Lymphocyte monovalent cation metabolism: cell volume, cation content and cation transport

Glucocorticoid-induced plasma membrane depolarization during thymocyte apoptosis: association with cell shrinkage and degradation of the Na(+)/K(+)-adenosine triphosphatase

Multiple signaling pathways are known to induce apoptosis in thymocytes through mechanisms that include the loss of mitochondrial membrane potential, cell shrinkage, caspase activation, and DNA degradation but little is known about the consequences of apoptosis on the properties of the plasma membrane. We have previously shown that apoptotic signals, including survival factor withdrawal and glucocorticoids, induce plasma membrane depolarization during rat thymocyte apoptosis, but the mechanisms involved in this process are unknown. We report here that inhibition of the Na(+)/K(+)-adenosine triphosphatase (Na(+)/K(+)-ATPase) with ouabain similarly depolarized control thymocytes and enhanced glucocorticoid-induced membrane depolarization, suggesting a link between Na(+)/K(+)-ATPase and plasma membrane depolarization of thymocytes. To determine whether repression of Na(+)/K(+)-ATPase levels within cells can account for the loss of plasma membrane potential, we assessed protein levels of the Na(+)/K(+)-ATPase in apoptotic thymocytes. Spontaneously dying thymocytes had decreased levels of both catalytic and regulatory subunits of Na(+)/K(+)-ATPase, and glucocorticoid treatment enhanced the loss of Na(+)/K(+)-ATPase protein. The pan caspase inhibitor (z-VAD) blocked both cellular depolarization and repression of Na(+)/K(+)-ATPase in both spontaneously dying and glucocorticoid-treated thymocytes; however, specific inhibitors of caspase 8, 9, and caspase 3 did not. Interestingly, glucocorticoid treatment simultaneously induced cell shrinkage and depolarization. Furthermore, depolarization and the loss of Na(+)/K(+)-ATPase protein were limited to the shrunken population of cells. The data indicate an important role for Na(+)/K(+)-ATPase in both spontaneous and glucocorticoid-induced apoptosis of rat thymocytes.

Ca(2+)-activated K+ channels in rat thymic lymphocytes: activation by concanavalin A

1. The role of ion channels in the mitogenic response of rat thymic lymphocytes to concanavalin A (ConA) was studied using single-channel patch-clamp recordings and measurements of membrane potential with the fluorescent probe bis-oxonol. 2. ConA (20 micrograms ml-1) evoked a rapid membrane hyperpolarization; Indo-1 measurements indicated a concurrent increase in [Ca2+]i. The hyperpolarization was blocked by cytoplasmic loading with the Ca2+ buffer BAPTA (bis(O-amino-phenoxy)ethane-N,N,N',N'-tetraacetic acid), or charybdotoxin, a component of scorpion venom known to block K+ channels in lymphocytes. 3. Cell-attached patch-clamp recordings showed that both ConA and the Ca2+ ionophore ionomycin activated channels with high selectivity for K+. Two conductance levels were observed -6-7 pS and 17-18 pS-measured as inward chord conductance at 60 mV from reversal potential (Erev) with 140 mM-KCl in the pipette. The current-voltage relationship for the larger channel displayed inward rectification and channel open probability was weakly dependent upon membrane potential. 4. These experiments provide the first direct evidence for mitogen-activated Ca(2+)-gated K+ channels (IK(Ca)) in lymphocytes. This conductance is relatively inactive in unstimulated rat thymocytes but following the intracellular Ca2+ rises induced by ConA, IK(Ca) channels are activated and produce a significant hyperpolarization of the cell potential.

Ca2(+)-activated K+ channels in human B lymphocytes and rat thymocytes

1. Previous evidence for the existence of Ca2(+)-activated K+ channels in lymphocytes comes from measurements using voltage-sensitive dyes and from tracer flux studies. We have now directly measured these channels in human tonsillar B lymphocytes and rat thymocytes in single-channel recordings from cell-attached and excised patches. 2. In cell-attached recordings, intracellular Ca2+ was raised by either ionomycin or replacement of external Ca2+ following incubation in Ca2(+)-free medium. Indo-1 measurements during the Ca2(+)-replacement technique showed that [Ca2+]i rose from approximately 90 to 260 nM. Both techniques activated two channels of approximately 25 and 8 pS (slope conductance at 0 mV applied, with 140 mM-K+ in the pipette). Over 90% of patches displayed this activity, indicating a high density of these channels in the membrane. 3. Both channels reversed near the K+ equilibrium potential with either KCl or potassium aspartate in the pipette, when the cells were bathed in normal or high-K+ saline. Therefore, these channels are selective for K+. 4. The larger channel was studied in more detail. It displayed inward rectification in symmetrical K+ solutions. The open-channel probability was weakly dependent on membrane potential. 5. Ca2(+)-dependent K+ channels were also recorded from excised, inside-out membrane patches. The threshold for activation was 200-300 nM [Ca2+i]. 6. Patch excision altered some characteristics of IK(Ca). Channels were activated in fewer than 50% of patches and the main conductance level was approximately 34 pS (at -80 mV). The duration of single-channel events was shorter than in cell-attached patches; kinetic analysis suggested that this was due to the loss of an open state in excised patches. 7. We conclude that B and T lymphocytes have K(+)-selective channels which are activated by internal [Ca2+] in the physiological range and which will influence the membrane potential during cell activation.

