Biomedical subjects

K Gottmann

Publications and source records attributed to K Gottmann.

34 records · Page 2Linked to original sources

PubMed1994

The formation of glutamatergic synapses in cultured central neurons: selective increase in miniature synaptic currents.

The formation of synapses between cultured rat thalamic neurons was studied with electrophysiological and immunocytochemical methods. Thalamic neurons in culture form predominantly glutamatergic synapses. Already after 3 days in vitro glutamatergic miniature EPSCs occurred spontaneously and their frequency was strongly increased after K+ depolarization, while GABAergic mIPSCs were found after K+ depolarization at lower frequency. This demonstrates that both, excitatory glutamatergic and inhibitory GABAergic synapses were functional in close succession to initial neurite outgrowth. Synapses formed independent of spontaneous electrical activity, which was absent during the first week in culture. Spontaneous action potentials appeared during the second week and chronic action potential blockade by addition of tetrodotoxin reduced neuronal survival and the number of glutamatergic synapses per neuron. During in vitro differentiation the number of synapsin I immunoreactive presynaptic terminals and the frequency of spontaneous glutamatergic miniature EPSCs increased closely correlated, while the frequency of GABAergic mIPSCs after K+ depolarization did not increase. Thus, the continous formation of presynaptic terminals, including possible maturation of transmitter release, appeared to underlie the increase in mEPSC frequency. Analysis of miniature EPSC amplitudes at different stages in vitro revealed an increase in amplitudes, suggesting synaptic differentiation after initial establishment of functional transmission in glutamatergic synapses. This process was synapse specific as amplitudes of GABAergic mIPSCs were invariant.

Action Potentials↗

PubMed1994

Kinetics of GABAB receptor-mediated inhibition of calcium currents and excitatory synaptic transmission in hippocampal neurons in vitro.

The time courses of the gamma-aminobutyric acid type B (GABAB) receptor-mediated inhibition of excitatory synaptic transmission and of action potential-evoked calcium currents were studied in hippocampal neurons in vitro with step-like changes of a saturating baclofen concentration. Inhibition mediated by postsynaptic GABAB receptors was excluded pharmacologically. Both presynaptic inhibition and reduction of calcium currents developed and declined exponentially with similar time constants of about 0.2 and 3 s, respectively. The close correlation of the time courses indicates that fast, G protein-mediated depression of voltage-gated calcium channels and thus direct reduction of the presynaptic calcium influx may contribute to the GABAB receptor-induced inhibition of excitatory synaptic transmission in hippocampal neurons in vitro.

Action Potentials↗

PubMed1992

Evans blue reduces macroscopic desensitization of non-NMDA receptor mediated currents and prolongs excitatory postsynaptic currents in cultured rat thalamic neurons.

Fast application of L-glutamate, AMPA (alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid) or kainate to cultured rat thalamic neurons revealed properties of non-NMDA (N-methyl-D-aspartate) receptors similar to those described in hippocampal neurons. The kinetics of non-NMDA receptor-mediated currents were altered by the addition of the dye Evans Blue (EB). Macroscopic desensitization was reduced and activation and deactivation kinetics were slowed. Delayed addition of EB, after desensitization of non-NMDA receptors, resulted in reactivation of desensitized receptors. Thus, both ion channel gating and entry into the desensitized state were affected. Evans blue also slowed the activation and the decay of glutamatergic miniature EPSCs (excitatory postsynaptic currents), demonstrating that receptor kinetics determine the time course of the synaptic response.

Animals↗

PubMed1992

Pharmacological characterization of calcium currents and synaptic transmission between thalamic neurons in vitro.

