scholarly journals Relative contributions of the slippage and tunneling mechanisms to anion net efflux from human erythrocytes.

1984 ◽  
Vol 84 (6) ◽  
pp. 877-893 ◽  
Author(s):  
O Fröhlich
Keyword(s):  
Membrane Potential ◽  
Conformational Change ◽  
Chemical Nature ◽  
Human Erythrocytes ◽  
Alternative Process ◽  
Anion Transporter ◽  
Transport Site ◽  
Cl Conductance ◽  
Channel Type

The rates of anion net efflux from gramicidin-treated erythrocytes in the presence of a K gradient were measured at 25 degrees C, pH 7.8, as rates of loss of Ki. The experiments served to estimate the relative contributions of two hypothetical mechanisms to Cl net efflux at low extracellular Cl concentrations. Cl, Br, and NO3 net effluxes were measured into media of different Cl, Br, or NO3 concentrations, respectively, to determine and compare the relative rates of the extracellular anion-inhibitable components. They were 48, 160, and 230 mmol/(kg Hb X min), respectively, at a membrane potential of about -90 mV. This indicates that the anion-inhibitable efflux is not due solely to the return translocation of the empty transport site ("slippage") because slippage should be independent of the chemical nature of the anion. Cl net efflux was also measured as a function of the intracellular Cl concentration into media containing either 0 or 50 mM Cl. Under both conditions, net efflux was linearly dependent on Cli between 30 and 300 mM Cli and was 0 when back-extrapolated to 0 Cli. This observation is not compatible with the slippage process, which under these conditions would have been expected to be independent of Cli above 15 mM Cli. It was concluded that slippage contributes negligibly to Cl net efflux even at low extracellular anion concentrations and that the alternative process of "tunneling"--that is, movement of the anion through the anion transporter without a conformational change in a channel-type behavior--is the major, if not the sole, mechanism underlying Cl conductance.

Interactions of inhibitors on anion transporter of human erythrocyte

1987 ◽  
Vol 252 (2) ◽  
pp. C153-C162 ◽  
Author(s):  
O. Frohlich ◽  
R. B. Gunn
Keyword(s):  
Binding Site ◽  
Human Erythrocyte ◽  
Binding Domain ◽  
Human Erythrocytes ◽  
Anion Binding ◽  
Chloride Binding ◽  
Protein Surface ◽  
Anion Transporter ◽  
Transport Site ◽  
Chloride Concentrations

Chloride tracer efflux was measured from intact human erythrocytes into media containing different chloride concentrations and different concentrations of the inhibitors 4,4'-dinitrostilbene-2-2'-disulfonate (DNDS), N-(4-azido-2-nitrophenyl)-2-aminoethylsulfonate (NAP-taurine), phloretin, and sulfate. The data were analyzed to test whether these inhibitors were mutually exclusive with each other or whether they could bind at the same time. Under the assumption that mutual exclusiveness is due to steric interference, the data can be used to map out the protein surface near the outward-facing anion binding-transport site. It is concluded that there are separate domains for NAP taurine and phloretin that do not overlap with each other or with the chloride binding site. These two domains do, however, overlap with the binding domain for DNDS that, in addition, excludes the binding of chloride and sulfate.

Effect of low chloride on relaxation in hamster diaphragm muscle

1986 ◽  
Vol 61 (1) ◽  
pp. 180-184 ◽  
Author(s):  
S. A. Esau ◽  
N. Sperelakis
Keyword(s):  
Membrane Potential ◽  
Muscle Fatigue ◽  
Time Constant ◽  
Diaphragm Muscle ◽  
Resting Membrane Potential ◽  
Krebs Solution ◽  
Sarcolemmal Membrane ◽  
Cl Conductance

With muscle fatigue the chloride (Cl-) conductance of the sarcolemmal membrane decreases. The role of lowered Cl- conductance in the prolongation of relaxation seen with fatigue was studied in isolated hamster diaphragm strips. The muscles were studied in either a Krebs solution or a low Cl- solution in which half of the NaCl was replaced by Na-gluconate. Short tetanic contractions were produced by a 160-ms train of 0.2-ms pulses at 60 Hz from which tension (T) and the time constant of relaxation were measured. Resting membrane potential (Em) was measured using KCl-filled microelectrodes with resistances of 15–20 M omega. Mild fatigue (20% fall in tension) was induced by 24–25 tetanic contractions at the rate of 2/s. There was no difference in Em or T in the two solutions, either initially or with fatigue. The time constant of relaxation was greater in low Cl- solution, both initially (22 +/- 3 vs. 18 +/- 5 ms, mean +/- SD, P less than 0.05) and with fatigue (51 +/- 18 vs. 26 +/- 7 ms, P less than 0.005). Lowering of sarcolemmal membrane Cl- conductance appears to play a role in the slowing of relaxation of hamster diaphragm muscle seen with fatigue.