Regulation of Na+ and K+ contents in rat thymocytes

A modified nystatin technique allowed the investigation of the initial rate of Na+ efflux as a function of internal Na+ content under steady-state conditions in rat thymocytes. This kinetic study showed that 1) ouabain-sensitive Na+ efflux as a function of internal Na+ can be adjusted by a three-sites kinetic model, with a maximal pump rate of 581 +/- 79 mmol.l cells-1.h-1 and an apparent dissociation constant for internal Na+ of 10.0 +/- 1.0 mmol/l cells (mean +/- SE of 3 experiments), 2) bumetanide-sensitive Na+ efflux was extremely low compared with the pump efflux (approximately 1%), and 3) ouabain- and bumetanide-resistant Na+ efflux was almost a linear function of internal Na+ content (as expected for a Na+ leak). This "all-pump" mechanism of thymocyte Na+ regulation was confirmed by non-steady-state experiments showing that 1) ouabain induced a rapid net Na+ gain and K+ depletion in fresh thymocytes and completely blocked the recovery of normal cation contents in Na+-loaded-K+-depleted thymocytes, and 2) bumetanide was unable to modify thymocyte Na+ and K+ contents. Na+ extrusion by Na+-loaded thymocytes was unaffected by prostaglandin E2, isoproterenol, or platelet-aggregating factor (PAF) and was slightly impaired in the adult spontaneously hypertensive rat of the Okamoto strain (10% lower rate constant for net Na+ extrusion, P less than 0.05). Concerning cell Na+ regulation, our results do not support the concept that rat thymocytes are more representative of vascular cells than enucleated erythrocytes.

Trans-stimulation of L-system amino acid transport in normal and chronic leukemic human lymphocytes: phorbol ester restores function in CLL

Chronic lymphocytic leukemia (CLL) B-lymphocytes have a unique and specific diminution of L-system (leucine favoring) amino acid uptake; the maximal velocity is approximately 10% of normal B-lymphocytes. Treatment of CLL B-cells with the maturational agent, tetradecanoyl phorbol acetate, results in restoration of L-system amino acid uptake to normal velocity. To further characterize the effect of phorbol ester on the L-system of CLL B-cells, we have examined the ability of normal and CLL lymphocytes to exchange intracellular for extracellular amino acids by the L-system (trans-stimulation). A 60% increase in L-system uptake was noted in normal B- and T-lymphocytes in the presence of a high intracellular concentration of 2-amino-2-carboxy-bicycloheptane (BCH), a largely L-system-specific substrate. L-system transport was not trans-stimulated in CLL B-lymphocytes. Phorbol ester treatment restored L-system uptake in CLL to a normal Vmax of 900 mumol/liter cell water per minute in the absence of BCH loading. The Vmax could be increased further to 2,400 if phorbol ester-treated CLL cells were loaded with BCH. Hence, phorbol esters result not only in a normalization of L-system uptake in CLL B-cells but the transport system demonstrates exchange rates comparable to normal lymphocytes.

Plasma membrane potential of Lettré cells does not depend on cation gradients but on pumps

The plasma membrane potential of Lettré cells has been determined with the optical indicator oxonol-V and found to be -57 mV at 37 degrees C (range -20 to -80 mV depending on the physiological condition of the cells). Increasing extracellular K+ does not depolarize cells: even in the presence of 155 mM K+ the potential is -41 mV; membrane potential is also insensitive to the chemical gradient of Na+, Mg2+, Ca2+ or Cl-. Ouabain depolarizes the cells; H+ efflux from cells is stimulated by extracellular Na+. We propose that in Lettré cells the plasma membrane potential is generated by electrogenic cation pumps. The balancing fluxes of Na+ and K+ are mainly through electroneutral cation exchanges (Na+/K+ and Na+/H+) and the magnitude of the potential is limited by organic anion leaks. Such a mechanism may operate in other biological membranes also.