We recorded from pairs of cultured, synaptically connected thalamic neurons. Evoked excitatory postsynaptic currents (EPSCs) reversed at +17 mV and were blocked reversibly by 1 mM kynurenic acid, a glutamate receptor antagonist. NMDA and non-NMDA receptors mediated excitatory post-synaptic responses, as shown by selective block of EPSC components with 50 microM (+/-)-2-amino-5-phosphonopentanoic acid and 10 microM 6,7-dinitroquinoxaline-2,3-dione, respectively. Inhibitory postsynaptic responses were evoked less frequently and were blocked by the GABAA receptor antagonist (-)-bicuculline methochloride. The pharmacological profiles of whole-cell calcium currents and evoked EPSCs were compared. With 50 microM cadmium chloride (Cd), whole-cell low voltage-activated (LVA) calcium currents were reduced in amplitude and high voltage-activated (HVA) calcium currents and excitatory synaptic transmission were completely blocked. This suggests that the residual calcium influx through LVA channels into the presynaptic terminal does not suffice to trigger transmitter release. A saturating concentration of omega-conotoxin GVIA (omega-CgTx) (2.5 microM) blocked one-third of whole-cell HVA calcium currents and evoked EPSCs. The dihydropyridine nifedipine (50 microM) reversibly reduced whole-cell HVA calcium currents in a voltage-dependent manner but not excitatory synaptic transmission. Cd and omega-CgTx did not alter amplitude distributions of miniature EPSCs, demonstrating that the inhibition of synaptic transmission was due to block of presynaptic calcium channels. We conclude that excitatory glutamatergic transmission in thalamic neurons in vitro was mediated mainly by HVA calcium currents, which were insensitive to omega-CgTx and nifedipine.

Animals↗

PubMed1991

A subpopulation of bone marrow-derived macrophage-like cells shares a unique ion channel pattern with microglia.

Rat microglia share a number of antigenic, functional, and morphological similarities with macrophages from other tissues, but are characterized by a distinctly different pattern of ion channels in the cellular membrane (Kettenmann et al., J Neurosci Res 26:278-287, 1990). Macrophages typically express outward and inward K+ currents. In contrast, microglia lack outward currents and only show inwardly rectifying K+ currents, regardless of the isolation or cultivation method employed for microglia. In this study we demonstrate that a subpopulation of bone marrow-derived macrophage-like cells possesses inward rectifier K+ currents, but no outward currents and thus with regard to the electrophysiological characteristics closely resembles microglia. A second population of bone marrow-derived macrophage-like cells shows the usual channel pattern described for other body macrophages. Our results strengthen the hypothesis that in the bone marrow distinct pools of precursor cells exist, possibly reflecting an early differential lineage determination for body and brain macrophages, i.e., microglia.

Animals↗

PubMed1991

Distribution of Ca2+ and Na+ conductances during neuronal differentiation of chick DRG precursor cells.

The distribution of Ca2+ and Na+ conductances on neuronal precursor cells was investigated during differentiation. Ionic conductances on the soma or on the growth cone were isolated by superfusing all other parts of the cells with sucrose. Conductances on the neuritic shaft were detected as additional conductances after removing sucrose from the neuritis shaft. Neuronal precursor cells were isolated from chick dorsal root ganglia by selectively killing differentiated neurons. Cultured precursor cells differentiated into morphological and functional mature neurons. Functionally undifferentiated precursor cells (during the first 10 hr in culture) expressed only low-voltage-activated (LVA) Ca2+ currents. High-voltage-activated (HVA) Ca2+ and Na+ currents appeared delayed after more than 10 hr in culture. Voltage-dependent conductances, if expressed by a cell, were present on all parts of the surface membrane at all stages of differentiation. LVA Ca2+ conductances were well represented on the growth cone as well as on the soma in functionally undifferentiated precursor cells. During differentiation of precursor cells, LVA Ca2+ and HVA Ca2+ as well as Na+ conductances were expressed on the somatic membrane, on the neuritic shaft, and on the growth cone. These results demonstrate the expression of Ca2+ channels on growth cones during differentiation.

Animals↗

PubMed1990

Effects of a small bolus dose of ANF in healthy volunteers and in patients with volume retaining disorders.

