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E Heilbronn

Publications and source records attributed to E Heilbronn.

At least 19 recordsLinked to original sources
PubMed1995

Ligand-binding properties of an unusual nicotinic acetylcholine receptor subtype on isolated outer hair cells from guinea pig cochlea.

Acetylcholine receptors on isolated guinea pig cochlear outer hair cells (OHC) were characterized by radioligand binding. Equilibrium binding of [125I]alpha-bungarotoxin revealed a KD of 62 +/- 2 nM, Bmax = 7.2 +/- 1.8 x 10(7) binding sites/OHC, and a slowly reversible dissociation rate constant, kappa-1 = 2.2 +/- 0.01 x 10(-4) min-1. L-[3H]Nicotine bound reversibly (estimated KD approximately 230 nM and Bmax approximately 5 x 10(7)) with kinetic rate constants of association kappa-1 = 6.2 +/- 0.06 x 10(4) min-1 nM-1 and dissociation kappa-1 = 0.23 +/- 0.003 min-1. [3H]Strychnine bound to OHC with a KD of 35 +/- 6 nM and Bmax = 2.6 +/- 0.5 x 10(7), and binding increased 3-4 fold after membrane depolarization with 56.2 mM [K+], suggesting additional binding sites. Binding, seen only at > nM concentrations, of [3H]3-quinuclidinyl benzilate (KD = 11.5 +/- 5 nM; Bmax = 2.5 +/- 0.6 x 10(6)) was competitively inhibited by the muscarinic antagonists atropine and 4-DAMP (IC50 of 6.1 +/- 0.5 and 6.5 +/- 0.4 nM). The OHC receptor is thus an atypical nicotinic acetylcholine receptor subtype with unusual pharmacological properties.

Animals↗
PubMed1992

Tetrahydroaminoacridine and related compounds interfere with fura-2 and indo-1.

In earlier experiments, using a fluorimetric method (fura-2), we found what seemed to be a decreased cytoplasmic [Ca2+] in neuroblastoma cells when 1,2,3,4-tetrahydro-9-aminoacridine (THA) was added, but discovered by repeating our work under cell-free conditions, that THA affected the Ca(2+)-fura-2 signal. The present study aimed at investigating the previously observed interference of THA with fura-2. 1 mM THA completely inhibits fluorescence of fura-2 and another Ca(2+)-indicator, indo-1, 1 microM each (apparent IC50 = 40 microM), presumably by absorbing excitation light.

4-Aminopyridine↗
PubMed1992

Receptor alterations in manganese intoxicated monkeys.

The density of four different receptors and one marker of dopamine uptake sites were analyzed in monkey brains after manganese exposure (0.1 g manganese per month during 26 months, a dose comparable to that workers might inhale in dusty environments) by means of quantitative receptor autoradiography. The binding of 3H-mazindol to the dopamine uptake sites was reduced by 75% in both the head of the caudate nucleus and putamen, while it remained unchanged in the other regions analyzed. The binding of the D1 receptor ligand 3H-SCH 23,390 was reduced about 45% in the same areas as mazindol binding, while the density of D2 receptors was unaffected. The muscarinic acetylcholine receptors as well as GABAA receptors remained also unchanged in all brain areas analyzed after manganese exposure. Thus the dopaminergic neurons must be considered to be vulnerable to manganese concentrations attainable in the work environment. Our results also indicate that postsynaptic structures containing D1 receptors are sensitive while cells containing D2 receptors are either spared or compensated for by up-regulation of the number of receptors on remaining sites.

Animals↗
PubMed1992

Manganese induced brain lesions in Macaca fascicularis as revealed by positron emission tomography and magnetic resonance imaging.

