Cytosolic free calcium in chick heart cells. Its role in cell injury

The role of cytosolic free Ca2+ (Caf) in cell injury was investigated using two methods for measuring Caf in freshly disaggregated embryonic chick heart cells. The null-point method, using arsenazo III, is based on determining the extracellular Ca2+ concentration at which no net Ca2+ movement occurs when plasma membrane permeability is increased. With this technique, the null point Caf averaged 0.23 +/- 0.07 microM (n = 6) in the basal state. Using quin2, an intracellular fluorescent dye, to measure Caf a value of 0.05 +/- 0.01 microM (n = 5) was obtained. Elevation of Caf by various agents was associated with an increase in cell injury as measured by the release of the cytosolic enzyme, LDH. However, the relationship between Caf and LDH release was not a direct one under all experimental conditions, indicating that the level of Caf is not the sole determinant of cell injury.

Na/H exchange in cultured chick heart cells. pHi regulation

The purpose of this study was to establish the existence of Na/H exchange in cardiac muscle and to evaluate the contribution of Na/H exchange to pHi regulation. The kinetics of pHi changes in cultured chick heart cells were monitored microfluorometrically with 6-carboxyfluorescein and correlated with Nai content changes analyzed by atomic absorption spectrophotometry; transmembrane H+ movements were evaluated under pH stat conditions. After induction of an intracellular acid load by pretreatment with NH4Cl, a regulatory cytoplasmic alkalinization occurred with a t1/2 of 2.9 min. pHi regulation required external Na+ and was concomitant with transmembrane H+ extrusion as well as a rapid rise in Nai content in an Na/H ratio of 1:1. Microelectrode recordings of membrane potential demonstrated directly the electroneutral character of pHi regulation. Acid-induced net Na+ uptake could be either stimulated by further decreasing pHi or inhibited by decreasing pHo; Na+ uptake was unaffected by tetrodotoxin (10 micrograms/ml), quinidine (10(-3) M), DIDS (10(-4) M), Clo-free solution, or HCO3-free solution. Amiloride (10(-3) M) maximally inhibited both pHi regulation and Na+ uptake; the ID50 for amiloride inhibition of Na+ uptake was 3 microM. Nao-dependent H+ extrusion showed half-maximal activation at 15 mM Nao; Li+, but not K+ or choline+, could substitute for Na+ to support H+ extrusion. Cao-free solution also stimulated acid-induced Na+ uptake. We conclude that pHi regulation following an acid load in cardiac muscle cells is by an amiloride-sensitive, electroneutral Na/H exchange. Stimulation of Na/H exchange up to 54 pmol/cm2 X s indicates the rapidity of this exchange across cardiac cell membranes. Na/H exchange may also participate in steady state maintenance of pHi.

Patterns of thymocyte differentiation markers on virus and radiation induced lymphomas of C57BL/Ka mice

To better understand the biology of tumorigenesis in virus and radiation lymphomas of C57Bl/Ka mice, we have examined the cell surface phenotypes of a large series of primary tumors induced by both agents. Data derived using flow cytometry and recently available monoclonal antibodies to thymocyte differentiation antigens supports three major conclusions. First, tumor cell populations are unimodal for staining with most antibodies and are probably of clonal origin. Second, many, but not all, tumor cells show surface phenotypes similar to those of previously defined subpopulations of normal thymocytes. Third, at the cell surface level, no major differences between virus- and radiation-induced lymphomas can be discerned. Our data thus further define the relationship between thymomas induced by these two agents.

Prevalence of mandibular dysfunction in 10-18 year old Israeli schoolchildren

The prevalence of mandibular dysfunction in a sample of 369 Israeli schoolchildren was found to be 56.4%, indicating that one or more of the cardinal symptoms were present. It increased with age from about 51% in the 10-13 year old group to 67.8% in the 16-18 year olds. The most common cardinal sign of dysfunction was joint sounds (35.8%), which increased with age from 28% in the youngest group to 44.3% in the oldest group. The second most common sign was joint sensitivity to palpation (30.4%), which showed a slight increase in the oldest group. Sensitivity of the superficial muscles was recorded third, with 20%. Joint pain and restriction of mandibular movement appeared infrequently. Two of the more common cardinal symptoms, namely joint sounds and muscle sensitivity, were statistically related to several possible aetiological factors and to age and sex. Analysis of association showed that the probability of muscle sensitivity increased in the presence of malocclusion and/or joint sensitivity to palpation. It also showed that age, occlusal wear, locking of the jaw and joint sensitivity to palpation increased the probability of joint sounds.

