Biomedical subjects

R Eckert

Publications and source records attributed to R Eckert.

At least 73 records · Page 4Linked to original sources

PubMed1989

Splenopentin--influence on antibody formation in immunosuppressed animals and on phagocytic capability of human granulocytes.

Sublethally x-ray irradiated C57 Bl/6 Bln. mice (whole body irradiation with 600 cGy) were treated with or without a splenopentin derivative (DA SP-5: N alpha-acetyl-L-arginyl)-(N alpha-acetyl-L-lysyl)-L-glutamyl-L-valyl-L-tyrosine and compared for their capacity to produce antibodies against target sheep red blood cells. As demonstrated DA SP-5 treated mice produced antibodies earlier and in a higher level than animals untreated. Furthermore, DA SP-5 influences the phagocytic capability of human granulocytes in a dose dependent matter.

Animals↗

PubMed1989

[Stimulation of nonspecific immune defense and antibody synthesis with zymosan].

A local sterile inflammation was induced in mice of different inbred strains by means of an i.p. injection of zymosan, a water-insoluble polysaccharide of the cell wall of Saccharomyces cerevisiae. This resulted in a strong enhancement of the unspecific resistance against infections with a LD 90 of gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae and Bordetella bronchiseptica). Furthermore, the treatment with zymosan before or after an immunization with sheep erythrocytes (SE) resulted in a significantly increased specific IgM and IgG primary response in the spleen. However, it was particularly striking that the number of plaque-forming cells against SE was very drastically enhanced in non-immunized mice, in particular cases even up to more than 70 times over the background. Consequently, zymosan possesses immunomodulating effects both on the unspecific resistance and on immune reactions. These results are discussed in relation to the Lyt+-B-cells and an acute phase reaction of B-cells.

Animals↗

PubMed1988

Reversal by interferon-gamma of inhibition of delayed-type hypersensitivity induction by anti-CD4 or anti-interleukin 2 receptor (CD25) monoclonal antibodies. Evidence for the physiological role of the CD4+ TH1+ subset in mice.

In mice, induction of delayed-type hypersensitivity (DTH) and of antibody formation to sheep red blood cells (SRBC) was inhibited by the anti-CD4 monoclonal antibody (mAb) GK1.5. However, anti-interleukin 2 mAb AMT-13 inhibited DTH response but not antibody formation. The inhibitory action of the mAb on DTH, but not an antibody formation, was reversed by concomitant injection of recombinant mouse interferon-gamma. These data provide the first in vivo evidence for the postulated physiological role of the CD4+ TH1 lymphocyte subset and indicate that the action of anti-interleukin 2 receptor mAb is restricted to this T helper subset.

Animals↗

PubMed1988

Modulation of the adoptive immune response in mice by histamine.

The immunomodulatory actions of histamine in mice were examined by a combined in vitro/in vivo approach. Spleen cells from mice were incubated between 2 and 24 hours with histamine (10(-12)-10(-3) M) under conditions which prevent a change of the free histamine concentration. The cells were subsequently transferred to sublethally irradiated syngenic mice in order to measure the adoptive IgM response. Only stimulatory effects of histamine were found at NMRI mice. However, both stimulatory and inhibitory actions were observed at different histamine concentrations if mice of the strains AB or XVII were used. The graft versus host reaction was measured after transfer of histamine treated spleen cells (strain XVII) to neonatal F1 (XVII X B10.LP) hybrid mice and revealed both suppressive and stimulatory effects of histamine at different concentrations. A maximal expression of the immunomodulatory effects of histamine was found after 8 hours of preincubation with the donor cells. The action of selective histamine antagonists and cell separation experiments indicated that the effect of histamine on the adoptive IgM response was mediated by H2-receptors on spleen T-cells. Summarizing, the results indicate that low histamine concentrations elicit bidirectional immunomodulatory effects in mice which vary considerably among different strains.

Animals↗

PubMed1988

Histamine induced murine suppressor and potentiating factors.

