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G B Segel

Publications and source records attributed to G B Segel.

At least 37 records · Page 2Linked to original sources
PubMed1986

Signal transduction in human monocytes: relationship between superoxide production and the level of kinase C in the membrane.

Activation of monocytes and neutrophils results in an increased production of superoxide, an important cytotoxic compound. The previous finding that two agents that induce superoxide production cause opposite translocation of kinase C (Costa-Casnellie et al. [1985] Biochem. Biophys. Res. Commun., 133:1139-1144). led us to study the role of kinase C in superoxide production. In monocytes induction of superoxide production by 13-tetradecanoate phorbol acetate requires translocation of kinase C from the cytosol to the membrane. Superoxide production is also induced by concanavalin A, but this induction is accompanied by a shift of kinase C from the membrane to the cytosol. Superoxide production by concanavalin A is greatly augmented by cytochalasin B. During activation by Con A and cytochalasin B the membrane kinase C is translocated to the cytosol in a manner similar to that observed in the presence of Con A alone. Under these conditions approximately 5-10% of kinase C remains associated with the membrane. Thus, induction of superoxide production by concanavalin A is independent of the levels of kinase C tightly bound to the membrane. We also show evidence that the concanavalin A-induced release of kinase C from the membrane is not due to an increase in levels of intracellular calcium or increased phosphoinositide turnover. In summary, these data indicate that concanavalin A and phorbol ester-induced superoxide production by human monocytes occurs by distinct pathways and that superoxide production is not closely correlated with specific levels of membrane-associated kinase C activity.

Cell Membrane↗
PubMed1986

Relationship of superoxide production to cytoplasmic free calcium in human monocytes.

Calcium has been proposed as an intracellular second messenger for activation of secretion, phagocytosis, and the oxidative burst of neutrophils. We have examined the role of calcium in human monocyte activation. Concanavalin A (Con A)-stimulated monocytes displayed an increment in cytoplasmic ionized calcium at 31 +/- 6 s and the onset of superoxide production at 61 +/- 9 s. The increase in cytoplasmic calcium invariably preceded the onset of superoxide production. If the external calcium concentration was reduced to less than 28 nM by the addition of 10 mM EGTA, superoxide production was not diminished at 5 min; however, superoxide production decreased thereafter. The Con A-evoked increment in cytoplasmic ionized calcium was blunted upon the addition of EGTA and decreased further with time. Both the production of superoxide and the Con A-evoked increment in cytoplasmic ionized calcium displayed a 50% inhibition after 15 min of calcium depletion and were completely inhibited after 60 min. Total cell calcium fell from 0.7 to 0.5 fmol/cell, and the basal level of ionized calcium fell from 83 to 30 nM after 60 min. Histidine, a strong chelator of divalent cations other than calcium and magnesium, had no effect on monocyte superoxide production or on ionized calcium concentrations, indicating that EGTA inhibition was due to cell calcium depletion. In calcium-depleted cells, Con A did not evoke superoxide production until calcium was restored to the incubation medium. The restoration of calcium to Con A-treated, calcium-depleted monocytes permitted a rapid rise in the cytoplasmic ionized calcium, and the production of superoxide within 9 s. These data suggest that an increase in ionized cytoplasmic calcium is necessary for the activation of monocyte superoxide production by Con A. The rise in ionized calcium in response to Con A results, in part, from an internal redistribution of calcium, which is sufficient to permit superoxide generation.

Aminoquinolines↗
PubMed1986

Variables influencing the timing of marrow transplantation in patients with chronic myelogenous leukemia.

The prognosis for patients with chronic myelogenous leukemia (CML) has improved only for patients who can receive marrow transplantation from a histocompatible sibling. The timing of the marrow transplant is made difficult by the high peritransplant mortality of 20% to 35% and a group of patients with a prolonged chronic phase of CML, which can be identified on the basis of prognostic indexes (age, percent blood myeloblasts, spleen size, and platelet count). We have developed a mathematic model and computer program that consider age, prognostic index, and projected survival rate by transplantation to balance the risk of peritransplant mortality against the risk of delaying the transplantation of patients with Philadelphia chromosome-positive CML. The computation assesses the risk of delaying transplantation; it does not offer the option of avoiding transplantation, since long-term survival ultimately requires transplantation. Three prognostic groups were considered as described by Sokal and co-workers (Blood 63:789, 1984) (I, best; II, intermediate; III, worst prognosis). The computation used the projected survival rates of transplantation from the Seattle experience and from the International Bone Marrow Transplant Registry. As an example of the model's utility, we have determined the ratio of the calculated life expectancy to the normal life expectancy for hypothetical patients up to 50 years of age in each of the three prognostic categories. A value of 20% is used for patients who successfully receive transplants after the onset of the accelerated phase. The analysis allows assessment of the risk of delaying transplantation for a finite time in patients with CML. The importance of the method rests in its consideration of multiple variables, including the peritransplant mortality, transplant projected survival before and upon entering the accelerated phase, age, prognostic group, and other risk factors. The program permits a change in these parameters as new information or advances in treatment occur. This analysis does not replace the diagnostic deliberations of the clinician. Rather, it provides a numeric framework for prognosis based on the currently available data. The physician in conjunction with the patient, not the algorithm, makes the decisions of whether and when to transplant.