Demonstration of uronic acid capsular material in the cerebrospinal fluid of a patient with meningitis caused by mucoid Pseudomonas aeruginosa

A 39-year-old female with insulin-dependent diabetes mellitus developed Rhizopus infection of the maxillary sinus. Subsequent to successful treatment with amphotericin B and surgical debridement, she developed purulent meningitis due to a mucoid strain of Pseudomonas aeruginosa. Analysis of cerebrospinal fluid documented the presence of a uronic acid polymer at a concentration of 40 micrograms/ml. In spite of parenteral and intrathecal antibiotic therapy, the patient died. This case illustrates that mucoid strains of P. aeruginosa may result in fatal infection and that alginate capsule is produced in vivo in humans.

Theoretical effects of transmembrane electroneutral exchange on membrane potential

Transmembrane electroneutral transport mechanisms [e.g., Na/H exchange, Cl/HCO3 exchange, (K + Cl) cotransport] have recently been identified in a wide variety of cell types. If these exchanges sum to give a net electroneutral Na/K exchange, they may hyperpolarize the membrane potential beyond the value calculated from the Mullins-Noda equation, provided the cell maintains steady state intracellular ionic concentrations. In extreme circumstances, the membrane potential could hyperpolarize beyond the potassium reversal potential. This effect is mediated by the electrogenic Na/K pump. If either Na or K exchanges electroneutrally against a third ion (e.g., Na/Ca exchange), then the exchange may depolarize the membrane potential.

Calcium elevation in cultured heart cells: its role in cell injury

Inhibition of the Na+-K+ pump in cultured embryonic chick heart cells promotes the elevation of intracellular Ca2+ and is a useful manipulation to study the relationship between Ca2+ and myocardial cell injury. One hour of Na+-K+ pump inhibition resulted in a fourfold increase in cell Na+, a 50% decline in cell K+, and a 5- to 10-fold increase in cell Ca2+, 45% of which is mitochondrial. The degree of cell injury induced by Ca2+ loading was evaluated by monitoring the content of adenosine 5'-triphosphate (ATP) and the release of the intracellular enzyme lactate dehydrogenase (LDH). Under these conditions ATP content declined by 25-30% and LDH release increased from 1 to 1.4% of the total LDH. Furthermore, cells subjected to 1 h of Na+-K+ pump inhibition and returned to control solution for 5 h showed that Ca2+ decreased to near control levels and ATP content was restored. Although inhibition of Na+-K+ transport caused a large increase in cell Ca2+, neither Na+-K+ pump inhibition nor elevation in total cell Ca2+ per se resulted in irreversible myocardial cell injury.

A note on the reactivation of the fast sodium current in spherical clusters of embryonic chick heart cells

Reactivation of the fast sodium current in spherical clusters of embryonic chick heart cells was studied using the two-microelectrode voltage-clamp technique. The results show that there are at least two phases of reactivation. The contribution of the two phases to the overall reactivation process is highly dependent on the particular pulse protocol used to measure them.

Transmembrane chloride flux in tissue-cultured chick heart cells

To evaluate the transmembrane movement of chloride in a preparation of cardiac muscle lacking the extracellular diffusion limitations of natural specimens, intracellular chloride concentration ( [Cl] i) and transmembrane 36Cl efflux have been determined in growth-oriented embryonic chick heart cells in tissue culture. Using the method of isotopic equilibrium, [Cl]i was 25.1 +/- 7.3 mmol x (liter cell water)-1, comparable to the value of 24.9 +/- 5.4 mmol x (liter cell water)-1 determined by coulometric titration. Two cellular 36Cl compartments were found; one exchanged with a rate constant of 0.67 +/- 0.12 min-1 and was associated with the cardiac muscle cells; the other, attributed to the fibroblasts, exchanged with a rate constant of 0.18 +/- 0.05 min-1. At 37 degrees C, transmembrane Cl flux of cardiac muscle under steady-state conditions was 30 pmol x cm-2 x s-1. In K-free, normal, or high-Ko solutions, the responses of the membrane potential to changes in external Cl concentration suggested that chloride conductance was low. These results indicate that Cl transport across the myocardial cell membrane is more rapid than K transport and is largely electrically silent.