Thirty-seven patients with volume-retaining disorders (liver cirrhosis with ascites, n = 8; heart failure NYHA III-IV, n = 12; endstage renal failure, n = 17) and twelve healthy age-matched controls were given a small dose (33 micrograms) of hANF (human atrial natriuretic factor). We tested the resulting hemodynamic and renal effects as well as the effect on plasma cyclic GMP levels and compared them with the properties of platelet ANF receptors. The ANF injection evoked an increase in cyclic GMP plasma levels of 19.3 +/- 2.2 nM in healthy controls. This increase tended to be smaller in the cirrhosis group (15.5 +/- 3.3 nM) and in the heart failure group (16.8 +/- 2.3 nM) than in the dialysis group (20.5 +/- 2.5 nM). The invasion rates of cyclic GMP were comparable in all groups, but the evasion rates increased more in the heart failure and endstage renal failure groups (27.9 +/- 7.7 min and 26.1 +/- 3.4 min, respectively) than in the cirrhosis and control groups (14.9 +/- 1.9 min and 14.2 +/- 1.9 min, respectively). Patients with endstage renal failure and congestive heart failure showed a smaller decrease in diastolic blood pressure than controls and patients with liver cirrhosis. Renal actions of ANF were diminished in cirrhosis and heart failure patients. Binding capacities of platelet ANF receptors were higher in the control group (12.2 +/- 1.5 receptors/cell) than in the patient groups (cirrhosis, 7.8 +/- 1.2; endstage renal failure, 8.0 +/- 0.9; heart insufficiency, 8.0 +/- 1.0 receptors/cell), with no differences among the patient groups. Binding affinities were not significantly different. Correlation analysis showed that the relationship between the actions of ANF and the increases in plasma cyclic GMP levels is loose and cannot predict the hemodynamic or renal effects of exogenous ANF in a given patient. Although the behavior of plasma cyclic GMP levels fails to predict the responsiveness of the body to ANF in a given patient, it does reflect the differences between the patient groups and the control group. In contrast, we found no correlation between the properties of platelet ANF receptors and ANF action.

Adult↗

PubMed1990

Low- and high-voltage-activated Ca2+ conductances in electrically excitable growth cones of chick dorsal root ganglion neurons.

Growth cone Ca2+ currents of chick dorsal root ganglion (DRG) neurons were recorded by a patch pipette located on the cell soma. Somatic and neuritic conductances were selectively blocked either with TTX and Cd2+ or by superfusing with isotonic sucrose using a laminar flow perfusion system. DRG growth cones were electrically excitable and growth cone Ca2+ currents were similar to Ca2+ currents described in DRG somata. In particular low-voltage-activated (LVA) Ca2+ conductances were well represented contrary to previous suggestions in other cell types.

Animals↗

PubMed1990

Cultured microglial cells have a distinct pattern of membrane channels different from peritoneal macrophages.

Microglia are the source of the resident macrophages of the brain and thus belong to one of the most reactive cell types in cerebral tissue. They are attributed to have an important role in a number of pathological conditions, such as multiple sclerosis, viral infections like AIDS, and in lethal or sublethal injuries of neurons where the blood-brain barrier is left intact (Streit et al., 1988; McGeer et al., 1988; Gendelman et al., 1989). Microglia share a number of macrophage characteristics but so far lack a distinguishing positive marker. In this study it is shown that microglia are distinguished from other macrophages by a unique pattern of ion channels. We compared membrane currents of microglial cells with those from peritoneal macrophages cultured under identical conditions. Although in macrophages a delayed outward K+ current was previously described (Randriamampita and Trautmann, 1987), microglial cells lacked any specific outward current. Instead, these cells were characterized by large inwardly rectifying currents, activated by hyperpolarizing voltage steps. The reversal potential in different K+ gradients and the sensitivity of the current to to Ba2+, TEA, and 4-AP indicates that this current is K+ selective. In single-channel recordings, a 30 pS K+ selective channel similar to the classical inward rectifier K+ channel was observed. Thus, the expression of membrane channels served not only to distinguish microglia from other cells inside and outside the brain, e.g., blood macrophages, but also suggests a unique functional state of this cell population.