Self-exchange of sodium in human lymphocytes

Self-exchanges of Na and K in human lymphocytes were measured by isotopic efflux techniques. In washed cells, K exchanged in a single slow exponential fraction, but the Na exchange had a marked curvature. It was shown that the curvature was not caused by simple bulk-phase diffusion, and it was resolved into three major fractions: fast (F) (half-time, t1/2 = 2-4 min), intermediate (I) (t1/2 = 12 min), and slow (S) (t1/2 = 125 min). Each of these appeared to follow an exponential function. The I fraction contained approximately 10 mmol Na/kg cells (25-30% of normal cellular Na), was not affected by manipulations that cause lymphocytes to gain Na, and had little or no temperature dependence. The S fraction of Na in normal cells (S1) contained approximately 10 mmol Na/kg cells, had only a slight temperature dependence, and the amount and rate of S1 were independent of external K concentration (Kex). Another slow fraction (S2) appeared when the cells underwent a net gain of Na in exchange for K, and was characterized by a steep temperature dependence and a peak rate around the transition point (the point at which half of cellular K is replaced by Na) at 0.4 mM Kex. The results are discussed within context of a theory that assigns the exchange of the major part of K in its slow exponential fraction and the Na exchange in S2 to interactions of these ions with fixed anionic sites, on intracellular macromolecules, which have been shown previously to interact cooperatively in their association with K and Na.

The permeability of human lymphocytes to chloride

The normal amount of Cl in human lymphocytes is 82 mmoles/kg wet weight. Half of this undergoes rapid self-exchange with a half-time of 3 minutes, while the remainder exchanges slowly with a half-time of 180 minutes. The fast fraction of self-exchange of Cl also undergoes a rapid net loss into medium with a low concentration of Cl. Thus, exchange of Cl in lymphocytes has properties like that of K and Na with permeability constants on the order of 10(-6) cm/sec. The results are compatible with a simple model in which the fast fractions are dissolved within ordered cellular water at concentrations less than in the external medium and the slow fractions are adsorbed onto intracellular macromolecules.

Responses of lymphocytes to anisotonic media: volume-regulating behavior

The regulatory responses elicited in lymphoid cells suspended in anisotonic media are reviewed. The immediate response approximates osmometric behavior. In addition, in hypotonic media, the initial osmometric swelling is followed by a regulatory volume decrease (RVD), which is associated with KCl loss. The volume-induced effluxes of K+ and Cl- are mediated by two independent conductive pathways. Ca2+-depletion experiments and studies of inhibitor susceptibility suggest that Ca2+ may mediate the activation of the K+ pathway. The responses of the two main lymphocyte subpopulations to hypotonic challenge are different. RVD is much more rapid in T- than in B-cells, regardless of their tissue of origin. Under certain conditions, shrunken lymphocytes will regain their initial volume. This regulatory volume increase (RVI) is due to NaCl uptake, followed by a secondary exchange of Na+ for K+ via the Na+-K+ pump. Na+ is primarily taken up in exchange for H+ through an amiloride-sensitive pathway, whereas Cl- enters in exchange for HCO-3 (or OH-). Anion and cation fluxes responsible for RVI are electroneutral. Some of the volume-sensitive pathways can also be activated in isotonic cells. The conductive K+ pathway is activated by Ca2+ plus ionophore A23187, and the Na+-H+ exchanger can be activated by cytoplasmic acidification. The responses of lymphocytes to anisotonic challenge are compared with those of other cells, and the possible significance of the volume-induced fluxes is discussed.

Cytoplasmic pH regulation in thymic lymphocytes by an amiloride-sensitive Na+/H+ antiport

