Potassium transport in the Ehrlich mouse ascites tumor cell: evidence for autoinhibition by external potassium

The membrane potential of Ehrlich ascites tumor cells microelectrode measurements and their critical evaluation

Intracellular potentials were measured, using a piezoelectric electromechanical transducer to impale Ehrlich ascites tumor cells with capillary microelectrodes. In sodium Ringer's, the potential immediately after the penetration was -24±7 mV, and decayed to a stable value of about -8 mV within a few msec. The peak potentials disappeared in potassium Ringer's and reappeared immediately after resuspension in sodium. Ringer's, whereas the stable potentials were only slightly influenced by the change of medium. The peak potential is in good agreement with the Nernst potential for chloride. This is also the case when cell sodium and potassium have been changed by addition of ouabain. It is concluded that the peak potentials represent the membrane potential of the unperturbed cell, and that chloride is in electrochemical equilibrium across the cell membrane.The membrane potential of about -11 mV previously reported corresponds to the stable potential in this study, and is considered as a junction potential between damaged cells and their environment. Similar potential differences were recorded between a homogenate of cells and Ringer's.The apparent membrane resistance of Ehrlich cells was about 70 Ωcm(2). This is two orders of magnitude less than the value calculated from(36)Cl fluxes, and may, in part, represent a leak in the cell membrane.For comparison, the influence of an eventual leak on measurements in red cells and mitochondria is discussed.

A cooperative transition theory applied to the kinetics of ionic exchanges in cells

Manifestations of a cooperative interaction between ion-adsorbing sites in cells include steep, sigmoidal equilibrium adsorption isotherms of K+ and Na+, critical temperature transitions of net exchanges of Na+ for K+, and the allosteric nature of the effects of ligands on cellular K+ and Na+. Cooperative ionic adsorption is described by a one-dimensional Ising model. The experimentally-determined equilibrium parameters permit prediction of the kinetics of exchange of K+ for Na+ (the approach to equilibrium) by stochastic or hydrodynamic solutions of a time-dependent Ising model. Studies of the rates of self-exchange of adsorbed ions reveal properties of the cooperatively interacting adsorption sites and their dependence on temperature and chemical potential. High rates of isotopic exchanges of K+ and Na+ occur near the transition point. This is explained by the hypothesis of an increase in susceptibility of the ensemble to slight variations of microK or microNA near the phase transition, which leads to an increase in microscopic fluctuations within the ensemble. It is suggested that the isotopic ion exchange experiment may be a means to explore the microscopic states of the ensemble and their transition probabilities.

Incorporation of phospholipids in Ehrlich ascites tumor cells

Ehrlich ascites tumor cells (EATC) were incubated with unilamellar vesicles (UV) or multilamellar vesicles (MV). UV and MV were incorporated differently into EATC. The increase in 32P-phospholipid in EATC in the presence of UV was 12% in 300 min. Absorption of phospholipid from MV could account for only 3%. About 50% of the UV incorporation of 32P was by endocytosis and/or fusion.

Specific drug sensitive transport pathways for chloride and potassium ions in steady-state Ehrlich mouse ascites tumor cells

A major aim of this investigation was to determine whether, in steady-state ascites cells, Cl- transport can be partitioned into a furosemide-sensitive cotransport with K+ and a separate 4,4'-isothiocyanostilbene-2,2'-disulfonic acid (DIDS) sensitive self-exchange. Both Cl- and K+ fluxes were studied. The furosemide- and Cl- sensitive K+ fluxes were equivalent, both in normal ionic media and when the external K+ concentration, [K+]o, was varied from 4 to 30 mM. The stoichiometry of the furosemide-sensitive Cl- and K+ fluxes was 2 Cl-:1 K+ at 0.1 and 0.5 mM drug levels but increased to 3 Cl-:1 K+ at 1.0 mM furosemide. DIDS at 0.1 mM had no effect on the K+ exchange rate but inhibited Cl- exchange by 39% +/- 2 (S.E.). The effects of DIDS and 0.5 mM furosemide on Cl- transport were additive but 1.0 mM furosemide and DIDS had overlapping inhibitory actions. Thus furosemide acts on components of K+ and Cl- transport which are linked to each other, but the drug also inhibits an additional DIDS-sensitive Cl- pathway, when present at higher concentrations. The dependence of the furosemide-sensitive K+ and Cl- transport on [K+]o was also studied; both fluxes fell as the [K+]o increased. The latter results recall those in an earlier study by Hempling (Hempling, H.G. (1962) J. Cell. Comp. Physiol. 60, 181-198).