A series of positron emission tomography scans was made on two monkeys during a 16-month period when they received manganese(IV)oxide by subcutaneous injection. The distribution of [11C]-nomifensine uptake, indicating dopamine terminals, was followed in both monkey brains. The brain distributions of [11C]-raclopride, demonstrating D2 dopamine receptors, and [11C]-L-dopa, as a marker of dopamine turnover, were followed in one monkey each. The monkeys developed signs of poisoning namely unsteady gait and hypoactivity. The [11C]-nomifensine uptake in the striatum was reduced with time and reached a 60% reduction after 16 months exposure. This supports the suggestion that dopaminergic nerve endings degenerate during manganese intoxication. The [11C]-L-dopa decarboxylation was not significantly altered indicating a sparing of [11C]-L-dopa decarboxylation during manganese poisoning. A transient decrease of [11C]-raclopride binding occurred but at the end of the study D2-receptor binding had returned to starting values. The magnetic resonance imaging (MRI) revealed that the manganese accumulated in the globus pallidus, putamen and caudate nucleus. There were also suggestions of gliosis/edema in the posterior limb of the internal capsule. MRI might be useful to follow manganese intoxication in humans as long as the scan is made within a few months of exposure to manganese, i.e. before a reversal of the manganese accumulation.

Animals↗
PubMed1991

A nicotinic acetylcholine receptor-like alpha-bungarotoxin-binding site on outer hair cells.

Acetylcholine (ACh) appears to be the major neurotransmitter liberated from olivocochlear efferents terminating on outer hair cells (OHC). Recently, cholinergic receptor epitopes were visualized at the basal pole of the OHCs. To evaluate the ACh receptor type at OHC we performed binding studies with [125I]-labelled alpha-bungarotoxin (alpha-bgtx), a close to irreversibly acting blocker of the nicotinic acetylcholine receptor (nAChR) of skeletal muscle and of electrocytes of Torpedo and Electrophorus. An irreversible and saturable binding (80 nM) of the radiolabelled compound to OHCs was observed. The number of alpha-bgtx sensitive binding sites present on each OHC was calculated to be about 2 X 10(-17) mol/OHC, which would amount to about 10(7) binding sites/cell. Preincubation with the reversibly acting cholinergic ligands, carbamylcholine (1 mM), nicotine (0.1 mM) and d-tubocurarine (1-100 microM) was found to inhibit alpha-bgtx binding to a varying degree. Atropine (0.05 mM), a muscarinic antagonist, had no influence on the binding of alpha-bgtx to OHCs. [3H]-QNB, a specific marker and antagonist for muscarinic AChR, and [125I]-kappa-toxin, known to react with neuronal and ganglionic nAChR, showed no specific binding to OHCs. The data indicate that a peripheral type nAChR is present on OHCs mediating ACh-induced modulation of the biomechanics of the cochlea by influencing OHC motility.

Animals↗
PubMed1990

Receptor-triggered polyphosphoinositide turnover produces less cytosolic free calcium in cultured dysgenic myotubes than in normal myotubes.

Myotubes prepared from mice with muscular dysgenesis (mdg) were used to further elucidate the putative role of inositol triphosphate (InsP3) in excitation-contraction (E-C) coupling of skeletal muscle. The mdg mutation is characterized by an uncoupling of the E-C coupling. InsP3 production in normal and mdg/mdg myotube cultures and its relation to the levels of cytosolic free calcium were analyzed. Basal and ATP-stimulated levels of InsP3 were equal in normal and mdg/mdg myotube cultures. In contrast, the transient increases of cytosolic free calcium in mdg/mdg myotubes in culture were generally much lower than those in normal ones. This suggests that the defect in dysgenic myotubes does not rest on the InsP3 formation but on the InsP3-triggered transduction of excitation and/or the induction of calcium release from internal stores.

Adenosine Triphosphate↗
PubMed1989

Extracellularly applied ATP alters the calcium flux through dihydropyridine-sensitive channels in cultured chick myotubes.

Extracellularly applied ATP mediates a biphasic calcium signal in cultured chick myotubes. A rapid and transient increase in cytosolic calcium was independent of extracellular calcium while a second signal, slower in onset and decay, was absent without extracellular calcium. In depolarized myotubes, the cytosolic [Ca2+] was increased more than ten times above baseline level. Addition of ATP to the incubation medium immediately increased the rate of return of cytosolic Ca2+ levels to baseline. The ATP effect was half-maximal at about 10 microM ATP and was mimicked by ATP S. This ATP-sensitive calcium influx was also rapidly stopped by addition of dihydropyridines such as PN 200-110, suggesting that it is the voltage operated Ca2+-channel that was inactivated by ATP.

