scholarly journals The role of potassium transport in the generation of a pH gradient in Escherichia coli

1981 ◽  
Vol 198 (3) ◽  
pp. 691-698 ◽  
Author(s):  
R G Kroll ◽  
I R Booth
Keyword(s):  
Escherichia Coli ◽  
Membrane Potential ◽  
Respiratory Rate ◽  
Potassium Transport ◽  
Ph Gradient ◽  
Simple Relationship ◽  
K Uptake ◽  
Net Uptake ◽  
K Transport

The role of K+ transport in the generation of a pH gradient in Escherichia coli has been investigated. In K+-depleted cells, net K+ uptake dissipated delta psi (membrane potential) and led to an increase in delta pH (pH gradient). The magnitude of the delta pH formed bore a simple relationship to the net K+ uptake and was substantially independent of the respiratory rate. In K+-replete cells, generation of a pH gradient was again K+-dependent, although no net uptake of this cation occurred. The results are discussed in terms of K+ cycling, and it is suggested that delta pH is in part a function of the rate of cycling and independent of the respiratory rate.

scholarly journals The relationship between intracellular pH, the pH gradient and potassium transport in Escherichia coli

1983 ◽  
Vol 216 (3) ◽  
pp. 709-716 ◽  
Author(s):  
R G Kroll ◽  
I R Booth
Keyword(s):  
Escherichia Coli ◽  
Intracellular Ph ◽  
Feedback Regulation ◽  
Potassium Transport ◽  
Potassium Uptake ◽  
Ph Gradient ◽  
Limited Capacity ◽  
E Coli ◽  
The Relationship ◽  
K Transport

The capacity of E. coli cells to regulate intracellular pH (pHi) during net potassium uptake has been investigated. The data show: (a) that cells sense their intracellular pH; (b) that the pH gradient (delta pH) exerts a feedback regulation on pHi; (c) that a mechanism of regulation of pHi exists which may be independent of Na+ [Zilberstein, Agmon, Schuldiner & Padan (1982) J. Biol. Chem. 257, 3687-3691]; and (d) that cells have a limited capacity to raise their intracellular pH in the absence of net K+ transport.

Hepatic production and intestinal uptake of IGF-I: response to infection

1998 ◽  
Vol 275 (6) ◽  
pp. G1291-G1298 ◽  
Author(s):  
Charles H. Lang ◽  
Robert A. Frost ◽  
Joseph Ejiofor ◽  
D. Brooks Lacy ◽  
Owen P. McGuinness
Keyword(s):  
Escherichia Coli ◽  
Nutrient Intake ◽  
Plasma Cortisol ◽  
Fibrin Clot ◽  
Intestinal Uptake ◽  
Doppler Flow ◽  
Factor I ◽  
Igf I ◽  
Net Uptake

The role of the liver and gut in contributing to the infection-induced fall in circulating insulin-like growth factor I (IGF-I) was examined in chronically catheterized conscious dogs. Two weeks before study, catheters and Doppler flow probes were implanted to assess hepatic and gut balance of IGF-I. To control nutrient intake, dogs were placed on total parenteral nutrition (TPN) as their sole caloric source. After dogs received TPN for 5 days, net hepatic and intestine IGF-I balances were assessed. A hypermetabolic infected state was then induced by the intraperitoneal implantation of a fibrin clot containing Escherichia coli. TPN was continued, and organ IGF-I balance was assessed 24 and 48 h after induction of infection. Arterial IGF-I levels were significantly decreased following infection (111 ± 18, 62 ± 10, and 63 ± 8 ng/ml before and 24 and 48 h after, respectively). Net hepatic IGF-I output decreased markedly (221 ± 73, to 73 ± 41 and 41 ± 17 ng ⋅ kg−1 ⋅ min−1before and 24 and 48 h after, respectively). The infection-induced decrease in hepatic IGF-I output could not be explained by concomitant alterations in plasma cortisol or insulin levels. The gut demonstrated a net uptake of IGF-I before infection (178 ± 29 ng ⋅ kg−1 ⋅ min−1). However, after infection, intestinal IGF-I uptake was completely suppressed (−10 ± 15 and −8 ± 36 ng ⋅ kg−1 ⋅ min−1). In summary, infection decreases net hepatic IGF-I release 65–80% and completely suppresses net IGF-I uptake by the intestine. As a consequence of these reciprocal changes in IGF-I balance across the liver and intestine, splanchnic production of IGF-I was unchanged by infection. These data suggest that changes in the clearance and/or production of IGF-I by extrasplanchnic tissues contribute to the infection-induced decrease in circulating IGF-I levels.