The mechanisms underlying cytoplasmic pH (pHi) regulation in rat thymic lymphocytes were studied using trapped fluorescein derivatives as pHi indicators. Cells that were acid-loaded with nigericin in choline+ media recovered normal pHi upon addition of extracellular Na+ (Nao+). The cytoplasmic alkalinization was accompanied by medium acidification and an increase in cellular Na+ content and was probably mediated by a Nao+/Hi+ antiport. At normal [Na+]i, Nao+/Hi+ exchange was undetectable at pHi greater than or equal to 6.9 but was markedly stimulated by internal acidification. Absolute rates of H+ efflux could be calculated from the Nao+-induced delta pHi using a buffering capacity of 25 mmol X liter-1 X pH-1, measured by titration of intact cells with NH4+. At pHi = 6.3, pHo = 7.2, and [Na+]o = 140 mM, H+ extrusion reached 10 mmol X liter-1 X min-1. Nao+/Hi+ exchange was stimulated by internal Na+ depletion and inhibited by lowering pHo and by addition of amiloride (apparent Ki = 2.5 microM). Inhibition by amiloride was competitive with respect to Nao+. Hi+ could also exchange for Lio+, but not for K+, Rb+, Cs+, or choline+. Nao+/Hi+ countertransport has an apparent 1:1 stoichiometry and is electrically silent. However, a small secondary hyperpolarization follows recovery from acid-loading in Na+ media. This hyperpolarization is amiloride- and ouabain-sensitive and probably reflects activation of the electrogenic Na+-K+ pump. At normal Nai+ values, the Nao+/Hi+ antiport of thymocytes is ideally suited for the regulation of pHi. The system can also restore [Na+]i in Na+-depleted cells. In this instance the exchanger, in combination with the considerable cytoplasmic buffering power, will operate as a [Na+]i-regulatory mechanism.

The bivalent-cation dependence of phosphatidylinositol synthesis in a cell-free system from lymphocytes

The bivalent-cation requirements of two enzymes involved in phosphatidylinositol synthesis were defined for pig lymphocyte membranes using a citric acid buffer. CTP:phosphatidic acid cytidylyltransferase (EC 2.7.7.41) is activated by free Mn2+ concentrations above 20nM and by free Mg2+ concentrations above 10 microM. When activated by Mg2+, the enzyme is weakly inhibited by Ca2+ (Ki greater than 250 microM), but Ca2+ has no effect when Mn2+ is used to stimulate CDP-diacylglycerol synthesis. The synthesis of phosphatidylinositol from phosphatidic acid is also stimulated by Mn2+ and Mg2+ concentrations similar to those above and is inhibited by free Ca2+ concentrations above 500nM, probably by its action on CDP-diacylglycerol:inositol 3-phosphatidyltransferase (EC 2.7.8.11). Taken together, these studies suggest that under physiological conditions phosphatidylinositol synthesis is activated by Mg2+ and it is possible that it is further regulated by the free concentrations of Ca2+ and/or Mn2+.

Concanavalin A causes an increase in sodium permeability and intracellular sodium content of pig lymphocytes

1. The 3mV depolarization of pig lymphocytes observed within 2 1/2 min of treatment with concanavalin A [Felber & Brand (1983) Biochem. J. 210, 885-891] is dependent on the presence of high extracellular [Na+]. 2. The concanavalin A-induced changes in membrane potential at high and low extracellular [Na+] are quantitatively explained by an increase in the electrogenic permeability coefficient for Na+ (PNa). This rises from a negligible value in resting cells to around 4% of the permeability coefficient for K+ or Cl- in stimulated cells. 3. Concanavalin A induces a 4mM increase in the Na+ content of pig lymphocytes. This increase in intracellular [Na+] is not due solely to stimulation of electrogenic Na+ influx resulting from the rise in PNa. 4. Thus concanavalin A stimulates both an electrogenic pathway for Na+ influx, resulting in a small depolarization of the plasma membrane, and a non-electrogenic Na+ influx pathway, resulting in a rise in intracellular [Na+].

Fc gamma of IgG: a specific agent of destabilization of lipid bilayers containing oleic acid

gamma-Immunoglobulins induce the fusion of oleic acid-containing liposomes into tubular structures. An F(ab')2 preparation does not exert the same influence unless it is several orders of magnitude more concentrated. The same is true for several proteins with an isoelectric point higher or lower than the IgG isoelectric point. The Fc of IgG seems thus to exert a specific destabilizing and fusogenic action on artificial lipid membranes. An hypothesis is presented concerning the mode of action of Fc gamma on lymphocyte membrane which is based on the facts mentioned above and on the existence of a phospholipasic activity of Fc gamma membrane receptor.

Factors determining the plasma-membrane potential of lymphocytes

1. Lymphocytes from pig mesenteric lymph node have low permeability to K+ (Rb+), Na+ and Cl-. None of these ions is in Nernst equilibrium with the plasma-membrane potential (delta psi p). 2. delta psi p can be calculated from the transmembrane distribution of the permeant cation methyltriphenylphosphonium (TPMP+) in the presence of the uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) to abolish uptake into intracellular mitochondria. In normal culture medium delta psi p is 56 mV. 3. A similar potential is found in T-enriched pig cells and in mouse thymocytes. 4. The contribution of electrogenic (Na+ + K+)ATPase to delta psi p is about 7 mV. 5. The remainder of the lymphocyte delta psi p is a polyionic potential set up by K+ and Cl- with a permeability coefficient for Cl- of similar magnitude to that for K+.