Mouse spleen cells were incubated for 24 hours in the presence of histamine (10(-13)-10(-3) M). Aliquots of the histamine free supernatants were intravenously injected into either syngenic or allogenic mice which were subsequently analysed by the Jerne plaque assay in respect of their specific IgM response against red blood cells from sheep. Depending on the histamine concentration during the preincubation and the mouse strain, the effects of the supernatants were found to be suppressive or potentiating. Both the histamine induced suppressor and potentiating factor are generated by T-cells and can be precipitated by (NH4)2SO4. These precipitates were fractionated by gel filtration which revealed a molecular weight of both factors in the range of 20 to 50 kDa. Both lymphokines were found to be sensitive to trypsin, low pH, and heat treatment but were not affected by neuraminidase. They do only interfere with the early events of the IgM response within 24 hours after the administration of the antigen. The conclusion is that the bidirectional modulation of the humoral immune response by histamine in mice is partially due to the induction of these lymphokines by a different efficacy of the histamine receptor activation at different T-cell subsets.

Adjuvants, Immunologic↗

PubMed1988

[Strain dependency of immune reactions in the mouse].

Using three models of immune reactions - the DTH-reaction, the GvH-reaction, and the modulation of immune reactions by histamine - we show that the strain-dependent variability between different inbred strains may exist not only on the quantitative but also on the qualitative level. For many problems it seems necessary to test the suitability of different mouse strains to avoid errors.

Animals↗

PubMed1987

Voltage-activated calcium channels that must be phosphorylated to respond to membrane depolarization.

Two classes of calcium channels were activated by membrane depolarization in cell-free membrane patches from GH3 cells, an electrically excitable cell line derived from a mammalian pituitary tumor. One class had a conductance of approximately 10 pS in 90 mM barium, had a threshold of activation near -40 mV, and was inactivated rapidly at holding potentials more positive than -80 mV. The other class, with a conductance of approximately 23 pS and a threshold nearer -20 mV, did not inactivate in barium but stopped responding to depolarization altogether when the cytoplasmic side of the patch was exposed to a standard physiological saline solution. Buffering the concentration of calcium ions to less than 10 nM on the cytoplasmic side did not prevent this loss of activity. However, activity was restored and maintained for the duration of the patch when the catalytic subunit of cAMP-dependent protein kinase was added with MgATP to the cytoplasmic side of the membrane. Cell-free patch formation in the presence of the dihydropyridine, BAY K 8644, also delayed the loss of activity, but unlike the catalytic subunit plus ATP, BAY K 8644 alone did not restore activity when it was added after the channels no longer responded to depolarization. Evidently the dihydropyridine-sensitive class of voltage-activated calcium channels must be phosphorylated in order to open when the membrane is depolarized. That hypothesis provides a simple framework for understanding the modulation of calcium channel gating by neurotransmitters, calcium ions, and dihydropyridines.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1987

Modulation of potassium conductances by an endogenous neuropeptide in neurones of Aplysia californica.

1. Macroscopic and single-channel currents were recorded from voltage-clamped neurones in the abdominal and pleural ganglia of Aplysia californica in order to investigate conductance changes elicited by application of the endogenous peptide FMRFamide (Phe-Met-Arg-Phe-NH2) and related neuropeptides to the cell surface. 2. The Ca-dependent K current, IK(Ca), when elicited at a constant voltage by intracellular injection of Ca2+, was insensitive to FMRFamide or its derivative YGG-FMRFamide (Tyr-Gly-Gly-Phe-Met-Arg-Phe-NH2). 3. Under steady voltage clamp, certain cells responded to a brief puff of FMRFamide or YGG-FMRFamide with a transient outward current lasting about 1 min. Unclamped cells responded with a corresponding hyperpolarization. These responses reversed at about -75 mV. Ion substitution indicated that the current is carried by K+. 4. FMRFamide and YGG-FMRFamide were equally effective in activating the outward current, whereas FMRF, met-enkephalin and leu-enkephalin were ineffective. 5. At voltages negative to -30 mV and, in the absence of extracellular Ca2+, also at more positive potentials, the FMRFamide-sensitive current showed no voltage dependence beyond that predicted from constant-field considerations. 6. The response to FMRFamide was relatively insensitive to extracellular tetraethylammonium (TEA, KD approximately 75 mM) and 4-aminopyridine (4-AP, KD approximately 6 mM). It was suppressed in Ba-containing solutions, but was unaffected by injection of the Ca chelating agent EGTA. The response was blocked by serotonin and other agents known to elevate intracellular adenosine 3',5'-phosphate (cyclic AMP) levels, and by direct injection of cyclic AMP into the cell. 7. In its pharmacological properties and lack of voltage dependence, the FMRFamide-activated current resembles the 'S' current, IK(S), a K current suppressed by application of serotonin in Aplysia neurones. 8. The similarity between the FMRFamide-sensitive current and the 'S' current was confirmed in cell-attached patch-clamp studies, in which activity of 'S' channels was found to be reduced by serotonin, and enhanced by FMRFamide. 9. Thus, FMRFamide may function in Aplysia to counteract the serotonergic modulation of 'S' channels, which has been proposed as a mechanism of presynaptic plasticity in this mollusc.

