Steps in p-aminohippurate transport by kidney slices

1958 ◽  
Vol 196 (1) ◽  
pp. 86-92 ◽  
Author(s):  
Ernest C. Foulkes ◽  
Benjamin F. Miller
Keyword(s):  
Cell Membrane ◽  
Transport System ◽  
Rate Constants ◽  
Extracellular Space ◽  
Concentration Ratio ◽  
Tissue Concentration ◽  
The Other ◽  
Facilitated Diffusion ◽  
Tubular Lumen ◽  
Cortical Slices

The existence of two intracellular fractions of PAH was demonstrated in renal cortical slices of the rabbit on incubation with C14-labeled PAH. One of these fractions is rapidly diffusible and rapidly equilibrates with extracellular PAH. The other fraction, in contrast, diffuses and equilibrates slowly; it is responsible for the high slice to medium concentration ratio of PAH. On the basis of these results a model of the PAH transport system in slices is proposed. This consists of step I, the diffusion of PAH from the medium into the extracellular space in the tissue; there follows step II, a facilitated diffusion step at the peritubular cell membrane; within the cell step III builds up a high tissue concentration of PAH; finally step IV transfers PAH across the luminal border of the cell into the tubular lumen from which it may diffuse back into the medium. Experiments were designed in which each of these steps could be measured individually and their rate constants determined. Alteration of the value of these rate constants by specific drugs localizes the action of such compounds at the peritubular cell membrane (Benemid, 9-alphafluorohydrocortisone) or at the level of both steps II and III in the case of DNP, octanoate and Diodrast. An explanation is also offered for the effect of cold on PAH influx and efflux. It can be calculated that the contribution of step IV to the turnover of PAH in slices is not quantitatively significant.

scholarly journals Quantitative analysis of proton-linked transport system. β-Galactoside exit in Escherichia coli

1980 ◽  
Vol 188 (2) ◽  
pp. 467-473 ◽  
Author(s):  
I R Booth ◽  
W A Hamilton
Keyword(s):  
Escherichia Coli ◽  
Quantitative Analysis ◽  
Transport System ◽  
Rate Constants ◽  
The Other ◽  
First Order ◽  
First Order Kinetics ◽  
Solute Accumulation ◽  
External Ph

The exit of lactose and thiomethyl-beta-D-galactoside from Escherichia coli ML308-225 has been studied to determine the role of carrier-dependent (zero-trans efflux) and carrier-independent (leak) processes. On the basis of its sensitivity to p-chloromercuribenzene sulphonate the exit of lactose was found to be almost wholly mediated by the carrier. Consistent with this conclusion was the finding that the rate of exit of this sugar was dependent on the external pH, being considerably slower at acid pH. On the other hand exit of thiomethyl-beta-D-galactoside was found to be composed of both carrier-dependent and carrier-independent processes. Both processes exhibited first-order kinetics with the rate constants for zero-trans efflux and leak being 0.137 min-1 and 0.079 min-1, respectively. The relevance of these findings for out earlier proposal for the methods of attenuation of solute accumulation is discussed [Booth, Mitchell & Hamilton (1979) Biochem. J. 182, 687–696].

Methylene. III. Gas phase reactions with 1-chloropropane

1969 ◽  
Vol 312 (1509) ◽  
pp. 141-161 ◽  
Keyword(s):  
Gas Phase ◽  
Rate Constants ◽  
Hydrogen Abstraction ◽  
The Other ◽  
Gas Phase Reactions ◽  
Other Hand ◽  
Chlorine Substituent ◽  
High Degree ◽  
Singlet Methylene