Microfluorometric monitoring of pHi in cultured heart cells: Na+-H+ exchange

Continuous measurement of intracellular pH (pHi) should enhance the likelihood of defining the mechanisms of pHi regulation in actively contracting preparations of cardiac muscle. A filter microfluorometric technique was adapted for use with growth-oriented embryonic chick heart cells to continuously monitor changes in the fluorescence intensity of the pH-sensitive chromophore 6-carboxyfluorescein, generated in situ. Data pertaining to the direction and the rate of pHi changes assisted in thermodynamically characterizing and ascertaining net kinetic parameters of a Na+-H+ exchange mechanism. Imposing an outward Na+ gradient across the cardiac cell membrane rapidly (t 1/2 = 44 s) induced cytosolic acidification, whereas an inward Na+ gradient produced cytosolic alkalinization (t 1/2 = 40 s). Amiloride (10(-3) M) caused the cytoplasm to acidify (t 1/2 = 46 s) and also reversibly blocked the acidification induced by low extracellular Na+. These results are consistent with the presence of a rapid Na+-H+ exchange mechanism in the cardiac cell membrane. Further investigations are required to characterize the involvement of Na+-H+ exchange in pHi regulation and to differentiate the effects of Na+-H+ exchange from other ion gradient-coupled mechanisms, e.g., Na+-Ca2+ exchange.

Pool size of pluripotential hematopoietic stem cells increased in continuous bone marrow culture by Friend spleen focus-forming virus

Continuous mouse bone marrow cultures were infected with Friend murine leukemia virus. Production of nonadherent (NA) and adherent cells, granulocyte-macrophage colony-forming unit(s) of progenitor cells (GM-CFUc), pluripotential hematopoietic stem cells (CFUs), the self-renewal potential (Rs) of CFUs, and generation of factor-dependent (FD) multipotential and committed permanent stem cell cloned lines were measured. Uninfected marrow cultures from C57BL/6J, C57BL/6JUt, B6.S, C3H/HeJ, (C57BL/6J x DBA/2J)F1, CD- 1 Swiss, or N:NIH(S) mice generated NA cells, GM-CFUc, and CFUs for 20-41 weeks; cultures infected with Rauscher or other helper viruses generated them for 35-45 weeks. GM-CFUc and CFUs production in SFFV-positive cultures persisted for over 65 weeks and exceeded control levels by twentyfold to fiftyfold. The Rs of CFUs in SFFV-positive cultures was not detectably increased above control cultures. Multipotential (erythroid-neutrophil-mast cell-basophil-eosinophil) permanent FD cell clones were derived from control and SFFV-positive cultures. Thus SFFV amplifies the stem cell pool in vitro without detectably increasing the Rs capacity of CFUs.

Presentation of Academy Plaque to Joseph Post, M.D

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Inhibition by polyamines of macromolecular synthesis and its implication for ethylene production and senescence processes

Applied diamines and polyamines inhibited the incorporation of radioactively labeled leucine and uridine into trichloroacetic acid-insoluble material in apple (Malus domestica Borkh, cv Golden Delicious) fruit tissue. The inhibitory effect was in general more pronounced with the higher molecular weight amines. Putrescine at 5 millimolar inhibited leucine incorporation by 37% and uridine by 44%. Spermidine and spermine at the same concentration inhibited uridine incorporation by 60%. The polyamines at concentrations between 0.1 and 1.0 millimolar inhibited leucine incorporation by 55 to 90%. The inhibitory effect of 0.1 to 10 millimolar polyamines on dark- and wound-induced senescence or ethylene production, is discussed in the light of interference with macromolecular synthesis.

Sodium tracer kinetics and transmembrane flux in tissue-cultured chick heart cells

Considerable difficulty has been encountered in defining the physiological significance of sodium tracer kinetic measurements in cardiac muscle. In this study, 24Na+ efflux experiments were performed by directly monitoring tissue radioactivity during the superfusion of growth-oriented embryonic chick heart cells in tissue cultured. The cellular 24Na+ efflux from contractile preparations exhibited at least two exponential components whereas noncontractile, fibroblastlike preparations had a single efflux component similar in rate to the slower component of the contractile preparations. We concluded that the slow component represents efflux from nonmuscle cells, whereas the faster component reflects the muscle cell compartment. The mean Na+ efflux rate constants for contractile preparations (beating 150 min-1) were 3.1 and 0.35 min-1. Intracellular Na+ concentrations, as determined by isotope uptake and by flame photometry, were 18 and 16 mM for contractile and nonmuscle preparations, respectively. The steady-state, transmembrane fluxes are 98 and 5 pmol . cm-2 . s-1 for muscle and nonmuscle cells, respectively. The Na+ efflux kinetics in 10(-4) M ouabain were reduced by approximately 16% from the control value. These findings indicate that the greater part of the steady-state Na+ efflux in cultured heart cells is due to mechanisms other than the Na+-K+ pump.