Age Factors↗
PubMed1985

Concanavalin A and phorbol ester cause opposite subcellular redistribution of protein kinase C.

Concanavalin A and phorbol ester induce human blood monocytes to produce superoxide. We tested whether activation of human monocytes by these agents is accompanied by a subcellular redistribution of protein kinase C. Phorbol ester predictably caused a profound shift of the enzyme from the cytosol to the particulate fraction. In contrast concanavalin A induced a shift of the enzyme from the particulate fraction to the cytosol. The opposite effect of these agents on kinase C translocation was observed also by analysis of the phosphorylation of cytosolic proteins. Kinase C is either not involved in monocyte activation or does so by distinct pathways determined by the activating agent.

Coenzymes↗
PubMed1985

Y+- and L-system amino acid transport in normal and chronic lymphocytic leukemia lymphocytes: photoinhibition by fluoronitrophenylazide.

Three major pathways mediate amino acid transport into mammalian cells: the A-system and the ASC-system, which require a sodium gradient across the plasma membrane, and the L-system, which has no requirement for a sodium gradient. We have found that the lymphocytes from patients with B-cell chronic lymphocytic leukemia (CLL) have a marked reduction in the L-system of amino acid transport when compared to normal human B-lymphocytes from blood or tonsils. Transport by the A- and ASC-systems was not decreased in CLL B-lymphocytes. Because of the specific defect of the sodium-independent L-system amino acid transport in CLL cells, we have examined the activity of another sodium-independent transport system, the Y+-system, in human lymphocytes. The Y+-system favors the transport of dibasic, cationic amino acids such as lysine, ornithine, and arginine, which carry a positively charged group on their side chains. Our studies indicate that there is a large nonsaturable component of amino acid transport by the Y+-system in human lymphocytes. Using a multicomponent mathematical analysis, we have determined that the saturable component of Y+-transport is similar in T- (thymus-derived) and B- (bone-marrow-derived) lymphocytes and is unimpaired in CLL B-lymphocytes. Further, fluoronitrophenylazide, which was thought to be a specific inhibitor of the Y+-system when photoactivated, also inhibits A-, and L-system transport in CLL, T-, and B-lymphocytes.

Amino Acids↗
PubMed1985

The requirements for ionized calcium and magnesium in lymphocyte proliferation.

The extracellular ionized calcium and magnesium requirements for lectin-induced lymphocyte DNA synthesis were measured in a serum-free system. The use of this system permitted measurements of the ionized calcium and magnesium concentrations with ion-selective electrodes. Maximal DNA synthesis was observed at 270 microM ionized calcium and at 100 microM ionized magnesium in phytohemagglutinin-treated lymphocytes. Lymphocyte DNA synthesis was much more sensitive to reduction of external ionized calcium than to reduction of ionized magnesium. In calcium-free medium (ionized calcium 25 microM), DNA synthesis was reduced by 90%, but in magnesium-free medium (ionized magnesium concentration 7 microM) DNA synthesis was reduced by only 30%. Fifty percent of DNA synthesis stimulated by phytohemagglutinin (PHA) and concanavalin A (Con A) was observed at external ionized calcium concentrations of 97 and 43 microM, respectively. When lymphocytes were stimulated with PHA and the external calcium was chelated with EGTA, 50% inhibition of DNA synthesis was observed at 98 microM ionized calcium. This value agreed well with the free calcium required for PHA activation of DNA synthesis (97 microM). Cytoplasmic calcium, measured with the fluorescent probe Quin 2, increased following lectin exposure if the extracellular ionized calcium concentration was greater than 80 microM. No increase in cytoplasmic calcium could be detected in lectin-treated lymphocytes below 80 microM extracellular ionized calcium, although substantial DNA synthesis was sustained.