Animals↗

PubMed1989

Proton-induced Na+ current develops prior to voltage-dependent Na+ and Ca2+ currents in neuronal precursor cells from chick dorsal root ganglion.

Proton-induced Na+ currents (INa(H] were measured in precursor cells from chick dorsal root ganglia with whole-cell patch-clamp recording. Precursor cells were isolated using the method of Rohrer et al. (EMBO. J., 4 (1985) 1709-1714) and fast pH changes were applied with a technique developed by Davies et al. (J. Physiol. (Lond.), 400 (1988) 159-187). Proton-induced transient Na+ currents showing the same properties as in more mature neurons could be elicited already early in differentiation, before high-voltage activated Ca2+ currents and voltage-dependent Na+ currents develop.

Animals↗

PubMed1989

Proton-induced chloride current and voltage-activated Na+ and Ca2+ currents in embryonic neurons from the medicinal leech (Hirudo medicinalis).

Voltage-activated ionic currents and currents induced by step changes in proton concentration (pH 7.9-6.7) were studied in early embryonic neurons from Hirudo medicinalis. Ganglia were dissociated at embryonic day (E) 8-15, and the largest neurons were investigated using whole-cell patch clamp recording. All cells studied displayed voltage-activated Na+ and Ca2+ currents. Step changes in pH induced sustained currents which reversed at the equilibrium potential for Cl- and were blocked by substituting Cl- with acetate or sulfate. These currents thus differ in their ion selectivity from proton-induced currents in vertebrate neurons which are carried by Na+.

Animals↗

PubMed1989

Effects of a bolus dose of atrial natriuretic factor in young and elderly volunteers.

We assessed the haemodynamic and renal effects as well as the effects on plasma cGMP levels of a small i.v. dose (33 micrograms) of human atrial natriuretic factor (99-126; hANF) in two age groups of healthy volunteers. Binding properties of platelet ANF receptors were also measured. The elderly (four males, eight females, mean age 52.3 years) showed increased haemodynamic (decrease in blood pressure) and renal responses (diuresis, natriuresis, calciuresis) as well as greater increases in plasma cGMP levels and urinary cGMP excretion than the young subjects (four males, 12 females, mean age 26 years). Binding capacities and affinities of platelet ANF receptors were identical in both groups. These data indicate that the sensitivity to ANF increases with age and that this increased sensitivity is reflected in the reactivity of plasma cGMP levels but not in the properties of platelet ANF receptors. The data may be important for the therapeutic use of ANF, for the understanding of the physiological regulation of ANF action and may underline the necessity of using age-matched control subjects for clinical studies on the possible therapeutic effectiveness of ANF.

Adult↗

PubMed1988

Development of dopamine-containing neurons and dopamine uptake in embryos of Hirudo medicinalis.

The embryonic development of neurons which contain or take up dopamine was studied with glyoxylic acid histofluorescence in Hirudo medicinalis. Beginning at the time of the formation of the tail ganglion, one pair of dopamine-containing neurons was stained per segmental ganglion. The normal outgrowth of the cell bodies into the anterior roots was prevented in isolated and cultured chains of embryonic ganglia. Preincubation of intact embryos in dopamine led to the staining of additional neurons at certain developmental stages. These neurons presumably are the precursors of serotonin-containing cells, which have a temporary capability of taking up and storing dopamine.

Animals↗

PubMed1988

Is cyclic GMP a clinically useful marker for ANF action?