Cell volume regulation by skate erythrocytes: role of potassium

1990 ◽  
Vol 258 (5) ◽  
pp. R1217-R1223 ◽  
Author(s):  
K. G. Dickman ◽  
L. Goldstein
Keyword(s):  
Cell Volume ◽  
Phorbol Ester ◽  
Volume Regulation ◽  
Regulatory Volume Decrease ◽  
Cell Volume Regulation ◽  
Disulfonic Acid ◽  
Ionophore A23187 ◽  
K Uptake ◽  
K Transport

The role of K transport during cell volume regulation in response to extracellular osmolality, protein kinase C activation, and cellular Ca was examined in skate (Raja erinacea) red blood cells (RBC). Reduction of medium osmolality from 960 to 660 mosmol/kgH2O had no effect on K uptake or efflux despite a 25% increase in cell volume. Further reduction to 460 mosmol/kgH2O caused K uptake to double and K efflux to triple resulting in net K loss. Net K efflux in 460 mosmol/kgH2O medium was correlated with the presence of a regulatory volume decrease, which was sensitive to the anion transport inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) and insensitive to chloride replacement. K-K exchange was absent in both isotonic and hypotonic media. Treatment with the Ca ionophore A23187 in the presence of Ca had no effect on either cell volume or K efflux in isotonic medium, indicating the absence of Ca-activated K transport. In contrast, phorbol ester treatment caused cell volume, Na content, and proton and K efflux to increase. Consistent with activation of Na-H exchange, phorbol ester effects were inhibited by dimethylamiloride. This study constitutes the first demonstration of volume-sensitive K transport in RBC from the most primitive vertebrate studied to date.

scholarly journals The use of valinomycin, nigericin and trichlorocarbanilide in control of the protonmotive force in Escherichia coli cells

1983 ◽  
Vol 212 (1) ◽  
pp. 105-112 ◽  
Author(s):  
S Ahmed ◽  
I R Booth
Keyword(s):  
Escherichia Coli ◽  
Membrane Potential ◽  
Mode Of Action ◽  
Ph Gradient ◽  
Protonmotive Force ◽  
Modes Of Action ◽  
Escherichia Coli Cells ◽  
Low Concentrations ◽  
High K ◽  
Specific Control

Valinomycin, nigericin and trichlorocarbanilide were assessed for their ability to control the protonmotive force in Escherichia coli cells. Valinomycin, at high K+ concentrations, was found to decrease the membrane potential delta phi and indirectly to decrease the pH gradient delta pH. Nigericin was found to have two modes of action. At low concentrations (0.05-2 microM) it carried out K+/H+ exchange and decreased delta pH. At higher concentrations (50 microM) it carried out a K+-dependent transfer of H+, decreasing both delta phi and delta pH. In EDTA-treated cells only the latter mode of action was evident, whereas in a mutant sensitive to deoxycholate both types of effect were observed. Trichlorocarbanilide is proposed as an alternative to nigericin for the specific control of delta pH, and it can be used in cells not treated with EDTA.

scholarly journals Cation transport in Escherichia coli. IX. Regulation of K transport.

1978 ◽  
Vol 72 (3) ◽  
pp. 283-295 ◽  
Author(s):  
D B Rhoads ◽  
W Epstein
Keyword(s):  
Escherichia Coli ◽  
Steady State ◽  
Cation Transport ◽  
Transport Systems ◽  
Energy Requirements ◽  
Protonmotive Force ◽  
K Uptake ◽  
Kinetics Of ◽  
K Transport ◽  
External K

