scholarly journals The concentration of glycine by preparations of the yeast Saccharomyces Carlsbergensis depleted of adenosine triphosphate: Effects of proton gradients and uncoupling agents

1976 ◽  
Vol 154 (3) ◽  
pp. 669-676 ◽  
Author(s):  
A Seaston ◽  
G Carr ◽  
A. A Eddy
Keyword(s):  
Membrane Potential ◽  
Intracellular Ph ◽  
Adenosine Triphosphate ◽  
Proton Conductors ◽  
Equivalent Amount ◽  
Accumulation Ratio ◽  
Proton Gradients ◽  
Glycine Uptake ◽  
Proton Symport ◽  
Low Rate

1. At pH 4.5 and 30degreesC, yeast preparations depleted of ATP in the presence of antimycin and deoxyglucose spontaneously lost K+, gaining roughly an equivalent amount of H+. 2. Five proton conductors including azide and 2,4-dinitrophenol accelerated this process, as did [14C]glycine, which was absorbed with two extra equivalents of H+. 3. The rate of glycine uptake at pH 4.5 diminished fourfold when cellular K+ fell by 20%. 4. The distribution of [14C]propionate indicated that the intracellular pH fell from 6.2 to 5.7 when the cellular content of K+ fell by 30%. 5. Glycine uptake from a 5 muM solution was about 400 times faster at pH 4.5 than it was at pH 7.4 with 100mM-KCl present ostensibly to lower the membrane potential. 6. Yeast preparations containing 2mM-[14C]glycine absorbed a further amount from a 0.1 muM solution at pH 4.5. After about 10 min a net movement of [14C]glycine out of the yeast occurred. The ratio of the cellular [14Ia1glycine concentration to the concentration outside the yeast reached 4 × 104 in these assays, whereas at pH 7.4 in the presence of 100mM-KCl it did not exceed 15 in 3h. Dimitrophenol lowered the accumulation ratio at pH 4.5, apparently by causing proton conduction. 7. The observations are consistent with the notion that glycine uptake is driven by a proton symport mechanism. 8. Possible factors governing the strikingly low rate of glycine efflux as opposed to its optimum rate of influx are discussed.

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 Cytoplasmic [Ca2+] and intracellular pH in lymphocytes. Role of membrane potential and volume-activated Na+/H+ exchange.

1987 ◽  
Vol 89 (2) ◽  
pp. 185-213 ◽  
Author(s):  
S Grinstein ◽  
S Cohen
Keyword(s):  
Protein Kinase C ◽  
Membrane Potential ◽  
Protein Kinase ◽  
Intracellular Ph ◽  
Enzyme Treatment ◽  
Membrane Hyperpolarization ◽  
Kinase C ◽  
Free Media ◽  
Stimulation Of

The effect of elevating cytoplasmic Ca2+ [( Ca2+]i) on the intracellular pH (pHi) of thymic lymphocytes was investigated. In Na+-containing media, treatment of the cells with ionomycin, a divalent cation ionophore, induced a moderate cytoplasmic alkalinization. In the presence of amiloride or in Na+-free media, an acidification was observed. This acidification is at least partly due to H+ (equivalent) uptake in response to membrane hyperpolarization since: it was enhanced by pretreatment with conductive protonophores, it could be mimicked by valinomycin, and it was decreased by depolarization with K+ or gramicidin. In addition, activation of metabolic H+ production also contributes to the acidification. The alkalinization is due to Na+/H+ exchange inasmuch as it is Na+ dependent, amiloride sensitive, and accompanied by H+ efflux and net Na+ gain. A shift in the pHi dependence underlies the activation of the antiport. The effect of [Ca2+]i on Na+/H+ exchange was not associated with redistribution of protein kinase C and was also observed in cells previously depleted of this enzyme. Treatment with ionomycin induced significant cell shrinking. Prevention of shrinking largely eliminated the activation of the antiport. Moreover, a comparable shrinking produced by hypertonic media also activated the antiport. It is concluded that stimulation of Na+/H+ exchange by elevation of [Ca2+]i is due, at least in part, to cell shrinking and does not require stimulation of protein kinase C.

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.

High affinity L-aspartate transport in chick small intestine

1987 ◽  
Vol 252 (1) ◽  
pp. C105-C114 ◽  
Author(s):  
T. G. Wingrove ◽  
G. A. Kimmich
Keyword(s):  
Small Intestine ◽  
Membrane Potential ◽  
Epithelial Cells ◽  
Intracellular Ph ◽  
Transport Function ◽  
Flux Enhancement ◽  
High Affinity ◽  
Absolute Requirement ◽  
Potential Sensitivity ◽  
In Cells

Epithelial cells isolated from chick small intestine were used to study the mechanism of L-aspartate transport. Two kinetically distinct uptake systems of high (Km' = 16 microM) and low (Km'' = 2.7 mM) affinity are observed. This paper examines the cation dependence and membrane potential sensitivity of the high affinity system. Unidirectional influx studies indicate that extracellular Na+ is an absolute requirement for transport function. Flux is optimal when K+ is present intracellularly, however this cation is not required for Na+-dependent L-aspartate uptake. In the absence of K+, flux enhancement is observed when the intracellular pH is acidic. In contrast, acidic intracellular pH is inhibitory in cells that are preequilibrated with K+. Sodium ([Na+]o greater than [Na+]i gradients, and potassium ([K+]o less than [K+]i) or proton ([H+]o less than [H+]i) gradients can independently energize the Na+-dependent accumulation of L-aspartate above equilibrium levels, suggesting that Na+ and L-aspartate cotransport occurs with concomitant K+ or H+ antiport. L-Aspartate influx is insensitive to membrane potential changes created by inwardly directed anion gradients in the presence or absence of intracellular K+. A model is presented that is consistent with electroneutral Na+-coupled transfer with an ion antiport site of low specificity.

Sign in / Sign up

Export Citation Format

Share Document