Nature of taurodehydrocholic acid uptake in rat hepatocytes

1988 ◽  
Vol 254 (2) ◽  
pp. G269-G274 ◽  
Author(s):  
W. G. Hardison ◽  
P. J. Lowe ◽  
E. Gosink
Keyword(s):  
Membrane Potential ◽  
Rat Hepatocytes ◽  
Competitive Inhibitor ◽  
Acid Uptake ◽  
Isolated Rat Hepatocytes ◽  
Acid Analogue ◽  
Sodium Gradient ◽  
Sodium Dependent ◽  
Independent Process ◽  
Transport Site

We studied uptake into isolated rat hepatocytes of the bile acid analogue taurodehydrocholate (TDHC) over a concentration range of 2.5-4,000 microM. Uptake was mainly by a saturable sodium-dependent process with a Km of approximately 50 microM and a Vmax of 0.036 nmol.s-1.mg protein-1. A lesser sodium-independent process was evident but was linear in the range studied. Both processes were inhibited by incubation at 37 degrees C under nitrogen in the presence of 3 mM sodium cyanide or by incubation at 0 degrees C. A single transport site was suggested by the Eadie-Hofstee plot of TDHC uptake from 2.5 to 750 microM. TDHC was a weak competitive inhibitor of taurocholic acid (TCA) uptake (Ki = 236 microM) but was not itself taken up by the TCA transport site. TCA exhibited moderately potent mixed inhibition of TDHC uptake. Uptake of both compounds was strongly inhibited by bromosulfophthalein (BSP) and Rose Bengal, whereas 0.5 mM alanine uptake was not affected. BSP exhibited a complex pattern of inhibition of TDHC uptake: mixed partial inhibition. Degree of inhibition of both TDHC and TCA uptake did not increase as BSP concentrations were increased from 50 to 100 microM. BSP did not exert its inhibitory effects by alteration of membrane potential or sodium gradients; 50 microM BSP changed membrane potential less than 10% and sodium gradient not at all. The data indicate that despite close structural analogy between TDHC and TCA, the two compounds are taken up by different sodium-dependent mechanisms. Nonetheless, the similar qualitative and quantitative effects of BSP on their uptakes suggests the mechanisms are related.

scholarly journals Anion-sensitive sodium conductance in the apical membrane of toad urinary bladder.

1980 ◽  
Vol 76 (1) ◽  
pp. 69-81 ◽  
Author(s):  
J Narvarte ◽  
A L Finn
Keyword(s):  
Membrane Potential ◽  
Urinary Bladder ◽  
Apical Membrane ◽  
Basolateral Membrane ◽  
Membrane Potentials ◽  
Toad Urinary Bladder ◽  
Bladder Epithelium ◽  
Anionic Composition ◽  
Before And After ◽  
Cl Conductance

Membrane potentials and the electrical resistance of the cell membranes and the shunt pathway of toad urinary bladder epithelium were measured using microelectrode techniques. These measurements were used to compute the equivalent electromotive forces (EMF) at both cell borders before and after reductions in mucosal Cl- concentration ([Cl]m). The effects of reduction in [Cl]m depended on the anionic substitute. Gluconate or sulfate substitutions increased transepithelial resistance, depolarized membrane potentials and EMF at both cell borders, and decreased cell conductance. Iodide substitutions had opposite effects. Gluconate or sulfate substitutions decreased apical Na conductance, where iodide replacements increased it. When gluconate or sulfate substitutions were brought about the presence of amiloride in the mucosal solution, apical membrane potential and EMF hyperpolarized with no significant changes in basolateral membrane potential or EMF. It is concluded that: (a) apical Na conductance depends, in part, on the anionic composition of the mucosal solution, (b) there is a Cl- conductance in the apical membrane, and (c) the electrical communication between apical and basolateral membranes previously described is mediated by changes in the size of the cell Na pool, most likely by a change in sodium activity.

A quantum mechanical Interaction of human erythrocytes

1982 ◽  
Vol 60 (1) ◽  
pp. 52-59 ◽  
Author(s):  
S. Rowlands ◽  
L. S. Sewchand ◽  
E. G. Enns
Keyword(s):  
Brownian Motion ◽  
Membrane Potential ◽  
Vibrational Mode ◽  
Human Erythrocytes ◽  
Metabolic Energy ◽  
Quantum Mechanical ◽  
Mechanical Interaction ◽  
Macromolecular Transport ◽  
Enzyme Substrate ◽  
Normal Human

Theory predicts that the membrane potential will polarize membrane molecules and cause them to vibrate coherently at a frequency of ~ 1011 Hz. If the supply of metabolic energy exceeds a minimum value, membrane phonons may condense their momentum into a single "giant" vibrational mode. At 1011 Hz ionic screening is small up to distances of approximately a micrometre, so forces of a range several orders of magnitude longer than chemical forces can arise. These forces may be attractive or repulsive depending on frequency. They should occur in every metabolically active membrane and may control macromolecular transport and enzyme–substrate interactions. We find that normal human erythrocytes in plasma form rouleaux faster than Brownian motion predicts. When cells are fixed in glutaraldehyde or are metabolically depleted, or if the membrane potential is brought to zero, the rate of aggregation agrees with Brownian theory. When the metabolically depleted cells are revived or if the membrane potential is restored, then the interaction returns.