The work described in this and the following paper is a continuation of that in parts I and II, devoted to elucidation of the mechanism of the reactions of methylene with chloroalkanes, with particular reference to the reactivities of singlet and triplet methylene in abstraction and insertion processes. The products of the reaction between methylene, prepared by the photolysis of ketene, and 1-chloropropane have been identified and estimated and their dependence on reactant pressures, photolysing wavelength and presence of foreign gases (oxygen and carbon mon­oxide) has been investigated. Both insertion and abstraction mechanisms contribute significantly to the over-all reaction, insertion being relatively much more important than with chloroethane. This type of process appears to be confined to singlet methylene. If, as seems likely, there is no insertion into C—Cl bonds under our conditions (see part IV), insertion into C2—H and C3—H bonds occurs in statistical ratio, approximately. On the other hand, the chlorine substituent reduces the probability of insertion into C—H bonds in its vicinity. As in the chloroethane system, both species of methylene show a high degree of selectivity in their abstraction reactions. We find that k S Cl / k S H >7.7, k T Cl / k T H < 0.14, where the k ’s are rate constants for abstraction, and the super- and subscripts indicate the species of methylene and the type of atom abstracted, respectively. Triplet methylene is discriminating in hydrogen abstraction from 1-C 3 H 7 Cl, the overall rates for atoms attached to C1, C2, C3 being in the ratios 2.63:1:0.

Numerical Simulation and Analysis of Compartment Fire in Subway Train

2012 ◽  
Vol 166-169 ◽  
pp. 2726-2730
Author(s):  
Bo Si Zhang ◽  
Shou Xiang Lu
Keyword(s):  
Numerical Simulation ◽  
Transport System ◽  
Fire Safety ◽  
Urban Transport ◽  
The Other ◽  
Compartment Fire ◽  
Fire Simulation ◽  
Subway Train ◽  
Simulation Time

Subway plays an important role in urban transport system. Fire as the major risk of the subway, is gaining increasing concern. In this study, fire simulation is performed to estimate fire safety of different compartments of the subway train. Result shows that the two compartments in the middle become dangerous at 150s and the compartments in the two ends are not safe at 300s approximately. The other two compartments are always safe during the simulation time.

Lead and calcium transport in human erythrocyte

1999 ◽  
Vol 18 (5) ◽  
pp. 327-332 ◽  
Author(s):  
J V Calderón-Salinas ◽  
M A Quintanar-Escorcia ◽  
M T González-Martínez ◽  
C E Hernández-Luna
Keyword(s):  
Transport System ◽  
Human Erythrocyte ◽  
Calcium Transport ◽  
Human Erythrocytes ◽  
The Other ◽  
Erythrocyte Ghosts ◽  
Passive Transport ◽  
Ca Uptake

In this paper we report the lead (Pb) and calcium (Ca) uptake by erythrocyte ghosts. In both cases the transport was carried out by a passive transport system with two kinetic components (Michaelis-Menten and Hill). Pb and Ca were capable of inhibiting the transport of the other metal in a non-competitive way. Under hyperpolarization, the uptakes of Ca and Pb were enhanced and the Michaelis-Menten component prevailed. Both Ca and Pb uptakes were inhibited by N-ethyl-maleimide to the same extent. These results indicate that Pb and Ca share the same permeability pathway in human erythrocytes and that this transport system is electrogenic.

scholarly journals The Relationships between Cholesterol and Suicide: An Update

2012 ◽  
Vol 2012 ◽  
pp. 1-6 ◽  
Author(s):  
Domenico De Berardis ◽  
Stefano Marini ◽  
Monica Piersanti ◽  
Marilde Cavuto ◽  
Giampaolo Perna ◽  
...  
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Cell Membrane ◽  
The Other ◽  
Core Component ◽  
Cell Membrane Stability ◽  
Cholesterol Levels ◽  
The Central Nervous System ◽  
Larger Sample

Cholesterol is a core component of the central nervous system, essential for the cell membrane stability and the correct functioning of neurotransmission. It has been observed that cholesterol may be somewhat associated with suicidal behaviours. Therefore, the aim of this paper was to elucidate current facts and views about the role of cholesterol levels in mood disorders. The majority of the studies reviewed in the present paper suggest an interesting relationship between cholesterol (especially lower levels) and suicidality. On the other hand, particularly during the last years, relationships between serum cholesterol and suicidality were doubted on the basis of some recent studies that have not found any correlation. However, the debate on relationships between cholesterol and suicide is open and longitudinal studies on a larger sample of patients are needed to further clarify this important issue.