Multiple fractions of sodium exchange in human lymphocytes

Human lymphocytes contain a large, saturable fraction of K+ that exchanges slowly with K+ in the external medium, and a small non-saturable fraction that exchanges rapidly. We determined whether or not Na+ exchanges in a similar manner with external Na+. Cells were pre-equilibrated to ensure absence of net ion movements. Efflux was studied by loading with 22Na and transferring without washing to a non-labeled medium. Influx was studied by transferring to labeled medium and separating large samples of cells at 6,000g. There are fast, intermediate, and slow fractions of Na+ exchange, with half-times of 2, 14, and 120 minutes. At normal external K+, most cells Na+ exchanges rapidly, while at lower external K+ the Na+ that replaces cell K+ exchanges slowly. Parellel sources of fast and slow fractions, such as extracellular ones and subpopulations of cells, were ruled out by simultaneous 42K and 22Na fluxes and by a quantitative analysis of the combined K+ and Na+ content and flux data over a range of external K+ and Na+ levels. Five possible models of ion fluxes occurring in series were considered. Surface matrix, surface binding sites, and cytoplasmic channels with rapid nuclear exchange were eliminated as sources of the fast fractions. Therefore, the fast fractions of K+ and Na+ must reflect the permeability of the surface membrane. This left only two possible sources of the slow fractions. One, a subcellular compartment (e.g., nucleus), was eliminated by the combined content and flux data. We conclude that the slow fractions of ion flux are rate-limited by adsorption onto and desorption from cellular macromolecules. The data support the association-induction hypothesis and are understood by reference to two fundamental concepts: that of rapid solute exclusion from cell water existing in a polarized state; and that of solute accumulation limited by adsorption onto fixed anionic sites within the cell.

Effects of bilirubin on potassium (86Rb+) influx and ionic content in Ehrlich ascites cells

Potassium influx, intracellular potassium and sodium content and cellular volume were determined in vitro in Ehrlich ascites cells in the presence of up to 0.8 mM bilirubin in the incubation medium. Bilirubin uptake into cells as a function of bilirubin concentration in the incubation medium increased linearly with a molar bilirubin/albumin ratio of 20 : 1. Potassium influx and intracellular content decreased while cellular volume increased after 180 min of incubation of cells in bilirubin at a molar bilirubin/albumin ratio of 20 : 1. At a bilirubin/albumin ratio 2 : 1, potassium influx decreased, cellular volume remained unchanged, and bilirubin uptake into cells became saturated at bilirubin concentrations greater than 0.3 mM. It is suggested that bilirubin-induced alterations in potassium gradients across cell membranes may play a role in toxic effects of bilirubin on cells.

