Extracellular acidification at the surface of depolarized voltage-clamped snail neurones detected with eccentric combination pH microelectrodes

1987 ◽  
Vol 65 (5) ◽  
pp. 1001-1005 ◽  
Author(s):  
R. C. Thomas
Keyword(s):  
Membrane Potential ◽  
Intracellular Ph ◽  
Extracellular Ph ◽  
Electrochemical Gradient ◽  
Extracellular Acidification ◽  
Surface Ph ◽  
Buffering Power ◽  
Snail Neurones ◽  
Series Of Experiments ◽  
Ph Microelectrodes

A new design of double micropipette was used to measure intracellular pH, membrane potential, and surface pH of superfused snail neurones. A third double micropipette was used to control the membrane potential via a CsCl-filled barrel and inject HCl iontophoretically. In one series of experiments the surface pH fell by up to one-third of a pH unit when the membrane potential was clamped to 20 mV, pHi was initially 6.7, and extracellular pH was about 7.4 in a medium buffered either with 2 mM HEPES or 2.7% CO2 and 20 mM bicarbonate. In a second series in which surface pH was observed during brief depolarizations to different potentials with different pHi, the potential at which the surface began to acidify varied with pHi with a slope of 32 mV per pH unit. The results confirm that H+ ions leave depolarized snail neurones if the electrochemical gradient is favourable and show that CO2–bicarbonate buffered solutions have a low effective extracellular buffering power for rapid additions of acid.

Ammonia movement and distribution after exercise across white muscle cell membranes in rainbow trout

1996 ◽  
Vol 271 (3) ◽  
pp. R738-R750 ◽  
Author(s):  
Y. Wang ◽  
G. J. Heigenhauser ◽  
C. M. Wood
Keyword(s):  
Membrane Potential ◽  
Cell Membrane ◽  
Intracellular Ph ◽  
Muscle Cell ◽  
Cell Membranes ◽  
White Muscle ◽  
Extracellular Ph ◽  
Posterior Portion ◽  
Arterial Inflow ◽  
Muscle Cell Membrane

Manipulations of pH and electrical gradients in a perfused preparation were used to analyze the factors controlling ammonia distribution and flux in trout white muscle after exercise. Trout were exercised to exhaustion, and then an isolated-perfused white muscle preparation with discrete arterial inflow and venous outflow was made from the posterior portion of the tail. The tail-trunks were perfused with low (7.4)-, medium (7.9)-, and high (8.4)-pH saline, achieved by varying HCO3- concentration ([HCO3-]) at constant Pco2. Intracellular and extracellular pH, ammonia, CO2, K+, Na+, and Cl- were measured. Muscle intracellular pH was not affected by changes in extracellular pH. Increasing extracellular pH caused a decrease in the transmembrane NH3 partial pressure (PNH3) gradient and a decrease in ammonia efflux. When extracellular K+ concentration was increased from 3.5 to 15 mM in the medium-pH group, a depolarization of the muscle cell membrane potential from -92 to -60 mV and a 0.1-unit depression in intracellular pH occurred. Ammonia efflux increased despite a marked reduction in the PNH3 gradient. Amiloride (10(-4) M) had no effect, indicating that Na+/H(+)-NH4+ exchange does not participate in ammonia transport in this system. A comparison of observed intracellular-to-extracellular ammonia distribution ratios with those modeled according to either pH or Nernst potential distributions supports a model in which ammonia distribution across white muscle cell membranes is affected by both pH and electrical gradients, indicating that the membranes are permeable to both NH3 and NH4+. Membrane potential, acting to retain high levels of NH4+ in the intracellular compartment, appears to have the dominant influence during the postexercise period. However, at rest, the pH gradient may be more important, resulting in much lower intracellular ammonia levels and distribution ratios. We speculate that the muscle cell membrane NH3-to-NH4+ permeability ratio in trout may change between the rest and postexercise condition.