Calcium↗
PubMed1985

Ecto-nucleotide triphosphatase activity of human lymphocytes: studies of normal and CLL lymphocytes.

We have studied the apparent kinetic parameters of the ecto-nucleotide triphosphatase from CLL B lymphocytes and compared them to blood and tonsillar B and T cells. The Vmax of the ecto-ATPase activity in CLL B lymphocytes, was 65 +/- 10 fmol Pi/cell per 30 min compared to 37 +/- 2.1 in blood B lymphocytes, and 8.5 +/- 1.7 in blood T lymphocytes. The ATPase of membranes prepared from CLL, tonsillar B and T, and blood T lymphocytes had a relationship among the cell types similar to that seen in intact cells. However, no difference in the km for ATP, .17 mM, or the km for magnesium, .15 mM was found in the ecto-ATPase of CLL lymphocytes as compared to blood or tonsillar B cells. The ectoenzyme of CLL cells hydrolyzed GTP, ITP, CTP, and UTP as well as ATP. Further, ATP added to an enzyme assay containing an alternative nucleotide did not result in increased phosphate release. Nucleotide acceptance of blood B and T lymphocytes was very similar to that of CLL B cells. ATP inhibited phosphate release when present in excess of magnesium in both CLL and blood B lymphocytes. These data indicate that there is greater ectonucleotide triphosphatase activity in tonsillar and blood B lymphocytes, including CLL, as compared either to blood or tonsillar T lymphocytes. However, CLL cells showed no qualitative difference from blood or tonsillar B cells in ectonucleotidase activity. Thus, the higher activity in CLL cells is "B cell-like" and might reflect, also, their maturation stage or monoclonal origin.

Adenosine Triphosphatases↗
PubMed1984

Multicomponent analysis of amino acid transport in human lymphocytes. Diminished L-system transport in chronic leukemic B lymphocytes.

We have examined the amino acid transport in B cell chronic lymphocytic leukemia and compared it with the amino acid transport in isolated B lymphocytes from human blood and tonsils. L-system transport was measured with 2-amino-2-carboxy-bicyclo (2,2,1)-heptane, which is a synthetic amino acid whose transport is limited to the L-system. Amino acid uptake was subjected to a multicomponent analysis that partitioned the total uptake into the saturable carrier-mediated transport system and the uptake by diffusion. The maximal velocity of L-system transport in chronic lymphocytic leukemia cells, 81 mumol/1 cell water per min, was less than 10% that of blood B lymphocytes, which was 1,029 mumol/1 cell water per min. The uptake of 2-amino-2-carboxy-bicyclo (2,2,1)-heptane by tonsillar B cells, by a B lymphocyte cell line, and by blood T-lymphocytes was also 10-fold greater than that observed in chronic lymphocytic leukemic cells. Similarly, the L-system uptake of leucine and phenylalanine, which are naturally occurring amino acids usually transported primarily by the L-system, was reduced in chronic lymphocytic leukemic B cells to 15 and 10% of normal B cells, respectively. Total leucine uptake by chronic lymphocytic leukemic cells, however, was sustained at 30% of that expected because of transport via an alternative transport system. The A- or ASC-systems, the other major amino acid transport pathways, were not defective in chronic lymphocytic leukemic cells. These data indicate that there is a specific, profound decrease in L-system carrier-mediated amino acid transport in chronic lymphocytic leukemic B cells, as judged by the system-specific synthetic amino acid, 2-amino-2-carboxy-bicyclo (2,2,1)-heptane. This defect was confirmed by studies with two naturally occurring L-system amino acids, leucine and phenylalanine. This specific abnormality of membrane transport by chronic lymphocytic leukemic B lymphocytes is not shared by other B lymphocyte types, and thus appears to be related to the neoplastic nature of the leukemic B cells rather than to their immunologic subtype.

Amino Acids↗
PubMed1984

Calcium exchange and ionized cytoplasmic calcium in resting and activated human monocytes.

