady state intracellular ionic concentrations. In extreme circumstances, the membrane potential could hyperpolarize beyond the potassium reversal potential. This effect is mediated by the electrogenic Na/K pump. If either Na or K exchanges electroneutrally against a third ion (e.g., Na/Ca exchange), then the exchange may depolarize the membrane potential.

scholarly journals The temperature dependence of the adrenergic Na+/H+ exchanger of trout erythrocytes

1990 ◽  
Vol 148 (1) ◽  
pp. 303-312 ◽  
Author(s):  
A. R. Cossins ◽  
R. V. Kilbey
Keyword(s):  
Steady State ◽  
Rainbow Trout ◽  
Temperature Dependence ◽  
Effect Of Temperature ◽  
Transport Mechanisms ◽  
Adrenergic Stimulation ◽  
Temperature Dependent ◽  
Effects Of Temperature ◽  
Time Required

The effects of temperature upon the adrenergic Na+/H+ exchange of rainbow trout erythrocytes have been studied in vitro. The initial rates of H+ ejection and of increase of intracellular Na+ [(Na+]i) in adrenergically stimulated cells were highly temperature-dependent, with apparent Arrhenius activation energies of 112.8 +/− 10.0 (mean +/− S.D., N = 4) and 84.1 +/− 3.0 kJ mol-1 (N = 3), respectively. The steady-state [Na+]i following stimulation decreased progressively with cooling, whilst the time required for [Na+]i to return to control values after removal of agonist was greatly increased. The change in intracellular pH resulting from adrenergic stimulation was reduced by cooling, such that at 4 degrees C adrenergic responses were barely measurable. The effect of temperature upon the steady-state [Na+]i and pHi was probably caused by a disparity in the temperature dependence of the transport mechanisms that contribute to the respective steady states.

scholarly journals Loss-of-function and gain-of-function phenotypes of stomatocytosis mutant RhAG F65S

2011 ◽  
Vol 301 (6) ◽  
pp. C1325-C1343 ◽  
Author(s):  
Andrew K. Stewart ◽  
Boris E. Shmukler ◽  
David H. Vandorpe ◽  
Alicia Rivera ◽  
John F. Heneghan ◽  
...  
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Xenopus Oocytes ◽  
Cellular Responses ◽  
Transport Mechanisms ◽  
Loss Of Function ◽  
Wild Type ◽  
Gain Of Function ◽  
Cation Conductance ◽  
Methylammonium Chloride

Four patients with overhydrated cation leak stomatocytosis (OHSt) exhibited the heterozygous RhAG missense mutation F65S. OHSt erythrocytes were osmotically fragile, with elevated Na and decreased K contents and increased cation channel-like activity. Xenopus oocytes expressing wild-type RhAG and RhAG F65S exhibited increased ouabain and bumetanide-resistant uptake of Li+and86Rb+, with secondarily increased86Rb+influx sensitive to ouabain and to bumetanide. Increased RhAG-associated14C-methylammonium (MA) influx was severely reduced in RhAG F65S-expressing oocytes. RhAG-associated influxes of Li+,86Rb+, and14C-MA were pharmacologically distinct, and Li+uptakes associated with RhAG and RhAG F65S were differentially inhibited by NH4+and Gd3+. RhAG-expressing oocytes were acidified and depolarized by 5 mM bath NH3/NH4+, but alkalinized and depolarized by subsequent bath exposure to 5 mM methylammonium chloride (MA/MA+). RhAG F65S-expressing oocytes exhibited near-wild-type responses to NH4Cl, but MA/MA+elicited attenuated alkalinization and strong hyperpolarization. Expression of RhAG or RhAG F65S increased steady-state cation currents unaltered by bath Li+substitution or bath addition of 5 mM NH4Cl or MA/MA+. These oocyte studies suggest that 1) RhAG expression increases oocyte transport of NH3/NH4+and MA/MA+; 2) RhAG F65S exhibits gain-of-function phenotypes of increased cation conductance/permeability, and loss-of-function phenotypes of decreased and modified MA/MA+transport, and decreased NH3/NH4+-associated depolarization; and 3) RhAG transports NH3/NH4+and MA/MA+by distinct mechanisms, and/or the substrates elicit distinct cellular responses. Thus, RhAG F65S is a loss-of-function mutation for amine transport. The altered oocyte intracellular pH, membrane potential, and currents associated with RhAG or RhAG F65S expression may reflect distinct transport mechanisms.