scholarly journals Expression of the Genes Encoding the Trk and Kdp Potassium Transport Systems ofMycobacterium tuberculosisduring GrowthIn Vitro

2015 ◽  
Vol 2015 ◽  
pp. 1-11 ◽  
Author(s):  
Moloko C. Cholo ◽  
Elizabeth J. van Rensburg ◽  
Ayman G. Osman ◽  
Ronald Anderson
Keyword(s):  
Membrane Potential ◽  
Gene Knockout ◽  
Housekeeping Gene ◽  
Extracellular Ph ◽  
Transport Systems ◽  
Mrna Levels ◽  
Genes Encoding ◽  
Series Of Experiments ◽  
Encoding Genes ◽  
Intracellular Vacuole

Two potassium (K+)-uptake systems, Trk and Kdp, are operative inMycobacterium tuberculosis(Mtb), but the environmental factors triggering their expression have not been determined. The current study has evaluated the expression of these genes in theMtbwild-type and atrk-gene knockout strain at various stages of logarithmic growth in relation to extracellular K+concentrations and pH. In both strains, mRNA levels of the K+-uptake encoding genes were relatively low compared to those of the housekeeping gene,sigA, at the early- and mid-log phases, increasing during late-log. Increased gene expression coincided with decreased K+uptake in the context of a drop in extracellular pH and sustained high extracellular K+concentrations. In an additional series of experiments, the pH of the growth medium was manipulated by the addition of 1N HCl/NaOH. Decreasing the pH resulted in reductions in both membrane potential and K+uptake in the setting of significant induction of genes encoding both K+transporters. These observations are consistent with induction of the genes encoding the active K+transporters ofMtbas a strategy to compensate for loss of membrane potential-driven uptake of K+at low extracellular pH. Induction of these genes may promote survival in the acidic environments of the intracellular vacuole and granuloma.

Bioenergetics of membrane transport in Synechococcus R-2 (Anacystis nidulans, S.leopoliensis) PCC7942

1998 ◽  
Vol 76 (6) ◽  
pp. 1127-1145
Author(s):  
Raymond J Ritchie
Keyword(s):  
Membrane Potential ◽  
Intracellular Ph ◽  
Anacystis Nidulans ◽  
Transport Systems ◽  
Electrochemical Gradient ◽  
Accumulation Ratio ◽  
Electrogenic Transport ◽  
Wide Range ◽  
Transport Of Ions ◽  
Photosynthesis And Respiration

Specialized chemical probe techniques need to be used to measure the membrane potential (delta psii,o) or the intracellular pH (pHi) of the cyanobacterium Synechococcus R-2 (PCC7942). The pHi of Synechococcus is essentially a set point (7.3) over a wide range of extracellular pH (pHo) from 7 to 11. Maintenance of the pHo is strongly Na+-dependent and the cells cannot tolerate acid pHo. The 86Rb+-valinomycin method of measuring the delta psii,o has inherent limitations, the most obvious being that the valinomycin treatment itself might alter the membrane potential. 201Tl+ has been found in Synechococcus to distribute across the plasmalemma passively, and so the accumulation ratio of the ion ([Tl+]i/[Tl+]o or Tl+i,o) can be used to calculate the apparent delta psii,o. The two types of probe give comparable results in Synechococcus. Polarizations of the delta psii,o of cells, because of electrogenic transport of ions, can be detected from its effects upon the uptake rate of permeant cations using both the 86Rb+-valinomycin and 201Tl+ methods. HCO3- hyperpolarized delta psii,o, whereas NH4+, CH3NH3+, and K+ led to depolarization. Most active transport systems, including the HCO3- pump, in cyanophytes appear to be ATP binding cassette (ABC) type ATP pumps. Few cotransport (H+ or Na+) driven mechanisms have been identified. A substantial proportion of the power available from photosynthesis and respiration is used to maintain ionic gradients and the membrane potential and in the light a large part (10%) is used to import inorganic carbon.Key words: cyanobacteria, membrane potential, intracellular pH, electrochemical gradient, bioenergetics.

scholarly journals Intracellular pH-regulating mechanism of the squid axon. Relation between the external Na+ and HCO-3 dependences.