Kinetics of K exchange in the steady state and of net K uptake after osmotic upshock are reported for the four K transport systems of Escherichia coli: Kdp, TrkA, TrkD, and TrkF. Energy requirements for K exchange are reported for the Kdp and TrkA systems. For each system, kinetics of these two modes of K transport differ from those for net K uptake by K-depleted cells (Rhoads, D. B. F.B. Walters, and W. Epstein. 1976. J. Gen. Physiol. 67:325-341). The TrkA and TrkD systems are inhibited by high intracellular K, the TrkF system is stimulated by intracellular K, whereas the Kdp system is inhibited by external K when intracellular K is high. All four systems mediate net K uptake in response to osmotic upshock. Exchange by the Kdp and TrkA systems requires ATP but is not dependent on the protonmotive force. Energy requirements for the Kdp system are thus identical whether measured as net K uptake or K exchange, whereas the TrkA system differs in that it is dependent on the protonmotive force only for net K uptake. We suggest that in both the Kpd and TrkA systems formation of a phosphorylated intermediate is necessary for all K transport, although exchange transport may not consume energy. The protonmotive-force dependence of the TrkA system is interpreted as a regulatory influence, limiting this system to exchange except when the protonmotive force is high.

scholarly journals The effects of partial and selective reduction in the components of the proton-motive force on lactose uptake in Escherichia coli

1981 ◽  
Vol 200 (3) ◽  
pp. 583-589 ◽  
Author(s):  
S Ahmed ◽  
I R Booth
Keyword(s):  
Escherichia Coli ◽  
Steady State ◽  
Membrane Potential ◽  
Selective Reduction ◽  
Proton Motive Force ◽  
Motive Force ◽  
Ph Gradient ◽  
A Value ◽  
The Relationship ◽  
Lactose Transport

The relationship between the steady state lactose accumulation (delta plac) and the magnitude of the membrane potential (delta psi) and pH gradient (delta pH) has been studied at pHo5.5 and pHo7.5. An attempt has been made to differentiate between two possible means by which lactose accumulation may be reduced below the proton-motive force (delta p). Firstly, that delta psi and delta pH are not equivalent in driving lactose transport and secondly, that ‘slip’ reactions (beta-galactoside exit via the carrier without a proton) may reduce accumulation. The data support the latter; however, our conclusions are tempered by the observation that the apparent stoichiometry (delta plac/delta p) increases to a value of at least 2 at values of delta p below 130 mV.

scholarly journals Influence of Haemoglobin Conformation, Nitrite and Eicosanoids on K+ Transport Across the Carp Red Blood Cell Membrane

1992 ◽  
Vol 171 (1) ◽  
pp. 349-371 ◽  
Author(s):  
FRANK B. JENSEN
Keyword(s):  
Membrane Potential ◽  
Blood Cell ◽  
Red Blood Cell ◽  
Quaternary Structure ◽  
Large Fraction ◽  
Nordihydroguaiaretic Acid ◽  
K Uptake ◽  
Root Effect ◽  
T State ◽  
K Transport

The regulation of K+ transport across the red blood cell (RBC) membrane by haemoglobin (Hb) conformation was studied in carp, and the K+ transport mechanisms were identified. When a large proportion of Hb in the R quaternary structure was secured by oxygenation of blood at pH8.14, a net RBC K+ efflux was induced, which was accompanied by RBC shrinkage. This K+ efflux was resistant to ouabain and inhibited by furosemide and DIDS and by substitution of NO3− for Cl−, showing it to result from a K+/Cl− cotransport mechanism. Deoxygenation of the RBCs (Hb in T structure) eliminated the Cl−-dependent K+ efflux and resulted in a net K+ uptake via the Na+/K+ pump. These changes were fully reversible. Nitrite-induced methaemoglobin formation in deoxygenated blood, which converts a large fraction of the T structure Hb into an R-like conformation, shifted the K+ uptake to a Cl−-dependent K+ efflux similar to that seen in oxygenated cells. When the allosteric equilibrium between the R and T structures of Hb was gradually shifted towards the T state by decreases in pH, the Cl−-dependent K+ efflux from oxygenated cells decreased. At pH7.52, where the Root effect caused a potent stabilisation of the T state, the K+ efflux was reversed to a net K+ uptake. A similar change was induced in methaemoglobin-containing deoxygenated blood, since low pH also favours a T-like conformation of metHb. The variable K+ fluxes could not be related to changes in membrane potential or pH but were always directly related to the experimental modulation of the relative proportions of R- and T-structure Hb. It is proposed that Hb conformation governs K+ movements via a different binding of T and R structures to integral membrane proteins, and that a large fraction of R-structure Hb triggers the Cl−dependent K+ efflux mechanism. Application of inhibitors and a substrate of prostaglandin and leukotriene synthesis did not influence the K+ efflux from oxygenated erythrocytes. However, a fraction of the K+ efflux from nitrite-treated deoxygenated cells was inhibited by nordihydroguaiaretic acid, suggesting that a slightly larger K+ efflux from these RBCs than from oxygenated RBCs was related to leukotriene production caused by nitrite entry. A much larger influx of nitrite to deoxygenated than to oxygenated RBCs was positively correlated with the distribution ratio of H+ and the membrane potential, supporting the view that nitrite primarily enters the cells via conductive transport. The physiological implications of the results are discussed.