Regulation of pH in rat brain synaptosomes. II. Role of Cl-

1994 ◽  
Vol 71 (6) ◽  
pp. 2249-2257 ◽  
Author(s):  
R. Martinez-Zaguilan ◽  
R. J. Gillies ◽  
S. Sanchez-Armass
Keyword(s):  
Steady State ◽  
Rat Brain ◽  
Initial Rate ◽  
Ringer Solution ◽  
Disulfonic Acid ◽  
Transport Mechanisms ◽  
Rat Brain Synaptosomes ◽  
Brain Synaptosomes ◽  
Acid Loading

1. We have previously shown that rat brain synaptosomes exhibit a very dynamic Na+/H+ exchanger. We have also observed that although synaptosomes lack HCO3(-)-based transport mechanisms, they do respond with changes in pHi upon Clo- removal. 2. Here we show that when synaptosomes are transferred from Ringer solution (RS) to Cl(-)-free RS, there is a cytosolic alkalinization of approximately 0.22 pH units. This phenomenon is DIDS (4,4'-diisothiocyanostilbene-3,3'-disulfonic acid) inhibitable. The alkalinization is completely reversed when Cl- ions are reintroduced. The presence of HCO3- or Ca2+ does not modify the response to Cl(-)-removal or replenishment. 3. In acid-loading experiments, the initial rate of pHi recovery is higher in Cl(-)-free RS than in RS. The final resting pHi after the recovery in Cl(-)-free RS is approximately 0.22 pH units higher than that obtained in media containing Cl-. The magnitude of the NaOAc-induced acidification is 2.5-fold larger in the presence than in the absence of Cl-. Similar results are obtained in the presence of HCO3-. 4. These data suggest that H+ movements may be coupled to Cl- movements. To study this possibility further, we developed a technique to simultaneously measure H+ and Cl- by using the fluorescence of 5' (and 6')-carboxy-10-dimethylamino-3-hydroxy-spyro-[7H benzo[c]xanthene- 7,1'(3'H)-isobenzofuran]3'-one (SNARF-1) and MQAE [N-(6-methoxyquinolyl)acetoxy ester], respectively. 5. Our results indicated that the steady-state [Cl-]i in synaptosomes is approximately 56 mM, thus indicating that Cli- is not passively distributed.(ABSTRACT TRUNCATED AT 250 WORDS)

Neutral and DEAE dextrans as tracers for assessing lung microvascular barrier permeability and integrity

2002 ◽  
Vol 93 (1) ◽  
pp. 251-262 ◽  
Author(s):  
Jonathan R. Sanders ◽  
N. Adrienne Pou ◽  
Robert J. Roselli
Keyword(s):  
High Performance Liquid Chromatography ◽  
Liquid Chromatography ◽  
Steady State ◽  
High Performance ◽  
Capillary Permeability ◽  
Transport Mechanisms ◽  
Pulmonary Capillary ◽  
Before And After ◽  
Endogenous Proteins ◽  
Lung Lymph

Steady-state lymph-to-plasma concentration ratios (L/Ps) of neutral dextrans, cationic DEAE dextrans, and endogenous proteins were determined under normal and increased permeability conditions in six unanesthetized yearling sheep prepared with chronic lung lymph fistulas. Fluorescent dextrans with radii ranging from 1 to 30 nm were intravenously infused, and after 24 h, perilla ketone (PK) was given to alter permeability while the dextran infusion was maintained. Plasma and lymph samples were collected before and after PK administration and analyzed for dextran and protein concentrations after high-performance liquid chromatography size separation. Under both baseline and increased permeability conditions, DEAE dextrans had higher L/Ps than neutral dextrans of similar size but lower L/Ps than proteins of similar size. Comparison of L/Ps before and after PK revealed that the percentage change in permeability for neutral and DEAE dextrans was significantly larger than that for proteins. These results suggest that 1) the pulmonary microvascular barrier behaves as a net negative barrier, 2) some transport mechanisms for proteins and dextrans are different, and 3) neutral and cationic dextrans are more sensitive markers than proteins of the same size for assessing changes in pulmonary capillary permeability.

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