Fast and slow fractions of K+ flux in human lymphocytes

Potassium influx and efflux were studied in human peripheral blood lymphocytes equilibrated over a wide range of external K+ levels. The absence of a net ion movement throughout the flux study was established, trapped space was measured with polyethylene glycol, and cells were separated from incubation media without exposure to any washing solution. There are both rapid and slow cellular fractions of 42K influx and efflux, and half-times of exchange of around 2 minutes, and 400 minutes, respectively. The rapid component is identical in magnitude to the smaller non-saturable component of cell K+, while the slow component is identified with the larger, sigmoidal, saturable component of cell K+ that was previously shown to follow a cooperative adsorption isotherm. These results support the association-induction hypothesis, which predicts (a) a rapid fraction of K+ flux due to equilibration of ion within cell water existing in a state of polarized multilayers, and (b) a slower component of K+ flux limited by adsorption onto, or desorption from, fixed anionic sites existing throughout the cell. K+ influx, as a function of external K+, showed a triphasic relation with a peak around 1 mM K+ex, then a trough around 4mM K+ex, and then a gradual rise. This relation was readily explained, in terms of the association-induction hypothesis, by the cooperative interaction between, and ion occupancy of, fixed anionic sites that adsorb K+ or Na+.

The membrane potential of mouse ascites-tumour cells studied with the fluorescent probe 3,3'-dipropyloxadicarbocyanine. Amplitude of the depolarization caused by amino acids

1. The magnitude of the K+ gradient across the plasma membrane, which was in equilibrium with the membrane potential (E) of the tumour cells, was determined by the "null point" procedure of Hoffman & Laris (1974) [J. Physiol. (London) 239, 519--552] in which the fluorescence of the dye serves as an indicator of changes in the magnitude of E. 2. A mixture of oligomycin, 2,4-dinitrophenol and antimycin was used to stop the mitochondria from interfering with the fluorescence signal. Transport functions at the plasmalemma were maintained under these conditions in the presence of glucose. 3. Physiological circumstances were found in which incubation with glycine or with glucose changed the "null point" value of E within the range--20mV to--100mV. The fluorescence intensity at the "null point" was an approximately linear function of E over that range. The procedure enabled E to be inferred form the fluorescence intensity in circumstances where titration to the "null point" was not feasible. 4. The rapid depolarization caused by l-methionine or glycine was shown in this way to have a maximum amplitude of about 60mV. A mathematical model of this process was devised. 5. The electrogenic Na+ pump hyperpolarized the cells up to about --80mV when the cellular and extracellular concentrations of K+ were roughly equal. 6. The observations show that the factors generating the membrane potential represent a major source of energy available for the transport of amino acids in this system.

Loss of inorganic ions from host cells infected with Chlamydia psittaci

Mouse fibroblasts (L cells) infected with the 6BC strain of Chlamydia psittaci released potassium ion (K(+)) into the extracellular milieu in a way that depended on size of inoculum and time after infection. When the multiplicity of infection was 500 to 1,000 50% infectious units (ID(50)) per L cell, loss of intracellular K(+) was first apparent 4 to 10 h after infection and was nearly complete at 6 to 20 h. Magnesium ion and inorganic phosphate (P(i)) were also released. Similar multiplicities of ultraviolet-inactivated C. psittaci also caused release of K(+). Leakage of inorganic ions probably resulted from immediate damage to the host-cell plasma membrane during ingestion of large numbers of chlamydiae. With multiplicities of 1 to 50 ID(50) per L cell, ingestion of C. psittaci was not by itself enough to cause release of K(+) and P(i) from infected L cells. There was a delay of 36 to 72 h between infection and massive leakage of intracellular ions during which time the chlamydiae multiplied extensively. Fifty ID(50) of ultraviolet-inactivated C. psittaci per L cell did not bring about significant leakage of K(+), even after 72 h. The mechanism whereby these multiplicities of infection destroy the ability of host cells to retain intracellular molecules is not known. HeLa 229 cells also released K(+) and P(i) after infection, but these losses occurred more slowly than in comparably infected L cells, possibly because C. psittaci did not multiply as extensively in HeLa cells as it did in L cells. The significance of the inability of chlamydiae-infected cells to regulate the flow of molecules through their plasma membranes is discussed.