We have performed a comprehensive study of calcium tracer flux, distribution, content, and ionized cytoplasmic calcium during monocyte activation. A model of monocyte calcium was developed from 45Ca uptake and exodus curves which indicated that cell calcium was partitioned between three compartments. The magnitude of the time constants for each pool lead us to propose cellular locations for these three compartments: a surface plasma membrane pool, a cytoplasmic pool, and an organelle pool. 45Ca uptake and exodus experiments were analyzed using a nonlinear least squares fit of compartmental exchange rates and sizes. The production of superoxide was used as a reflection of the state of activation of the monocytes treated with Concanavalin A (Con A). We found that Con A-treated monocytes have an increase in the calcium exchange rate with the cytoplasmic pool from 0.04 to 0.07/min (P less than 0.05), and an increase in the size of the cytoplasmic pool from 0.08 to 0.13 pmol/cell (P less than 0.05). There were no significant changes in the exchange rates or sizes associated with either of the other two compartments. The cytoplasmic ionized calcium was measured with the fluorescent probe, Quin 2, which indicated a resting level of 83 nM free calcium in unadhered monocytes. Con A stimulation caused a doubling of the cytoplasmic free calcium to 163 nM within 45 s. This increment in cytoplasmic free calcium preceded the onset of superoxide following Con A treatment. These studies indicate that Con A binding to the plasma membrane increases the monocyte plasma membrane permeability to calcium. External calcium enters the cell at an increased rate and contributes to both internally bound and free calcium. The magnitude of the increase in free calcium is proportional to the concentration of Con A and stimulates calcium extrusion via the calcium transport ATPase. Moreover, there is an increased concentration of ionized cytoplasmic calcium which has the potential to interact with other cellular regulators that modulate cell activation and superoxide production.

Biological Transport, Active↗
PubMed1983

A multicomponent analysis of amino acid transport systems in human lymphocytes. 1. Kinetic parameters of the A and L systems and pathways of uptake of naturally occurring amino acids in blood lymphocytes.

We have determined the kinetic parameters of natural and system-specific synthetic amino acid transport by human blood lymphocytes, using a multi-component computer analysis that separates carrier-mediated uptake from diffusion. These studies were initiated in order to provide the basis for studies of human blood T and B lymphocytes and malignant lymphocytes. Methylaminoisobutyric acid (methyl-AIB) and 2-amino-2-carboxy-bicyclo (2,2,1) heptane (BCH) uptakes into lymphocytes were measured as prototypes of A- and L-system amino acid transport. The Michaelis constant for methyl-AIB uptake was 540 microM; the maximal velocity of uptake was 28 mumol/L cell water/min, and the diffusion coefficient was .004 min-1. In contrast, the Michaelis constant for BCH uptake was 63 microM; the maximal velocity was 969 mumol/L cell water/min, and the diffusion coefficient was .141 min-1. The transport of the naturally occurring amino acids, alanine, proline, and leucine was defined by studies of: (1) competitive inhibition with the system-specific synthetic amino acids, methyl-AIB and BCH, (2) the effect of the transcellular sodium gradient on transport, and (3) evaluation of the time-dependent increase of transport in amino acid-deficient medium (adaptation). Alanine was transported principally (approximately 70%) by the ASC-system, and leucine was transported principally (70%) by the L-system in lymphocytes. The analysis of proline transport was more complex because of a large component of uptake by diffusion even at low amino acid concentrations. Taken together, the kinetics of sodium-sensitive uptake and the results of competitive inhibition studies indicated that proline was transported by the A-system (30%), the ASC system (30%), and also by the L-system (15%).

Amino Acids↗
PubMed1983

The role of calcium in lymphocyte proliferation. (An interpretive review).

A small quantity of extracellular calcium is required for the stimulation of lymphocytes by mitogens such as plant lectins. Lectin binding to the lymphocyte surface and early postbinding events that eventually lead to DNA synthesis are calcium dependent. Mitogenic lectins such as PHA and Con-A rapidly increase the size of an exchangeable pool of cell calcium and cause a smaller rise in intracellular ionized calcium. The increase in ionized calcium is so small (100-200 nM), however, that no increase in total cell calcium is measurable. When lymphocytes are stimulated by a lectin, the rate of calcium entry into the cell increases, but the plasma membrane calcium extrusion pump can prevent the total cell calcium from increasing measurably. The calcium ionophore A23187 is a lymphocyte mitogen and causes an increase in the exchangeable, ionized, and total cell calcium. The former two effects may be causal in mitogenesis; the latter effect is cytotoxic. With A23187 treatment, the rate of calcium influx exceeds the maximum rate of the plasma membrane extrusion pump and cell calcium increases in proportion to the concentration of A23187. The mitochondria, by virtue of their high membrane potential, provide a sink for the buffering of cytoplasmic calcium after A23187 treatment. Thus, the plasma membrane or mitochondria regulate the distribution of lymphocyte calcium when the cell is stimulated by mitogenic lectins or ionophores. The evidence strongly suggests that an alteration in calcium pools or an increase in cytoplasmic ionized calcium plays a role in the initiation of the biochemical reactions that lead to mitogen-induced lymphocyte proliferation in vitro and, perhaps, to the immune response.