4-Aminopyridine↗

PubMed1987

Suppression of calcium current by an endogenous neuropeptide in neurones of Aplysia californica.

1. Actions of the neuropeptide FMRFamide (Phe-Met-Arg-Phe-NH2) and its derivative YGG-FMRFamide (Tyr-Gly-Gly-Phe-Met-Arg-Phe-NH2) on Ca2+ current were examined in identified, voltage-clamped neurones in the abdominal ganglion of Aplysia californica. 2. 'Puffed' application of either peptide at concentrations of 1-50 microM was followed by a transient partial suppression of pharmacologically isolated inward Ca2+ current elicited by a depolarizing step. At 20 degrees C, suppression was maximal 10-25 s following the brief puff of peptide, and lasted up to 90 s. Bath application of peptide had a steady suppressing effect, showing little if any desensitization. 3. Alternative sources of inward current suppression were ruled out, indicating that application of FMRFamide or YGG-FMRFamide produces a true decrease in Ca2+ current, rather than enhancement of possible contaminating outward (K+, H+ or Cl-) currents. 4. FMRFamide and YGG-FMRFamide were equally effective in suppressing Ca2+ current (apparent dissociation constant, KD* approximately 10 microM). However, only 30-50% of the total Ca2+ current elicited by voltage steps to above +10 mV appeared to be susceptible to suppression by even saturating concentrations of peptide. This, as well as a reduced effect of the peptides on Ca2+ current which was observed at potentials below +10 mV, may perhaps result from the presence of more than one class of Ca2+ channels, only one of which is sensitive to FMRFamide. 5. FMRFamide eliminated a constant fraction of Ca2+ current at all potentials above +10 mV, and had no direct effect on activation or inactivation of the remaining current. This behaviour is consistent with reduction in the number of functional Ca2+ channels by the peptide. 6. Suppression of Ca2+ current produced a concomitant depression of Ca2+-dependent K+ current, which was shown previously to be insensitive to FMRFamide when activated by direct ionophoretic injection of Ca2+ into the cell. 7. The effect of FMRFamide on Ca2+ current was normal following interference with or activation of known second-messenger systems, those involving adenosine 3',5'-cyclic monophosphate (cyclic AMP), cyclic GMP, Ca2+, inositol trisphosphate and protein kinase C. 8. Suppression of Ca2+ current by FMRFamide appeared to be mediated by the same receptor as enhancement by the peptide of K+ current resembling IK(S) (K+ current suppressed by serotonin), an effect seen in most of the same cells. Both effects of FMRFamide were mimicked by injection of guanosine 5'-O-(3-thiotriphosphate) (GTP-gamma-S) into the cell, suggesting that the peptide may exert its effects by activating a guanosine 5'-triphosphate (GTP)-binding protein

Action Potentials↗

PubMed1987

Changes in the intracellular free calcium concentration of Aplysia and leech neurones measured with calcium-sensitive microelectrodes.

The intracellular free Ca concentration was measured in invertebrate neurones using single-barrelled and double-barrelled neutral-carrier microelectrodes. The electrodes were calibrated in solutions containing different Ca concentrations between 1 mM and 0.01 microM. The electrode responses were also tested at different ionic strengths and at varying Na concentrations. The electrodes responded with 25-30 mV per 10-fold change in Ca concentration between 1 mM and 1 microM and with 10-25 mV between 1 and 0.1 microM Ca. The intracellular free Ca concentration was measured to be between 0.1 and 0.7 microM in the neurones. The changes of intracellular Ca in identified voltage-clamped neurones of Aplysia californica were recorded during iontophoretic injections of Ca2+ or EGTA. The decrease of intracellular Ca following EGTA injection was correlated with the suppression of the Ca-dependent K current and with the reduction of Ca-induced inactivation of voltage-dependent Ca current. In identified neurones of the leech Hirudo medicinalis a reversible increase of intracellular Ca2+ was recorded after inhibition of the Na-K pump, either by addition of ouabain (0.5 mM) or by lowering the external K concentration (0.2 mM). This rise in intracellular Ca2+ did not occur, and was even reversed, in the absence of external Na, suggesting the existence of Na-Ca exchange across the leech neuronal membrane.