1985 ◽  
Vol 85 (3) ◽  
pp. 325-345 ◽  
Author(s):  
W F Boron
Keyword(s):  
Intracellular Ph ◽  
Recovery Rate ◽  
Ion Pair ◽  
Squid Axon ◽  
Extrusion Rate ◽  
Pair Model ◽  
Buffering Power ◽  
Series Of Experiments ◽  
Acid Extrusion ◽  
External Ph

The intracellular pH-regulating mechanism of the squid axon was examined for its dependence on the concentrations of external Na+ and HCO3-, always at an external pH (pHo) of 8.0. Axons having an initial intracellular pH (pHi) of approximately 7.4 were internally dialyzed with a solution of pH 6.5 that contained 400 mM Cl- and no Na+. After pHi had fallen to approximately 6.6, dialysis was halted, thereby returning control of pHi to the axon. With external Na+ and HCO-3 present, intracellular pH (pHi) increased because of the activity of the pHi-regulating system. The acid extrusion rate (i.e., equivalent efflux of H+, JH) is the product of the pHi recovery rate, intracellular buffering power, and the volume-to-surface ratio. The [HCO3-]o dependence of JH was examined at three fixed levels of [Na+]o: 425, 212, and 106 mM. In all three cases, the apparent Jmax was approximately 19 pmol X cm-2 X s-1. However, the apparent Km (HCO3-) was approximately inversely proportional to [Na+]o, rising from 2.6 to 5.4 to 9.7 mM as [Na+]o was lowered from 425 to 212 to 106 mM, respectively. The [Na+]o dependence of JH was similarly examined at three fixed levels of [HCO3-]o: 12, 6, and 3 mM. The Jmax values did not vary significantly from those in the first series of experiments. The apparent Km (Na+), however, was approximately inversely related to [HCO3-]o, rising from 71 to 174 to 261 mM as [HCO3-]o was lowered from 12 to 6 to 3 mM, respectively. These results agree with the predictions of the ion-pair model of acid extrusion, which has external Na+ and CO3= combining to form the ion pair NaCO3-, which then exchanges for internal Cl-. When the JH data are replotted as a function of [NaCO3-]o, data from all six groups of experiments fall along the same Michaelis-Menten curve, with an apparent Km (NaCO3-) of 80 microM. The ordered and random binding of Na+ and CO3= cannot be ruled out as possible models, but are restricted in allowable combinations of rate constants.

scholarly journals Transmembrane electrical potential and transmembrane pH gradient in the acidophile Thiobacillus ferro-oxidans

1979 ◽  
Vol 178 (1) ◽  
pp. 195-200 ◽  
Author(s):  
J C Cox ◽  
D G Nicholls ◽  
W J Ingledew
Keyword(s):  
Membrane Potential ◽  
Intracellular Ph ◽  
Co2 Fixation ◽  
Electrical Potential ◽  
Sole Source ◽  
Ph Gradient ◽  
Electrochemical Gradient ◽  
Transmembrane Electrical Potential ◽  
External Ph

Thiobacillus ferro-oxidans is capable of using the oxidation of Fe2+ by O2 at pH 2.0 as the sole source of energy for growth and CO2 fixation. The bacterium maintains an intracellular pH of 6.5 over a range of external pH from 1.0 to 8.0, as measured by [14C]acetate and [3H]methylamine distribution. The membrane potential was estimated by the distribution of the lipid-soluble cation dibenzyldimethylammonium and the anion SCN-. At pH 2.0 (the pH of growth) during Fe2+ oxidation the transmembrane pH gradient is 4.5 units with an opposing membrane potential of -10mV, giving a proton electrochemical gradient of +256mV. This gradient is actively maintained.

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