B-Lymphocytes↗
PubMed1982

Decreased L-system for amino acid transport in chronic lymphocytic leukemic lymphocytes.

We have defined the kinetic parameters of the L-system of amino acid transport in chronic leukemia of B-lymphocytes (B-cell CLL) and have compared them to those of normal blood lymphocytes, tonsillar lymphocytes, a normal B-lymphocytic cell line (RPMI 1788), and chronic leukemia of T-lymphocytes. The L-system was judged by its affinity for and maximal transport velocity of BCH, a synthetic amino acid whose uptake is virtually limited to the L-system. The L-system of B-cell CLL lymphocytes functioned at less than 15% the rate of the other lymphocyte types, and the substrate affinity of the L-system was lower than that of the other lymphocyte types studied. Thus, the L-system of amino acid transport, a hallmark of normal T- and B-lymphocytes, is vestigial in B-cell CLL. This key functional membrane defect is more closely related to the neoplastic nature of CLL-cells than to their B-lymphocyte phenotype.

Amino Acids↗
PubMed1982

Effects of trifluoperazine and mitogenic lectins on calcium ATPase activity and calcium transport by human lymphocyte plasma membrane vesicles.

The phenothiazine, trifluoperazine, and the mitogenic lectins, phytohemagglutinin (PHA) and Concanavalin A (Con A), were tested for their effects on human lymphocyte plasma membrane Ca-activated Mg-ATPase and ATP-dependent calcium uptake. Trifluoperazine completely inhibited Ca-uptake when present from the start of the assay at concentrations of 100 microM or more. When added during measurement of calcium uptake, trifluoperazine reduced the rate of vesicular calcium accumulation but was unlike the calcium ionophore, A23187, which caused a rapid release of accumulated calcium from the vesicles. Trifluoperazine also inhibited membrane vesicle Ca-ATPase activity, but this inhibition was non-specific since the Mg-ATPase and Na,K-ATPase activities were inhibited to similar extents at the same concentration of the phenothiazine. In contrast, concentrations of PHA and Con A, which are mitogenic for lymphocytes, did not cause any change in Ca-uptake when added to suspensions of membrane vesicles. Con A had no effect and PHA had a weak inhibitory effect on Ca-ATPase activity.

Biological Transport, Active↗
PubMed1982

Plasma membrane vesicles prepared from unadhered monocytes: characterization of calcium transport and the calcium ATPase.

We have purified unadhered human monocytes in sufficient quantities to prepare monocyte plasma membrane vesicles and study vesicular calcium transport. Monocytes were isolated from plateletpheresis residues by counterflow centrifugal elutriation. By combining this source and procedure, 7 x 10(8) monocytes of over 90% purity were obtained. The membranes, isolated on a sucrose step gradient, had an 18-fold enrichment in Na,K-ATPase, a 29-fold diminution of succinate dehydrogenase activity and were vesicular on transmission electron micrographs. The membrane vesicles loaded with oxalate accumulated calcium only in the presence of Mg and ATP. Calcium uptake did not occur if ATP was replaced by any of five nucleotide phosphates or if Mg was omitted. Calcium transport had a maximal velocity of 4 pmoles calcium/micrograms vesicle protein/min and a Km for calcium of 0.53 microM. The ionophore A23187 completely inhibited calcium accumulation while 5 mM sodium cyanide and 10 microM ouabain had no effect. A calcium-activated ATPase was present in the same plasma membrane vesicles. The calcium ATPase had a maximal velocity of 18.0 pmoles calcium/micrograms vesicle protein/min and a Km for calcium of 0.60 microM. Calcium-activated ATPase activity was absent if Mg was omitted or if (gamma - 32P) GTP replaced (gamma - 32P) ATP. Monocyte plasma membranes that were stripped of endogenous calmodulin by EGTA treatment showed a reduced level of calcium uptake and calcium ATPase activity. The addition of exogenous calmodulin restored the transport activity to that of unstripped monocyte plasma membranes. Thus, monocyte plasma membrane vesicles contain a highly specific, ATP-dependent calcium transport system and a calcium-ATPase with similar high calcium affinities.