Intracellular compartmentation of Na+, K+ and Cl- in the Ehrlich ascites tumor cell: correlation with the membrane potential

The intracellular distribution of Na+, K+, Cl- and water has been studied in the Ehrlich ascites tumor cell. Comparison of the ion and water contents of whole cells with those of cells exposed to La3+ and mechanical stress indicated that La3+ treatment results in selective damage to the cell membrane and permits evaluation of cytoplasmic and nuclear ion concentrations. The results show that Na+ is sequestered within the nucleus, while K+ and Cl- are more highly concentrated in the cell cytoplasm. Reduction of the [Na+] of the incubation medium by replacement with K+ results in reduced cytoplasmic [Na+], increased [Cl-] and no change in [K+]. Nuclear concentrations of these ions are virtually insensitive to the cation composition of the medium. Concomitant measurements of the membrane potential were made. The potential in control cells was -13.7 mV. Reduction of [Na+] in the medium caused significant depolarization. The measured potential is describable by the Cl- equilibrium potential and can be accounted for in terms of cation distributions and permeabilities. The energetic implications of the intracellular compartmentation of ions are discussed.

Monitoring membrane potentials in Ehrlich ascites tumor cells by means of a fluorescent dye

1. The fluorescent intensity of the dye 3,3'-dipropylthiodicarbocyanine iodide was measured in suspensions of Ehrlich ascites tumor cells in an attempt to monitor their membrane potentials under a variety of different ionic and metabolic conditions. 2. In the presence of valinomycin, fluorescent intensity is dependent on log [K+]medium (the fluorescent intensity increased with increasing [K+]medium) where K+ replaced Na+ in the medium. Cellular K+ content also influenced fluorescent intensity in the presence of valinomycin. With lower cellular K+, fluorescent intensity in the presence of valinomycin for any given concentration was increased. 3. In the presence of gramicidin fluorescent intensity was highest in Krebs-Ringer and decreased with the substitution of choline+ for Na+. 4. The observations with ionophores are consistent with the hypothesis that the dye monitors membrane potential in these cells with an increase in fluorescence indicating membrane depolarization (internal becomes more positive). 5. The estimated membrane potentials were influenced by the way in which the cells were treated. Upon dilution of the cells from 1 in 20 to 1 in 300 the initial estimations were between -50 and -60 mV. With incubation at 1 in 300 dilution for 1 h at room temperature or a 37 degrees C, the membrane potentials ranged from -18 to -42 mV. 6. Estimations of membrane potential on the basis of chloride distribution (Cl-cell/Cl-medium) in equilibrated cells ranged from -13 to -32 mV. 7. Addition of glucose to cells equilibrated at 37 degrees C for 30 min in the presence of rotenone led to a decrease in fluorescent intensity indicating hyperpolarization. Addition of ouabain in turn led to a 70 to 100% reversal of fluorescent intensity. This hyperpolarization is therefore probably due to the electrogenic activity of the sodium pump. 8. The addition of amino acids known to require external Na+ for transport increased fluorescent intensity (depolarization) reaching a maximum at higher concentrations of amino acids. Plots of 1/deltafluorescence vs. 1/[glycine] were linear with an apparent Km of 2-3 mM. The increase in fluorescence with amino acids always required external Na+. Plots of 1/fluorescence vs. 1/[Na+]medium were also linear with an apparent Km of 29 mM. These apparent Km values compare favorably with those derived from amino acid transport studies using tracers. These data indicate that the Na+-dependent transport of amino acids in these cells is electrogenic.