Animals↗

PubMed1986

Effect of splenopentin (SP-5) on the antibody formation in immunosuppressed mice.

Sublethally irradiated C57Bl/6 mice (whole body irradiation with 600 cGy) were treated with or without diacetyl splenopentin and compared for their capacity to produce antibodies against target sheep red blood cells. As demonstrated, mice treated with splenopentin produced antibodies earlier and in a higher level than animals untreated.

Animals↗

PubMed1986

An enzymatic mechanism for calcium current inactivation in dialysed Helix neurones.

'Wash-out' and inactivation of the Ca current were examined in dialysed, voltage-clamped neurones of Helix aspersa under conditions that isolate the Ca current virtually free of other currents. EGTA or other internal Ca2+ chelators were routinely omitted from the dialysate. The time-dependent loss, or wash-out, of Ca current was slowed by addition to the dialysing solution of agents, such as dibutyryl adenosine 3'-5'-cyclic monophosphate (dibutyryl cyclic AMP), Mg adenosine 5'-triphosphate (ATP) and the catalytic subunit of cyclic-AMP-dependent protein kinase, that promote protein phosphorylation and by EGTA. However, neither the phosphorylation-promoting agents nor internal EGTA prevented wash-out entirely, nor did they significantly restore previously 'washed-out' current. With phosphorylating agents in the dialysing solution, the irreversible development of wash-out was greatly reduced by introduction of leupeptin, an inhibitor of protease activity. Thus, the irreversible component of wash-out appears to result from a Ca-dependent proteolytic process. In the presence of leupeptin alone, Ca current amplitude continued to decline: however, the current could be largely or fully restored with addition of catalytic subunit, dibutyryl cyclic AMP, and Mg ATP to the dialysing solution. Thus, inhibition of proteolysis revealed a reversible component of wash-out that appears to result from dephosphorylation. During perfusion with leupeptin, Mg ATP, dibutyryl cyclic AMP and catalytic subunit the Ca current remained stable for up to several hours without addition of internal Ca2+ buffer. The rate of inactivation of the current that occurs during a depolarizing step showed only a very gradual decline during this time. Under these conditions, perfusion with calcineurin, a Ca-calmodulin-dependent phosphatase, caused a significant increase in the rate of Ca current inactivation. This inactivation was virtually eliminated by introduction of EGTA or by replacement of external Ca2+ with Ba2+, which is consistent with the ion dependency for calmodulin-dependent activation of calcineurin. When ATP in the dialysate was replaced with ATP-gamma-S (adenosine 5'-O-(thiotriphosphate], an analogue that donates a thiophosphate group resistant to hydrolysis, the rate of inactivation slowed. Since Ca-dependent inactivation during step depolarizations is enhanced by conditions that promote dephosphorylation, and Ca current wash-out is slowed by conditions that promote phosphorylation, inactivation and reversible wash-out appear to be related.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

PubMed1986

[Histamine receptor-bearing lymphocytes. VI. Influence of histamine on the Go-G1 transition of activated lymphocytes].

Histamine (10(-4) M) suppressed the PHA-induced activation of lymphocytes in vitro. This was shown by inhibition of the expression of DR- and 4F2-antigens, of the blast transformation, DNA- and RNA-synthesis, and the formation of thermostable sheep erythrocyte rosettes. Histamine affect these phenomenons only when added to the culture during the first hours. Already 6 hrs after addition of PHA, it exerted no significant suppression. The target of the inhibiting effect of histamine is the G0-G1-transition of the lymphocytes. Cells that already had entered the G1-phase were no more susceptible to histamine.

Animals↗

PubMed1986

Enzymatic regulation of calcium current in dialyzed and intact molluscan neurons.