Distinction between normal and leukemic bone marrow by water protons nuclear magnetic resonance relaxation times

Pulsed nuclear magnetic resonance studies have been carried out on bone marrow of normal human subjects and patients with leukemia: chronic myeloid leukemia (CML) and acute myeloid leukemia (AML). It was observed that the proton spin-lattice relaxation time (T1) value was discriminatory in the normal and leukemic cases with a statistical significance of (p less than 0.01). Ouabain treatment of cells did not show any perceptible change of T1 value when compared with the nontreated cells, indicating that the concomitant cation effluxes do not affect spin-lattice relaxation time. The water contents of normal, leukemic, and ouabain treated cells were in the range 60%-80%. Higher Fe levels were encountered in the normal than the leukemic samples, while levels of Zn, Cu, Mn, Co, and Ni were elevated in the leukemic samples compared with the normals. Despite the T1 differences observed, the multiparameter studies do not uniquely pinpoint factors responsible for the elevation of T1 in the malignant state.

Cap formation by various ligands on lymphocytes shows the same dependence on high cellular ATP levels

The effects of inhibitors of mitochondrial ATP synthesis and the calcium ionophore, A23187, on the capping of surface immunoglobulin, concanavalin A receptors and theta antigen on mouse spleen or thymus cells have been examined. (i) For all of these capping ligands and inhibitors, the cellular ATP level must be above 80% of the normal level in resting lymphocytes for 90% of maximal cap formation to occur. Below 50% of the normal ATP level, less than 10% of maximal capping occurs. There is, therefore, a common dependence for all three capping systems on the cellular ATP level, irrespective of the metabolic inhibitor used. (ii) Inhibition of cap formation by A23187 follows the same profile for ATP dependence as the mitochondrial inhibitors, but in contrast to those inhibitors, A23187 requires extracellular calcium to decrease the ATP level and inhibit capping. Other agents can affect cap formation without reducing the ATP level. For example, concanavalin A inhibits its own cap formation and cytochalasin B reduces the rate of cap formation at concentrations which do not alter the cellular ATP level. (iii) From these and other data we conclude that there are cellular functions essential for cap formation, other than the maintenance of ionic gradients, that require a high concentration of cellular ATP. The possibility that high levels of ATP are required for the function of the cytoskeleton in lymphocytes is discussed.

Membrane potential changes during mitogenic stimulation of mouse spleen lymphocytes

By monitoring differences in accumulation of the lipophilic cation [(3)H]tetraphenylphosphonium in media containing low or high potassium concentrations [Lichtshtein, D., Kaback, H. R. & Blume, A. J. (1979) Proc. Natl. Acad. Sci. USA 76, 650-654], the membrane potential of lymphocytes from various sources has been estimated. On the basis of this method, the potential of normal mouse spleen lymphocytes (T and B cells) is -65 +/- 2 mV (mean +/- SEM, interior negative). During the course of mitogenic stimulation by concanavalin A, lipopolysaccharide, or fetal calf serum, the membrane potential of murine spleen lymphocytes changes systematically according to the following pattern: (i) early depolarization lasting 2-3 hr, (ii) repolarization over the next 7 hr, and (iii) a final hyperpolarization phase during the last 24-48 hr. During repolarization and hyperpolarization, moreover, there is a direct correlation between the membrane potential and DNA synthesis, as judged by [(3)H]thymidine incorporation. By using isolated T and B cells, it is observed that concanavalin A depolarizes T cells only, whereas lipopolysaccharide depolarizes B cells only. Thus, both mitogens exhibit the same specificity for depolarization as for mitogenic stimulation. On the basis of these observations, it is suggested that the transition of lymphocytes from a resting state to mitotic activity is initiated by depolarization of the plasma membrane.