The transport of chloride in Ehrlich ascites tumor cells

The steady state transport and distribution of chloride between the intracellular and extracellular phases was investigated when the extracellular chloride concentration was varied by isosmotic replacement with nitrate, bromide and acetate. The results of these experiments show that chloride transport, measured by uptake of 36Cl, is sensitive to the replacement anion. In the presence of nitrate, chloride transport is a linear function of the extracellular chloride concentration. The relationship between chloride transport and extracellular chloride in the presence of bromide is concave upward which suggests that this anion inhibits chloride movement. However, when acetate replaces chloride, the relationship between chloride transport and extracellular chloride is concave downward. The chloride distribution ratio of cells incubated in 145-155mM chloride medium is 0.386 and is not effected by the replacement of chloride with nitrate, bromide or acetate. These findings are consistent with the assertion that chloride transport is composed of two parallel pathways, a diffusional plus a saturating, mediated component. Of the total chloride flux (9.1 mmoles Cl-/kg dry weight per minute) measured in chloride medium (145-155 mM Cl-), the mediated component represents 40% and the diffusional component 60%.

Concanavalin A-induced alterations in sodium and potassium content of Ehrlich ascites tumor cells

Net fluxes of sodium and potassium were studied in Ehrlich mouse ascites tumor cells during contact with the agglutinating protein, concanavalin A. This lectin altered cation transport markedly at concentrations of 20–105 μg/ml (6–47 μg/mg cell protein). Whereas control cells extruded sodium and maintained or accumulated potassium against electrochemical gradients, in the presence of concanavalin A there was rapid net sodium entry and potassium loss. After 10–20 minutes in concanavalin A, sodium extrusion began and potassium loss diminished but these events were prevented by ouabain. The alterations in cation content induced by concanavalin A are unlikely to be the result only of agglutination since soybean agglutinin caused much smaller changes although it agglutinated the cells equally well.

The effect of external anions on steady-state chloride exchange across ascites tumour cells

1. The rate of cell chloride exchange, or efflux coefficient, was measured after equilibration in media of different anionic composition.2. When sulphate substituted for chloride in the medium, the efflux coefficient was always higher than in control chloride solutions and varied inversely with external chloride concentration. In sulphate the chloride efflux coefficient varied from 19.6 to 100.7 hr(-1). The mean control efflux coefficient was 6.60 +/- 0.677 (S.E. of mean).3. In contrast, when external nitrate substituted for chloride, the efflux coefficient was independent of external chloride concentration and the same as in control chloride media. The mean value in nitrate was 6.42 +/- 0.603 (S.E. of mean). The results confirm findings of Hempling & Kromphardt (1965).4. Steady-state chloride flux varied in direct proportion to the external chloride concentration, which would be expected for passive chloride exchange. However, the slope of the line relating these variables was higher in sulphate than in nitrate and control media. Thus at any given external chloride concentration chloride flux was greater in sulphate than in nitrate and control solutions.5. It is suggested that the effect of sulphate to increase cell chloride exchange may be related to its greater tendency to bind water, relative to chloride and nitrate.

The effect of calcium ions on the glycolytic activity of Ehrlich ascites-tumour cells

1. Added Ca(2+) inhibited lactate formation from sugar phosphates by intact Ehrlich ascites-tumour cells. Lactate formation from glucose by these cells was unaffected by added Ca(2+). 2. The Ca(2+) inhibition of lactate formation by intact cells occurred in the extracellular medium. 3. Intact ascites-tumour cells did not take up Ca(2+)in vitro. 4. Glycolysis of sugar phosphates by cell extracts as well as pyruvate formation from 3-phosphoglycerate and phosphoenolpyruvate was inhibited by Ca(2+). 5. It was concluded that Ca(2+) inhibited the pyruvate-kinase (EC 2.7.1.40) reaction. Further, Ca(2+) inhibition of pyruvate kinase could be correlated with the overall inhibition of glycolysis. 6. Concentrations of Ca(2+) usually present in Krebs-Ringer buffers, inhibited glycolysis and pyruvate-kinase activity by approx. 50%. 7. The inhibition of glycolysis by added Ca(2+) could be partially reversed by K(+) and completely reversed by Mg(2+) or by stoicheiometric amounts of EDTA. 8. The hypothesis is advanced that the inability of tumour cells to take up Ca(2+) is a factor contributing towards their high rate of glycolysis.