Recycling of 5'-methylthioadenosine-ribose carbon atoms into methionine in tomato tissue in relation to ethylene production

The ribose moiety of 5'-methylthioadenosine (MTA) is metabolized to form the four-carbon unit (2-aminobutyrate) of methionine in tomato tissue (Lycopersicon esculentum Mill., cv. Pik Red). When [U-(14)C-adenosine] MTA was administered to tomato tissue slices, label was recovered in 5-methylthioribose (MTR), methionine, 1-aminocyclopropane-1-carboxylic acid (ACC), C(2)H(4) and other unidentified compounds. However, when [U-(14)C-ribose]MTR was administered, radioactivities were recovered in methionine, ACC and C(2)H(4), but not MTA. This suggests that C(2)H(4) formed in tomato pericarp tissue may be derived from the ribose portion of MTA via MTR, methionine and ACC. The conversion of MTR to methionine is not inhibited by aminoethoxyvinylglycine (AVG), but is O(2) dependent. These data present a new salvage pathway for methionine biosynthesis which may be important in relation to polyamine and ethylene biosynthesis in tomato tissue.

Delivery of the second twin

A retrospective chart review of all twin deliveries between April 1, 1977, and March 20, 1980, at the Boston City Hospital and the Brigham and Women's Hospital revealed corrected neonatal mortality rates of 0 for 74 twins in nonvertex presentation delivered by cesarean section and 0 for 76 second-born twins extracted vaginally. Breech extraction of 76 second-born twins weighing more than 1499 g at birth was not associated with a statistically significant increase in the incidence of 5-minute Apgar scores of 7 or less when compared to 74 similarly asymptomatic twins in nonvertex presentation delivered by cesarean section. Vaginal delivery may be considered when the second twin, weighing more than 1500 to 2000 g, is in breech presentation.

Influence of calcium and magnesium on ethylene production by apple tissue slices

The decline in ethylene production in apple (Pyrus malus L. cv. Golden Delicious) tissue slices during 24 hours incubation in 600 millimolar sorbitol and 10 millimolar 2-(N-morpholino)ethanesulfonic acid buffer (pH 6.0) is recognized as a senescent phenomenon. The inclusion of very high concentrations (100 millimolar) of Ca(2+), Mg(2+), or Ca(2+) plus Mg(2+) severely inhibited ethylene production during the first 6 hours of incubation. However, after 6 hours and up to 24 hours the ethylene-forming system was stablized. These high concentrations of Ca(2+), Mg(2+), or Ca(2+) plus Mg(2+) virtually eliminated lipid peroxidation and protein leakage from these slices. Also conversion of 1-aminocyclopropane-1-carboxylic-1-acid to ethylene and the influence of indoleacetic acid on ethylene production was stabilized after 24 hours of incubation by these high concentrations of Ca(2+), Mg(2+), and Ca(2+) plus Mg(2+). Addition of divalent ionophores severely inhibited ethylene production, but this inhibition was prevented by Ca(2+) in concentrations greater than the ionophore. These data suggest that the loss of ethylene production by aging tissue slices results from degradation of membranes. They support previous work that indicates that the ethylene-forming system, perhaps the segment of the pathway from 1-aminocyclo-propane-1-carboxylic-1-acid to ethylene, resides in the plasma membrane.