Lymphocyte membrane potential assessed with fluorescent probes

The membrane potential of mouse spleen lymphocytes has been assessed with two fluorescent probes. 3,3'-Dipropylthiadicarbocyanine (diS-C3-(5)) was used for most of the experiments. Solutions with high K+ concentrations depolarised the cells. Valinomycin, an inophore which adds a highly K+-selective permeability membranes, slightly hyperpolarised cells in standard (6 mM K+) solution, and in 145 mM K+ solution produced a slight additional depolarisation. These findings indicate a membrane whose permeability is relatively selective for K+. Very small changes in potential were seen when choline replaced Na+, or gluconate replaced Cl-, supporting the idea of K+ selectivity. The resting potential could be estimated from the K+ concentration gradient at which valinomycin did not change the potential-the "valinomycin null point" - and under the conditions used the resting potential was approx.-60 mV. B cell-enriched suspensions were prepared either from the spleens of nu/nu mice or by selective destruction of T cells in mixed cell populations. The membrane potential of these cells was similar to that estimated for the mixed cells. In solution with no added K+, diS-C3-(5) itself appeared to depolarise the lymphocytes, in a concentration dependent manner. With the 100 nM dye normally used, the membrane potential in K+-free solution was around -45 mV, and 500 nM dye almost completely depolarised the cells. In standard solution quinine depolarised the cells. Valinomycin could still depolarise these cells indicating that depolarisation had not been due to dissipation of the K+ gradient. Since in K+-free solution diS-C3-(5) blocks the Ca2+-activated K+ channels in human red blood cell ghosts and quinine also blocks this K+ channel it is suggested that the resting lymphocyte membrane may have a similar Ca2+-activated K+ permeability channel. Because of the above mentioned effect of diS-C3-(5) and other biological side effects, such as inhibition of B cell capping, a chemically distinct fluorescent probe of membrane potential, bis(1,3-diethylthiobarbiturate)-trimethineoxonol was used to support the diS-C3-(5) data. This new probe proved satisfactory except that it formed complexes with valinomycin, ruling out the use of this ionophore. Results with the oxonol on both mixed lymphocytes and B cell-enriched suspensions gave confirmation of the conclusions from diS-C3-(5) experiments and indicated that despite its biological side effects, diS-C3-(5) could still give valid assessment of membrane potential.

Transmembrane electrical and pH gradients across human erythrocytes and human peripheral lymphocytes

Transmembrane electrical and pH gradients have been measured across human erythrocytes and peripheral blood lymphocytes using equilibrium distributions of radioactively labelled lipophilic ions, and of weak acids and weak bases, respectively. The distributions of methylamine, trimethylamine, acetic acid and trimethylacetic acid give calculated transmembrane pH gradients (pHe-pHi) for erythrocytes of between 0.14-0.21 for extracellular pH values of 7.28-7.16. The distributions of trimethylacetic acid. DMO and trimethylamine were determined for lymphocytes, establishing upper and lower limits of the calculated pH gradient over the external pH range of 6.7 to 7.7. Tritiated triphenylmethyl phosphonium ion (TPMP) and 14C-thiocyanate ion (SCN) equilibrium distributions were measured in order to calculate transmembrane electrical potentials, using tetraphenylboron as a catalyst to facilitate TPMP equilibrium. Transmembrane potentials of -7 to -10 mV were calculated from SCN and TPMP, respectively for red cells, and -35 to -52 mV respectively, in the case of lymphocytes. Distributions of TPMP and potassium ions were determined in the presence of valinomycin over a wide range of extracellular potassium concentrations for red cells and the calculated Nernst potentials for TPMP compared to the calculated potential using the Goldman equation for chloride and potassium ions. Distributions of TPMP, SCN and potassium ions were also determined for lymphocyte suspensions as a function of extracellular potassium and the calculated Nernst potentials for TPMP and SCN compared to the calculated potassium diffusion potential.

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+.

Studies of (Na+ + K+)-sensitive ATPase activity in pig lymphocytes. Effects of concanavalin A

(Na+ + K+)-ATPase activity is demonstrated in plasma membranes from pig mesenteric lymph nodes. After dodecyl sulfate treatment plasma membranes have an 18-fold higher (Na+ + K+)-ATPase activity, while their ouabain-insensitive Mg2+-ATPase is markedly lowered. A solubilized (Na+ +K+)-ATPase fraction, obtained by Lubrol WX treatment of the membranes, has very high specific activity (21 mumol Pi/h per mg protein). Concanavalin A has no effect on these partially purified (Na+ + K+)-ATPase, while inhibits (40%) this activity in less purified fractions which still contain Mg2+-ATPase activity.

Osmotic properties of human lymphocyte

The osmotic properties of human lymphocytes isolated from 15 ml of venous blood were examined. Measurements of the permeability of the membrane to water under an osmotic gradient were also made. The Boyle-Van't Hoff relation held very well for the human lymphocyte when the cells were shrunken in hyperosmotic media to concentrations twice isosmotic. The volume of osmotically inactive material or "b" value averaged 32% of the mean corpuscular volume. These values were independent of temperature. Ponder's R ranged between 0.8 and 0.9. The average value for Lp, the hydralic coefficient was 0.46 mu/min atm +/- 0.02 (S.E.M.) at 25 degrees C. No significant effect of age, sex, or race was noted. The effect of temperature between 10 degrees C and 37 degrees C was measured and heats of activation between 11.1 and 17.4 kcal/mole were calculated with a mean of 14.1 kcal/mole +/- 1.6 (S.E.M.). Concanavalin A at 10 microgram/1.5 X 10(6) lymphocytes produced blastogenesis of 25% or more of the lymphocytes without clumping, agglutination, or toxicity. The mean corpuscular volume increased by 21% after 72 hours due to an increase in the "b" value which increased by 80%. The volume of free water remained constant. Histograms of the distribution of cell volumes showed that volume changes were uniform throughout the population with no evidence of agglutination of clumping. The significance of these results is discussed in the context of membrane fluidity and the state of intracellular water.