scholarly journals Dual Role for the Tyrosine Decarboxylation Pathway in Enterococcus faecium E17: Response to an Acid Challenge and Generation of a Proton Motive Force

2008 ◽  
Vol 75 (2) ◽  
pp. 345-352 ◽  
Author(s):  
C. I. Pereira ◽  
D. Matos ◽  
M. V. San Romão ◽  
M. T. Barreto Crespo
Keyword(s):  
Membrane Potential ◽  
Enterococcus Faecium ◽  
Proton Motive Force ◽  
Motive Force ◽  
Ph Gradient ◽  
Ph Homeostasis ◽  
Fermentation Products ◽  
Cell Counts ◽  
Acid Challenge

ABSTRACT In this work we investigated the role of the tyrosine decarboxylation pathway in the response of Enterococcus faecium E17 cells to an acid challenge. It was found that 91% of the cells were able to remain viable in the presence of tyrosine when they were incubated for 3 h in a complex medium at pH 2.5. This effect was shown to be related to the tyrosine decarboxylation pathway. Therefore, the role of tyrosine decarboxylation in pH homeostasis was studied. The membrane potential and pH gradient, the parameters that compose the proton motive force (PMF), were measured at different pHs (pH 4.5 to 7). We obtained evidence showing that the tyrosine decarboxylation pathway generates a PMF composed of a pH gradient formed due to proton consumption in the decarboxylation reaction and by a membrane potential which results from electrogenic transport of tyrosine in exchange for the corresponding biogenic amine tyramine. The properties of the tyrosine transporter were also studied in this work by using whole cells and right-side-out vesicles. The results showed that the transporter catalyzes homologous tyrosine/tyrosine antiport, as well as electrogenic heterologous tyrosine-tyramine exchange. The tyrosine transporter had properties of a typical precursor-product exchanger operating in a proton motive decarboxylation pathway. Therefore, the tyrosine decarboxylation pathway contributes to an acid response mechanism in E. faecium E17. This decarboxylation pathway gives the strain a competitive advantage in nutrient-depleted conditions, as well as in harsh acidic environments, and a better chance of survival, which contributes to higher cell counts in food fermentation products.

scholarly journals Quantitative measurements of the proton-motive force and its relation to steady state lactose accumulation in Escherichia coli

1981 ◽  
Vol 200 (3) ◽  
pp. 573-581 ◽  
Author(s):  
S Ahmed ◽  
I R Booth
Keyword(s):  
Escherichia Coli ◽  
Steady State ◽  
Membrane Potential ◽  
Proton Motive Force ◽  
Motive Force ◽  
Ph Gradient ◽  
Experimental Conditions ◽  
Ph Values ◽  
Quantitative Measurements ◽  
Essential Prerequisite

The magnitude of delta psi (membrane potential), delta pH (pH gradient), lactose accumulation and cytoplasmic volume have been determined over a range of experimental conditions. A study of two probes of delta pH, benzoate and dimethyloxazolidene-2,4-dione (DMO), and four probes of delta psi, Rb+, K+, tetraphenylphosphonium (TPP+) and 3,3′-dipropylthiodicarbocyanine iodide, has been carried out. Benzoate and DMO are shown to be equivalent at pH values above the pK of DMO, but the latter may be less accurate below this pH. The cations TPP+ and Rb+ were found, by a number of criteria, to be equivalent, and TPP+ may be used in cells not pretreated with EDTA. These studies are an essential prerequisite to the use of TPP+ as a quantitative probe in untreated cells.

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