Rotary movements and fluid membranes in termite flagellates

1976 ◽  
Vol 20 (3) ◽  
pp. 619-638
Author(s):  
S.L. Tamm ◽  
S. Tamm
Keyword(s):  
Plasma Membrane ◽  
Comparative Analysis ◽  
Cell Membrane ◽  
Shear Zone ◽  
Surrounding Medium ◽  
The Other ◽  
Visual Evidence ◽  
Fluid Membranes ◽  
Internal Motor ◽  
Rotary Motor

We previously described a remarkable type of cell motility that provided direct, visual evidence for the fluid nature of cell membranes. The movement involved continual, unidirectional rotation of one part of a protozoan, including the plasma membrane and cytoplasmic organelles, in relation to a neighbouring part. The cell membrane in the ‘shear zone’ appeared continuous with that of the rest of the cell. The rotary motor consisted, at least in part, of a non-contractile, microtubular axostyle which extended centrally through the cell. The protozoan was a devescovinid flagellate found in the hindgut of a Florida termite. In this paper, we have confirmed earlier reports of this type of motility in other kinds of devescovinids from Australian termites. By demonstrating continuity of the plasma membrane in the shear zone of the Australian devescovinids as well, we have obtained additional examples that provide direct, visual evidence for fluid membranes. A comparative analysis of rotational motility in various devescovinids revealed 2 different kinds of rotary mechanisms. Hyperdevescovina probably have an internal motor, in which one part of the cell exerts forces against another part, as in the Florida termite devescovinid. Devescovina species, on the other hand, have an external motor, in which flagellar and/or papillar movements exert forces against the surrounding medium. The structure of the axostyle in different devescovinids was compared, and its role in rotational motility discussed with respect to the behavioural data.

Pulsatile urea excretion in gulf toadfish (Opsanus beta): evidence for activation of a specific facilitated diffusion transport system.

1998 ◽  
Vol 201 (6) ◽  
pp. 805-817 ◽  
Author(s):  
C M Wood ◽  
K M Gilmour ◽  
S F Perry ◽  
P Part ◽  
P J Walsh
Keyword(s):  
Transport System ◽  
Transport Mechanism ◽  
Sea Water ◽  
Facilitated Diffusion ◽  
Urea Transporter ◽  
Diffusion Transport ◽  
Peg 4000 ◽  
Net Uptake ◽  
Bidirectional Transport ◽  
External Water

When toadfish are made ureotelic by a crowding/confinement protocol, they excrete approximately 90 % of their urea nitrogen (urea-N) production in large, irregular pulses (1-2 pulses per day) from the gill region. We investigated three hypotheses as to the mechanism of pulsatile excretion: (i) the presence of an active reabsorptive 'back-transport' mechanism that is periodically inhibited to allow urea-N excretion to occur; (ii) the periodic occurrence of a generalized, non-specific increase in gill permeability; and (iii) the presence of a specific facilitated diffusion transport system that is periodically activated. Exposure of toadfish during non-pulse periods to treatments designed to block a 'back-transport' mechanism (Na+-free sea water or the urea analogues 30 mmol l-1 thiourea or 30 mmol l-1 acetamide in the external water) did not stimulate a leakage of urea-N, thereby opposing the first hypothesis. The second hypothesis was opposed by several results. Neither injection of the potent branchial vasodilator L-isoprenaline (10(-5) mol l-1) nor infusion of NH4Cl, the latter at levels known to stimulate urea-N efflux in perfused gills, had any effect on urea-N excretion. Furthermore, during natural pulse events, when the normally very low gill permeability to urea (3x10(-7) cm s-1) increased at least 35-fold, there was no accompanying increase in permeability to either 3H2O (1.5x10(-5) cm s-1) or the paracellular marker [14C]PEG-4000 (10(-8) cm s-1). However [14C]thiourea permeability (1.5x10(-7) cm s-1) increased approximately fivefold, in support of the third hypothesis. Furthermore, when 30 mmol l-1 urea was placed in the external water, a concentration (60 000 micromol-N l-1) approximately three times that of blood (20 000 micromol-N l-1), each efflux pulse event (measured with [14C]urea) was accompanied by a net uptake, such that blood urea-N levels rose rather than fell. A proportional 1:1 relationship between influx per unit external concentration and efflux per unit internal (i.e. plasma) concentration indicated a fully bidirectional transport system. The simultaneous presence of 60 mmol l-1 thiourea in the external water inhibited the influx component by 73 %, further supporting this conclusion. These data, together with recent molecular, morphological and endocrinological evidence, strongly suggest that pulsatile urea-N excretion is caused by the periodic activation of a facilitated urea transporter in the gills, similar to the vasopressin-regulated urea transporter in the mammalian kidney.