Decreased membrane potassium permeability and transport in human chronic leukemic and tonsillar lymphocytes

Human blood T-lymphocytes increase their potassium (K+) permeability and active K+ transport following lectin or antigen stimulation. We have studied the permeability and active transport of K+ by lymphocytes in chronic lymphocytic leukemia (CLL) to determine if their membrane K+ transport was similar to resting or lectin-stimulated normal blood lymphocytes. K+ transport was assessed both by the rate of isotopic 42K+ uptake and by the rate of change in cell K+ concentration after inhibition of the K+ transport system with ouabain. CLL lymphocytes had a marked decrease in membrane K+ permeability and active transport of K+ when compared to blood T lymphocytes. K+ transport in five subjects with CLL (10 mmol.1 cell water-1.h-1) was half that in normal blood T-lymphocytes (20 mmol.1 cell water-1 h-1). Phytohemagglutinin (PHA) treatment of CLL lymphocytes did not increase significantly their active K+ transport, whereas K+ transport by normal T-lymphocytes increased by 100%. Since there were 73% T-lymphocytes in normal blood and 14% in CLL blood, the difference in membrane K+ turnover could be related either to neoplasia or to the proposed B-lymphocyte origin of CLL. We studied human tonsillar lymphocytes which contained a mean of 34% T-cells. In five studies of tonsils, K+ transport was 14 mmol.1 cell water-1.h-1 and treatment with PHA increased K+ transport only 30%. The intermediate values of basal K+ transport and K+ transport in response to PHA in tonsillar lymphocytes were consistent with the proportion of T-lymphocytes present. These data suggest that B-lymphocytes have reduced membrane permeability and active transport of K+. Thus the marked decrease in CLL lymphocyte membrane K+ permeability and transport may be a reflection of its presumed B-cell origin, rather than a membrane alteration related to malignant transformation.

Potasssium transport in human blood lymphocytes treated with phytohemagglutinin

We have confirmed that phytohemagglutinin (PHA) rapidly enhances the uptake of potassium (K+) by human blood lymphocytes. PHA, however, did not produce an increase in lymphocyte K+ concentration. The apparent steady-state of cell K+ concentration despite the marked increase in uptake of 42K+ could be explained by either an increase in K+-K+ exchange or an increase in concentrative (active) K+ accumulation in association with an increase in the leak of K+ from the cell. We compared, therefore, the uptake of 42K+ with the decrement in cellular K+ content when active transport was inhibited by ouabain. These studies established that K+-K+ exchange was negligible in human blood lymphocytes and that the increase in 42K+ uptake after PHA treatment represented concentrative transport. Our studies did indicate that 42K+ exodus from PHA treated lymphocytes increased markedly from 19 to 38 mmol-1 cell water-1-h-1. Within the same time period K+ influx into PHA-treated lymphocytes increased from 20 to 38 mmol-1 cell water-1-h-1. Thus, PHA produces a marked increase in the permeability of the lymphocyte membrane to K+, and the increase in active K+ influx in PHA-treated lymphocytes may represent a homeostatic response by the membrane K+ transport system to the increase in K+ efflux. Increased K+ turnover was observed at the lowest concentrations of PHA which produced an observable increase in [3H]thymidine incorporation into DNA. Thus, PHA produces an increase in K+ permeability that closely parallels its mitogenic effect. The rapid increase in K+ influx preceding blastogenesis and mitogenesis is required, therefore, to maintain normal intracellular K+ concentration. An adequate intracellular K+ concentration is essential for the synthetic processes required for cell transformation or division.