Adenosine Triphosphate↗
PubMed1981

Calcium transport and calcium-ATPase activity in human lymphocyte plasma membrane vesicles.

We have studied Ca transport and the Ca-activated Mg-ATPase in plasma membrane vesicles prepared from normal human lymphocytes. Membrane vesicles that were exposed to oxalate as a Ca-trapping agent accumulated Ca in the presence of Mg2+ and ATP. ADP, AMP, GTP, UTP, ITP, TTP, or CTP did not substitute for ATP in energizing uptake. The Vmax for Ca uptake was 2.4 pmol of Ca/micrograms of protein/min, and the Km values for Ca and ATP were 1.0 and 80 microM, respectively. One microM A23187, added initially, completely inhibited net Ca uptake and, if added later, caused the release of Ca accumulated previously. Cyanide, oligomycin, ouabain, or varying Na+ or K+ concentrations had no effect on Ca uptake. A Ca-activated ATPase was present in the same membrane vesicles, which had a Vmax of 25 pmol of Pi/micrograms of protein/min at a free Ca concentration of 4-5 microM. This Ca-ATPase had Km values for Ca and ATP of 0.6 and 90 microM, respectively. These kinetic parameters were similar to those observed for uptake of Ca by the vesicles. The Ca-ATPase activity was insensitive to azide, oligomycin, ouabain, or varying Na+ or K+ concentrations. No Ca-activated hydrolysis of GTP or UTP was observed. Both Ca transport and the Ca-ATPase activity of ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid-treated lymphocyte plasma membranes were stimulated 2-fold by a cytoplasmic component (calmodulin) that was purified 500-fold from lymphocyte cytoplasm. Thus, human lymphocyte plasma membranes have both a Ca transport activity and a Ca-stimulated ATPase activity with similar substrate affinities and specificities and similar sensitivities to calmodulin.

Adenosine Triphosphate↗
PubMed1981

Amino acid transport in human lymphocytes: distinctions in the enhanced uptake with PHA treatment or amino acid deprivation.

Human blood lymphocytes increase their concentrative uptake of amino acids when treated with plant lectins such as phytohemagglutinin or when exposed to an amino acid deficient environment (adaptation). Previous studies of the PHA effect have been conducted principally with alpha-aminoisobutyric acid (AIB). We have studied the transport characteristics of naturally occurring amino acids by PHA-treated lymphocytes. These studies have been conducted in the absence and presence of added carrier amino acid to determine whether an increase in transport after PHA treatment is mediated by the same mechanism that occurs during adaptation to a low amino acid environment. PHA stimulated the uptake of AIB, alanine, and proline 1.5- to 2-fold after 4 hours' exposure. AIB and proline, but not alanine transport, also increased when lymphocytes were in an amino acid-deficit medium. When lymphocytes were in an amino acid-deficient medium with PHA, the increase in uptake induced by PHA was superimposed on the increase that occurred in response to an amino acid-deficient medium. Also, PHA stimulated a delayed increase (16--20 hours) in the transport of leucine, whose uptake does not adapt to an amino acid-deficient medium. These data suggest that PHA and amino acid deprivation stimulated rate increases in amino acid transport by separate mechanisms.

Amino Acids↗
PubMed1981

The effect of calcium chelation on lymphocyte monovalent cation permeability, transport and concentration.

We have quantified the effect of EGTA on K exodus and uptake in human blood lymphocytes. When lymphocytes were exposed to a medium containing an EGTA concentration that resulted in an ionized Calcium (Ca) of less than 10 microM, K exodus began to increase. This increase reached nearly threefold that of the control rate in a medium containing sufficient EGTA to reduce the ionized Ca concentration below 0.1 microM. When K exodus was increased, K uptake increased proportionately. This increase in K uptake represented active transport and was associated with an 80% increase in intracellular Na concentration from 15 to 27 mM. The addition of Ca to a medium containing EGTA reversed to normal the increased K exodus and uptake. Histidine, a potent chelator of divalent cations other than Ca, had no effect on K transport. These data indicate that extracellular Ca chelation leads to an increase in lymphocyte membrane permeability and cation leak. This increased leak is associated with an elevation of the cell Na and an increase in transport to a rate equivalent to that of the exodus rate. The compensatory increase in active transport maintains the cell monovalent cation concentration within 10 to 15 mM of unperturbed levels.

Biological Transport, Active↗