The action of ANF is, at least in part, mediated by the activation of particulate guanylate cyclase. Increases in plasma ANF levels induce a marked increase in the plasma levels and urinary excretion of cyclic GMP. In contrast to agents that stimulate particulate guanylate cyclase, activators of soluble guanylate cyclase, such as the bioactive molsidomine metabolite, SIN 1, induce only a modest, not significant, increase in plasma cyclic GMP levels. Thus, increases in plasma cyclic GMP levels appear to be specific for the activation of particulate guanylate cyclase. Cyclic GMP is stable in whole blood in the presence of EDTA and can easily be measured in plasma and urine. It may therefore be a valuable alternative for ANF measurement in the clinical routine. In contrast to urinary ANF excretion, the urinary excretion of cyclic GMP sensitively reflects increases in plasma ANF levels. Measurement of cyclic GMP excretion may therefore be an alternative for plasma ANF and plasma cyclic GMP measurement especially in situations where blood drawing is difficult, e.g. in newborns. Measurement of basal cyclic GMP followed by determination of increases in cyclic GMP levels after injection of a small ANF bolus dose tests the cellular sensitivity to ANF. This may give further insight in the mechanism of the regulation of ANF effects. Therefore, cyclic GMP in many cases appears to be a sensitive marker for the action of ANF in man.

Atrial Natriuretic Factor↗

PubMed1988

Development of inward currents in chick sensory and autonomic neuronal precursor cells in culture.

The development of ionic inward currents was studied in cultured neuronal precursors from chick sensory dorsal root ganglia (DRG) and compared with neuronal precursors from the cholinergic ciliary ganglia (CG) using whole cell patch-clamp recording. Neuronal precursors devoid of neuron-specific surface markers were isolated during the period of neuronal birth, i.e., at embryonic day (E) 6 from DRG and at E4.5 from CG. All neuronal precursor cells from DRG, as well as CG, showed outward K+ currents directly after they had attached to the substrate. During the first 5 hr in culture, half of the DRG cells had no inward currents at all, whereas the other half displayed a rapidly and fully inactivating Ca2+ current, which was activated with small depolarizing pulses from a holding potential of -80 mV to a -50 mV membrane potential (low-voltage-activated current, LVA). At these early stages, no other inward currents were resolved. TTX-blockable Na+ currents and slowly inactivating classical Ca2+ currents, which were activated with larger depolarizing pulses to a -20 mV membrane potential (high-voltage-activated currents, HVA) appeared concurrently after 15-20 hr in culture. In contrast, more than half of the CG cells showed LVA currents, as well as Na+ currents, as early as during the first 5 hr in culture. The HVA Ca2+ currents from the majority of the cells could be recorded only after 10-15 hr in culture. In both types of precursor-derived neurons, the LVA Ca2+ current preceded the classical HVA Ca2+ current. However, the temporal relation of the first Na+ currents to the first HVA Ca2+ currents seemed to be different in the 2 preparations. In DRG cells, Na+ and HVA Ca2+ currents appeared at the same time, whereas in CG cells, the HVA Ca2+ current showed a time lag with respect to the Na+ current. In addition, the relative amplitudes of the currents differed in the CG and DRG cells. This shows that as early as E4-6, shortly after their terminal mitosis, neurons from distinct peripheral ganglia in chick vary in the development of their basic ionic currents.

Animals↗

PubMed1986

In situ measurements of external pH and optical density oscillations in Dictyostelium discoideum aggregates.

In situ measurements of extracellular pH by means of microelectrodes and in situ measurements of optical density were performed on aggregating cells of Dictyostelium discoideum. Early aggregation stage AX2 cells showed sinusoidal pH oscillations, which could be inhibited by the specific relay inhibitor caffeine, indicating that they were coupled to cAMP oscillations. Sometimes biphasic pH oscillations were found, which can be explained by the superposition of two harmonic pH oscillations. These harmonic oscillations might arise by gating of the cAMP signal; a part of the cells respond to every cAMP signal and another subpopulation to every second cAMP pulse. Late aggregation-stage cells showed complex changes of the extracellular pH, which could be inhibited by caffeine. Optical density measurements of wave propagation in aggregation streams of HG220 also revealed gating behavior. In addition to sinusoidal optical density oscillations, biphasic and still more complex oscillations were observed.

Cell Aggregation↗