Ketoconazole - an antifungal drug for oral use

1981 ◽  
Vol 19 (23) ◽  
pp. 91-92
Keyword(s):  
Antifungal Activity ◽  
Cell Membrane ◽  
Oral Administration ◽  
Antifungal Agent ◽  
Systemic Effect ◽  
Antifungal Drug ◽  
The Other ◽  
Membrane Synthesis ◽  
Fungal Cell

Ketoconazole (Nizoral - Janssen) is a new antifungal agent. Like the other imidazoles with antifungal activity such as miconazole,1 clotrimazole2 and econazole,3 it acts by inhibiting fungal cell-membrane synthesis.4 It is well absorbed and exerts a systemic effect; it is thus suitable for oral administration.

Stop-flow analysis applied to the excretion of hemoglobin

1960 ◽  
Vol 199 (2) ◽  
pp. 292-294 ◽  
Author(s):  
C. L. Malmendier ◽  
J. P. DeKoster ◽  
F. Vander Veiken ◽  
H. Brauman ◽  
M. DeMyttenaere ◽  
...  
Keyword(s):  
Flow Analysis ◽  
Middle Part ◽  
The Other ◽  
Physiological Data ◽  
Sodium Reabsorption ◽  
Water Reabsorption ◽  
Tubular Lumen ◽  
Influence Of Water ◽  
Stop Flow ◽  
Ureteral Occlusion

The stop-flow analysis has been applied to the study of the excretion of hemoglobin, in order to compare the physiological data with the morphological views. The study of the ratio U/P hemoglobin/U/P creatinine suggests that this protein penetrates the tubular lumen by diffusion during the ureteral occlusion and progressed slowly under influence of water reabsorption. During this migration, hemoglobin undergoes the effects of a double reabsorption: one in the middle part of the proximal convoluted tubule, the other more distally situated in a zone not distinguishable from the site of sodium reabsorption.

Energetics of sugar transport by isolated intestinal epithelial cells: effects of cytochalasin B

1979 ◽  
Vol 237 (1) ◽  
pp. C56-C63 ◽  
Author(s):  
G. A. Kimmich ◽  
J. Randles
Keyword(s):  
Steady State ◽  
Epithelial Cells ◽  
Transport System ◽  
Cytochalasin B ◽  
Intestinal Epithelial Cells ◽  
Sugar Accumulation ◽  
Facilitated Diffusion ◽  
Intestinal Epithelial ◽  
Passive System ◽  
Concentration Gradients

The capability of isolated intestinal epithelial cells to establish concentration gradients of 3-O-methylglucose (3-OMG) by a Na+-dependent transport system is limited by concomitant function of a Na+-independent, facilitated diffusion transport system. Monosaccharides accumulated by the active system are continuously lost via the passive system, which acts to lower steady-state sugar gradients maintained by the cell. Cytochalasin B is a potent inhibitor of the passive system and allows the cells to establish a sugar gradient that is much higher than normal. When extracellular [3-;OMG] is 1 mM, cytochalasin induces sugar accumulation ratios of 30-;fold (+/- phlorizin) in contrast to control ratios of approximately 10-;fold. When [3-;OMG] is 0.1 mM, cytochalasin (0.1 mM) induces 40-;fold accumulation ratios. When changes in extracellular sugar concentration are considered, steady-state concentration gradients observed are 70-;fold. For a Na:sugar coupling stoichiometry of 1:1, gradients of this magnitude represent the approximate theoretical maximum for a transport system driven exclusively by the transmembrane electrochemical potential for Na+.

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