Biosynthesis of ethylene from methionine in aminoethoxyvinylglycine-resistant avocado tissue

This study was conducted to determine if aminoethoxyvinylglycine (AVG) insensitivity in avocado (Persea americana Mill., Lula, Haas, and Bacon) tissue was due to an alternate pathway of ethylene biosynthesis from methionine. AVG, at 0.1 millimolar, had little or no inhibitory effect on either total ethylene production or [(14)C] ethylene production from [(14)C]methionine in avocado tissue at various stages of ripening. However, aminoxyacetic acid (AOA), which inhibits 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (the AVG-sensitive enzyme of ethylene biosynthesis), inhibited ethylene production in avocado tissue. Total ethylene production was stimulated, and [(14)C]ethylene production from [(14)C]methionine was lowered by treating avocado tissue with 1 millimolar ACC. An inhibitor of methionine adenosyltransferase (EC 2.5.1.6), l-2-amino-4-hexynoic acid (AHA), at 1.5 millimolar, effectively inhibited [(14)C]ethylene production from [(14)C]methionine in avocado tissue but had no effect on total ethylene production during a 2-hour incubation. Rates of [(14)C]AVG uptake by avocado and apple (Malus domestica Borkh., Golden Delicious) tissues were similar, and [(14)C]AVG was the only radioactive compound in alcohol-soluble fractions of the tissues. Hence, AVG-insensitivity in avocado tissue does not appear to be due to lack of uptake or to metabolism of AVG by avocado tissue. ACC synthase activity in extracts of avocado tissue was strongly inhibited (about 60%) by 10 micromolar AVG. Insensitivity of ethylene production in avocado tissue to AVG may be due to inaccessibility of ACC synthase to AVG. AVG-resistance in the avocado system is, therefore, different from that of early climacteric apple tissue, in which AVG-insensitivity of total ethylene production appears to be due to a high level of endogenous ACC relative to its rate of conversion to ethylene. However, the sensitivity of the avocado system to AOA and AHA, dilution of labeled ethylene production by ACC, and stimulation of total ethylene production by ACC provide evidence for the methionine --> SAM --> ACC --> ethylene pathway in avocado and do not suggest the operation of an alternate pathway.

Phenotypic characterization of mice of thymus target cells susceptible to productive infection by the radiation leukemia virus

The spread of virus replication was studied by electron microscopy in the thymuses of inbred C57BL/Ka mice after intrathymic inoculation of the radiation leukemia virus (RadLV). The first type C-budding virus particles appeared in scarce blast cells of the subcapsular zone. Most of these blast cells were "X-cells," i.e., the thymus lymphoid cells most actively engaged in DNA synthesis. Virus replication spread to the entire cortical blast cell population and, from day 7 on, to the small cortical lymphocytes. The first virus-producing cells were derived from a very few target cells (approximately 0.001-0.003% of thymocytes) susceptible to RadLV infection. For determination of the phenotypes of these target cells, various thymocyte subpopulations obtained through a battery of cell separation methods were tested for their ability to support the replication of RadLV/VL3 virus in short-term culture. Most of these target cells were sensitive to the lytic effect of hydrocortisone and migrated in the fastest fraction of a 1Xg sedimentation gradient, together with the majority of [3H] thymidine-incorporating blast cells. They exhibited an intermediate density and expressed H-2 and Thy 1,2 cell surface antigens, although they were not found preferentially among the high Thy 1,2 population to which most of the cortical blast cells belonged. The spread of RadLV within the thymus and the surface phenotype characteristics of target cells indicate that these cells correspond to the thymocyte subset at the earliest stage of thymic lymphopoiesis and may be transitional between the prothymocytes and the subcapsular blast cell population.

Linear electrical properties of passive and active currents in spherical heart cell clusters

Impedance studies were performed on small spherical clusters of embryonic chick heart cells grown in tissue culture. Each syncytial cluster was impaled with two microelectrodes; one injected low amplitude stochastic current and the other recorded the resulting perturbation of intracellular potential. The current and potential records were digitized, decomposed into their sinusoidal components, and the frequency domain impedance of the cluster was determined. The impedance data were compared with a theory for current flow in a spherical syncytium and values were derived for parameters describing the membranes and intercellular clefts of the tissue. The clusters were spontaneously active but usually became temporarily quiescent when impaled with two electrodes. The potential stabilized at a value close to -30 mV. At this depolarized potential, active slow currents, presumably present in the cardiac action potential, contributed noticeably to the linear impedance, producing a resonant peak in the magnitude of the impedance at a frequency of 1-3 Hz. The linearized impedance functions for these currents were characterized in the presence and absence of tetrodotoxin (TTX) and D-600. TTX had no noticeable effect on the impedance but D-600 essentially abolished the active currents. Although the ionic basis of these currents is not known, frequency domain analysis appears to be a viable technique for studying slow currents in heart muscle.