Adenosine Triphosphate↗
PubMed1989

Action potentials of cultured human oat cells: whole-cell measurements with the patch-clamp technique.

Oat cells (of the small cell carcinoma of the lung) have been reported to generate calcium action potentials. The calcium channels have further been suggested to play a crucial role in the relation between oat cell carcinoma and the often associated myasthenic syndrome. We have examined cultured human oat cells (U-1690) under voltage-clamp conditions, using the patch-clamp technique. We found, contrary to previous reports, that the action potential was caused by sodium and potassium currents. No calcium current was detected under these conditions, which indicates that calcium channels, if present, are very rare. The findings restrict, but do not rule out, the hypothesis that calcium plays a key role in the carcinoma/myasthenic syndrome relation.

Action Potentials↗
PubMed1988

P2-purinoceptor-stimulated phosphoinositide turnover in chick myotubes. Calcium mobilization and the role of guanyl nucleotide-binding proteins.

ATP, a trigger of P2-purinoceptor-mediated polyphosphoinositide (PI) turnover in cultured myotubes, increased cytosolic calcium levels in a time- and dose-dependent manner (quin2 fluorescence). The calcium was released from intracellular stores, as acute addition of 5 mM EGTA was without significant effect. Adenosine 5'-(3-thiotriphosphate) and 5'-adenylyl imidodiphosphate also increased intracellular levels of inositol phosphates (InsP) and cytosolic calcium levels. Treatment with cholera or pertussis toxin of myotube cultures did not affect the P2-purinoceptor-mediated InsP increase although PI turnover in permeabilized myotubes was stimulated by guanosine 5'-(3-thiotriphosphate). The results suggest that myotube P2-purinoceptors trigger PI turnover and increase intracellular free calcium levels, via a mechanism insensitive to ADP-ribosylation, by cholera or pertussis toxin of guanyl nucleotide-binding (G) proteins. However, the presence of a phospholipase C-coupled G-protein was otherwise demonstrated.

Adenosine Triphosphate↗
PubMed1987

Externally applied adenosine-5'-triphosphate causes inositol triphosphate accumulation in cultured chick myotubes.

In striated muscle, adenosine-5'-triphosphate (ATP) potentiates the responses to acetylcholine. The underlying biochemical events are unknown. Here we report that ATP, externally applied to chick myotubes, induces a rapid, dose-dependent accumulation of intracellular inositol triphosphate which is correlated with a decrease in phosphatidyl 4,5-bisphosphate. Adenosine-5'-diphosphate, adenosine-5'-monophosphate and adenosine are less potent while beta, gamma-imido ATP is equipotent motoneurons and/or skeletal muscle controls the activation of a polyphosphoinositide phosphodiesterase via a cell membrane P2-purinoceptor, thus modulating skeletal muscle responses to transmitter release.

Acetylcholine↗
PubMed1987

Forskolin blocks carbachol-mediated ion-permeability of chick myotube nicotinic receptors and inhibits binding of 3H-phencyclidine to Torpedo microsac nicotinic receptors.

Forskolin, a commonly used adenylate cyclase activator, was found to inhibit reversibly the carbachol-induced ion-translocating capacity of the nicotinic acetylcholine receptor (nAChR) on chick myotubes in a dose- (IC50 = 20 microM) and time-dependent manner. This effect was not correlated to increases in cellular cAMP. Forskolin, at a concentration (50 microM) that totally blocked the carbachol-induced 86Rb influx, caused no change in carbachol or alpha-bungarotoxin binding to chick myotube nAChR in situ. In contrast, in the presence of carbachol, forskolin inhibited (IC50 = 10 microM) the binding of 3H-phencyclidine, a putative nAChR ion-channel ligand, to Torpedo microsac nAChR. Inhibition of 3H-phencyclidine binding in the absence of carbachol was not complete. Membrane leakage studies on myotubes, measuring 3H-efflux from 2-deoxy-D(1-3H)-glucose loaded cells and electrophysiological measurements of membrane properties supported the interpretation that forskolin induced decreases in plasma membrane permeability. In conclusion, forskolin blocks the carbachol-mediated increase in permeability of the nAChR channel by (1) binding to the ion-channel (open state) and (2) generally perturbing the plasma membrane function possibly by interfering with the protein-lipid interface.