Isolated neurons of Helix aspersa were dialyzed and voltage clamped under conditions that isolate the Ca current. The rapid time-dependent run-down, or washout, of Ca current could be slowed by addition of 1 mM EGTA to the dialysis solution. A more effective means of slowing washout was the use of agents that promote protein phosphorylation, such as cAMP, Mg-ATP and the catalytic subunit (CS) of cAMP-dependent protein kinase, along with leupeptin, a tripeptide inhibitor of proteases. In the presence of these agents, no internal EGTA was required to prevent Ca current washout. Thus, during dialysis with 100 microM leupeptin, 7 mM Mg-ATP and 20 micrograms/ml CS, the Ca current remained stable for up to several hours. The rate of Ca-dependent inactivation of the current that occurs during a depolarizing step showed only a small decline during prolonged dialysis. Under these conditions, introduction of 10 microM calmodulin plus 40 micrograms/ml calcineurin, a Ca-calmodulin-dependent phosphatase, caused a significant increase in the rate of Ca current inactivation during a depolarizing step. This increase in rate of inactivation, as well as the original inactivation, was eliminated by introduction of EGTA or replacement of external Ca with Ba, results that are consistent with the ion dependency for activation of calcineurin. When internal ATP was replaced with ATP-gamma-S, a hydrolysis-resistant analogue, the rate of Ca current inactivation slowed, providing further evidence that inactivation involves a dephosphorylation.(ABSTRACT TRUNCATED AT 250 WORDS)

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed1986

[Histamine receptor-bearing lymphocytes. V. Induction of suppressor cells with histamine or concanavalin A].

Immature human T-lymphocytes form rosettes with autologous erythrocytes (A-RFC). Con A induced suppressor cells in fractions of A-RFC. Mature, immunocompetent T-lymphocytes are non-A-RFC. They bear histamine receptors, and in such fractions histamine induced suppressor cells. After activation, both suppressor cells seem to be identical. They bear histamine receptors, Fe-receptors for IgG and the T8-antigen. For the expression of their suppressive effect the presence of monocytes is required.

Animals↗

PubMed1986

[Histamine receptor-bearing lymphocytes. VII. Antibody formation and graft-vs-host reaction from spleen cells after separation on histamine affinity columns].

Histamine-ovalbumin conjugates were characterized in respect to the relative amount of histamine residues which are accessible to membrane receptors. These conjugates were bound to a protein carrier. Spleen cells exhibited an enhanced reactivity in the adoptive antibody production as well as the graft versus host reaction after filtration through affinity columns with a low density of histamine residues. Contrary to that, the use of affinity columns with high histamine density led to a reduced immunoreactivity of the nonadherent cells. Consequently, controversial literature data concerning this problem seem to be based on methodological differences. The results support the hypothesis, that suppressor cells carry more histamine receptors than other immunoreactive cells.

Animals↗

PubMed1986

Histamine receptor-bearing lymphocytes (HRL). VIII. Splenopentin-accelerated reconstitution of the immunoresponsiveness after elimination of HRL.

The maturation effect of DA-SP5 on a spleen cell population depleted of immunocompetent, histami nereceptor-bearing lymphocytes was examined. Conjugates of histamine and the A-chain of the mistletoe lectin I killed in vitro these cells and abolished, as shown in a previous paper, their humoral and cellular capacity by around 90%. Sublethally irradiated mice were reconstituted with the remaining cells and treated with DA-SP5 (3 intraperitoneally injections of 10 micrograms DA-SP5 per week). The strong accelerating action of DA-SP5 on the restoration of the antibody response is interpreted as an effect of DA-SP5 on the maturation of B- and T-cells under in vivo conditions.

Animals↗

PubMed1986

Histamine as endogenous immunomodulator.

Histamine induces the T-cell dependent production of both suppressive and enhancing factor via its interaction with H2-receptors. This could be shown by the transfer of cells or crude lymphokine preparations after in vitro histamine treatment into recipient mice, which were characterized with respect to their humoral immune response. The effective histamine concentrations differed remarkably among different mouse strains which indicates a complex regulatory network. The combined in vitro/in vivo approach as performed in these experiments leads to the conclusion that histamine may act as a suppressive as well as an enhancing immunomodulator on the humoral immune response in vivo.

Animals↗