Cl(-)-dependent NH4+ transport mechanisms in medullary thick ascending limb cells

1994 ◽  
Vol 267 (6) ◽  
pp. C1607-C1615 ◽  
Author(s):  
H. Amlal ◽  
M. Paillard ◽  
M. Bichara
Keyword(s):  
Membrane Potential ◽  
Intracellular Ph ◽  
Media Exposure ◽  
Thick Ascending Limb ◽  
Transport Mechanisms ◽  
K Channels ◽  
Initial Cell ◽  
Medullary Thick Ascending Limb ◽  
Free Media ◽  
Cl Conductance

To characterize Cl(-)-dependent NH4+ transport mechanisms in renal medullary thick ascending limb (MTAL), intracellular pH (pHi) and membrane potential (PD) were monitored with use of 2',7'-bis(carboxyethyl)- 5(6)-carboxyfluorescein and 3,3'-dipropylthiadicarbocyanine, respectively, in suspensions of rat MTAL tubules in CO2-free media. Exposure of MTAL cells to 4 mM NH4Br caused, after an initial cell alkalinization due to NH3 entry, an NH4(+)-induced fall in pHi that was approximately 67% less pronounced in Cl(-)-free than in Cl(-)-containing media. The following experiments were performed in the presence of 1 microM amiloride to block the MTAL NH4+ conductance. When cells were preincubated in a Cl(-)-free gluconate medium in which K+ and Cl- conductances are greatly reduced, abrupt addition of 100 mN N-methyl-D-glucamine (NMDG)-Cl had no effect on cell PD and pHi in the absence of ammonia, but acutely acidified the cells by approximately 0.2 pH units in the presence of 4 mM NH4Br, which thus indicated nonelectrogenic (NMDG-Cl)-dependent NH4+ influx. The latter also occurred in a Cl(-)-free thiocyanate medium in which the Cl- conductance was blocked by 0.1 mM diphenylamine-2-carboxylate (DPC). An NMDG-Cl- dependent NH4(+)-induced fall in pHi was reduced approximately 33% by 10 mM Ba+, approximately 84% by 0.1 mM bumetanide, and 100% by 1.5 mM furosemide, whereas 1 mM hydrochlorothiazide had no effect; inhibition by Ba+ was observed even in the presence of 0.1 mM verapamil added to block both K+ channels and K+/NH4+ antiport.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals In-silico Exploration of Channel Type and Efflux Silicon Transporters and Silicification Proteins in 80 Sequenced Viridiplantae Genomes

Plants ◽  
2020 ◽  
Vol 9 (11) ◽  
pp. 1612
Author(s):  
Muhammad Amjad Nawaz ◽  
Farrukh Azeem ◽  
Alexander Mikhailovich Zakharenko ◽  
Xiao Lin ◽  
Rana Muhammad Atif ◽  
...  
Keyword(s):  
Plant Species ◽  
In Silico ◽  
Structural Integrity ◽  
Green Plant ◽  
Rich Domain ◽  
Anion Transporter ◽  
Transporter Family ◽  
Gene Structures ◽  
Almost All ◽  
Channel Type

Silicon (Si) accumulation protects plants from biotic and abiotic stresses. It is transported and distributed within the plant body through a cooperative system of channel type (e.g., OsLsi1) and efflux (Lsi2s e.g., OsLsi2) Si transporters (SITs) that belong to Noduline-26 like intrinsic protein family of aquaporins and an uncharacterized anion transporter family, respectively. Si is deposited in plant tissues as phytoliths and the process is known as biosilicification but the knowledge about the proteins involved in this process is limited. In the present study, we explored channel type SITs and Lsi2s, and siliplant1 protein (Slp1) in 80 green plant species. We found 80 channel type SITs and 133 Lsi2s. The channel type SITs characterized by the presence of two NPA motifs, GSGR or STAR selectivity filter, and 108 amino acids between two NPA motifs were absent from Chlorophytes, while Streptophytes evolved two different types of channel type SITs with different selectivity filters. Both channel type SITs and Lsi2s evolved two types of gene structures each, however, Lsi2s are ancient and were also found in Chlorophyta. Homologs of Slp1 (225) were present in almost all Streptophytes regardless of their Si accumulation capacity. In Si accumulator plant species, the Slp1s were characterized by the presence of H, D-rich domain, P, K, E-rich domain, and P, T, Y-rich domain, while moderate Si accumulators lacked H, D-rich domain and P, T, Y-rich domains. The digital expression analysis and coexpression networks highlighted the role of channel type and Lsi2s, and how Slp1 homologs were ameliorating plants’ ability to withstand different stresses by co-expressing with genes related to structural integrity and signaling. Together, the in-silico exploration made in this study increases our knowledge of the process of biosilicification in plants.

Sign in / Sign up

Export Citation Format

Share Document