Unidirectional K+ fluxes in rat thymocytes stimulated by concanavalin A

Unidirectional K+ fluxes were estimated in isolated rat thymocytes by 42K exchange kinetics. The cells were either preloaded with isotope and the release of it measured during incubation for one hour at 38 degrees C, or the cellular uptake of isotope during a similar incubation was measured. The influx rate of untreated thymocytes was: 2.3-10(-12) moles cm-2-s-1 and efflux rate: 1.8-10(-12) moles cm-2-s-1. When con A was added to the cells, influx was raised 74% and efflux 65%. Maximal effect was obtained when the concentration of con A was 15 mug/ml, but concentrations as low as 0.75 mug/ml were effective. Hydrocortisone resistant thymocytes responded at least was well as untreated cells to con A, which also raised RNA synthesis rate in the former cells 2.5 times. Using an extracellular marker, 51CrEDTA, intracellular concentrations of some ions was estimated in the thymocytes after one hour incubation: Na+: 30 mmoles/kg water, K+: 177 mmoles/kg water and Cl-:43 mmoles/kg water. Cellular water content: 69%. These values were not found significantly altered when con A was present. Since con A raised influx and efflux to the same extent and no net flux of K+ could be detected, it is proposed that both active and passive transport of K+ was increased by con A. The increased fluxes induced by con A, can apparently not be reversed by removal of con A from the incubation medium or by addition of the inhibiting hapten, alpha-methyl-D-mannoside.

Exodus of 42K+ and 86Rb+ from rat thymic and human blood lymphocytes exposed to phytohemagglutinin

We have found that PHA produces an alteration in the lymphocyte membrane which allows 86Rb+ or 42K+ in prelabeled lymphocytes to exchange for cations present in washing solutions. These observations suggested that PHA might induce an increase in the exodus of intracellular potassium during incubation in physiologic media. We, therefore, examined 86Rb+ and 42K+ efflux from rat and human lymphocytes during incubation in tissue culture medium. The rate constant for efflux, Ke, was significantly increased by PHA. 86Rb+ efflux was increased by 27% in rat thymic lymphocytes and by 78% in human blood lymphocytes following PHA treatment.

A rapid phytohemagglutinin induced alteration in lymphocyte potassium permeability

The exposure of rat and human lymphoid cells to mitogenic concentrations of phytohemagglutinin resulted in an apparent decrease in cellular K+ without a significant change in cellular Na+ when the cells were washed with isotonic Hepes buffered choline chloride prior to cation determination. The apparent reduction in total cellular Na+ plus K+ concentration, however, was not accompanied by a change in cell volume. We inferred that the constant cell volume could occur only if the lost intracellular K+ was exchanged for an external cation during the washing procedure used to prepare cells for Na+ and K+ measurement. This inference was supported by the quantitative recovery of lost cellular K+ in the choline chloride washing solution and the demonstration that a comparable proportion of 86Rb+ (K+ analogue) 42K+ was lost from prelabelled cells during choline chloride washing. Use of medium 199 with Hanks salts, 150 mM NaCl, or 100 mM MgCl2 as the washing solution did not prevent K+ exchange although exchange was less in the presence of MgCl2. These findings indicate that phytohemagglutinin produces a rapid alteration in lymphocyte plasma membranes so as to allow abnormal K+ exchange. This observation is of importance because investigators who measure intracellular solutes in phytohemagglutinin-treated lymphocytes must consider the possibility of lossduring preparative washes. Also, changes in membrane permeability following phytohemagglutinin treatment may modulate mitogenesis and/or permit the transmission of chemical messages between cells.

The early effects of ouabain on potassium metabolism and rate of proliferation of mouse lymphoblasts

Murine lymphoblasts grown in suspension culture in the presence of ouabain showed a dose dependent and sequential decrease in 86Rb+ (K+ analogue) influx, cellular potassium content, and growth rate. An increase in eosin staining and a decrease in cell number was observed after two hours in the presence of 1 mM ouabain; 1 muM ouabain was without effect on any of the parameters measured. Ouabain inhibition was rapidly and completely reversible at concentrations that were not cytotoxic.

Adaptation of potassium metabolism and restoration of mitosis during prolonged treatment of mouse lymphoblasts with ouabain

The effects of ouabain on the growth of murine lymphoblasts in vitro have been studied. Exposure of cells to ouabain (0.1 mM) initially inhibited 86Rb+ uptake rate, reduced the intracellular potassium concentration, and decreased population growth rates. Continued exposure to the same ouabain concentration resulted in an increase of 86Rb+ uptake rate, intracellular potassium content and population growth rates to control values (adaptation). When treated cells were resuspended in medium free of ouabain after 12 to 15 hours of ouabain treatment, 86Rb+ uptake rates and intracellular potassium levels exceeded those of untreated cells. Adaptation was inhibited by cycloheximide (3 mug/ml) and by actinomycin D (0.05 mug/ml). Kinetic analysis of transport suggested that while the total capacity of the Na/, K+ transport system increased, the affinity for both the cation (86Rb+) and ouabain decreased.