Animals↗
PubMed1987

Effect of long-term administration of manganese on biogenic amine levels in discrete striatal regions of rat brain.

The effect of long-term manganese exposure of rats on biogenic amine levels in striatal brain regions is described. Four groups of male Sprague-Dawley rats received manganese as MnCl2 continuously in the drinking water for 60, 100, 165 and 265 days, respectively. Discrete regions within the caudate-putamen were punched out. Dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, serotonin and 5-hydroxyindoleacetic acid were determined by high performance liquid chromatography with electrochemical detection. Rats exposed for 60 and 165 days showed significantly increased levels of dopamine and 3,4-dihydroxyphenylacetic acid in discrete regions of the dorsal caudate-putamen. The affected regions were possibly not identical in the two age groups but they were adjacently situated. These alterations were not found in rats exposed for 100 or 265 days.

Animals↗
PubMed1987

Effects of manganese oxide on monkeys as revealed by a combined neurochemical, histological and neurophysiological evaluation.

Four monkeys were exposed to a total of 8 g each of manganese as oxide by repetitive subcutaneous injections during 5 months, after which they were left for 1 week to 6 months before they were sacrificed. All animals developed hyperactive behaviour after about 2 months. About 5 months after the start of the exposure the animals became hypoactive with an unsteady gait, and subsequently an action tremor appeared in some of the animals. The animals lost power in both upper and lower limbs and the movements of the hands and feet were very clumsy. The serum content of manganese rose 10-40 times during the exposure time and the content in brain was generally increased more than 10 times, with the highest content found in globus pallidus and putamen. The observed neurochemical effects were also largest in globus pallidus and putamen. In these regions there was a considerable depletion of dopamine and 3,4-dihydroxyphenylacetic acid, while the homovanillic acid content remained almost unchanged. A severe neuronal cell loss was observed in globus pallidus but not in other regions. This is in accordance with results from the most recent neuropathological study of a human suffering from chronic manganese poisoning [Yamada et al. (1986) Acta Neuropathol 70: 273-278] where globus pallidus was devoid of neuronal cells while the content of pigmented cells in substantia nigra was normal. Our data suggest a reduction in number of dopaminergic nerve terminals, as the activity of the dopamine synthesizing enzyme DOPA-decarboxylase was also lowered.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Some biochemical characteristics and cell membrane actions of a toxic phospholipase A2 isolated from the venom of the pit viper Agkistrodon halys (Pallas).

A toxic component (AgTx) from the venom of Agkistrodon halys (Pallas) was isolated using DEAE-cellulose DE11 and CM-Sephadex C50 column chromatography and finally purified to homogeneity by FPLC on a MonoQ column. The toxin is a neutral (pI 6.9) single chain polypeptide with a mol. wt of 14,000 and an amino acid composition (123 residues) roughly similar to that of notexin. AgTx was found to have phospholipase A2 activity which was dependent on calcium and stimulated by sodium deoxycholate. The toxin caused efflux of 2-deoxy-(1-3H)-glucose-6-phosphate (a cell membrane integrity probe) as well as of [3H]acetylcholine from rat brain synaptosomes. No cell membrane damage was induced by AgTx on cultured N1E 115 neuroblastoma cells and chick myotube cultures. The LD50 ws 150 micrograms/kg (i.p.) in mice. The main symptom observed was respiratory paralysis. The results obtained show that AgTx can be classified as a toxic phospholipase A2 with a presynaptic site of action.

Acetylcholine↗
PubMed1987

Isolation and pharmacological characterization of a new alpha-neurotoxin (alpha-AgTx) from venom of the viper Agkistrodon halys (Pallas).

A hitherto unknown alpha-neurotoxin, alpha-agkistrodotoxin, was isolated from the venom of the pit viper Agkistrodon halys (Pallas). It's molecular weight was approx. 8000 +/- 80 (SDS-polyacrylamide electrophoresis). The toxin crossreacted with antiserum directed against alpha-bungarotoxin and inhibited binding of 125I-alpha-bungarotoxin to the nicotinic acetylcholine receptor of cultured myotubes (IC50 = 2 X 10(-9) M). The association and dissociation rates were 4.85 X 10(5) per mole per min and 3.55 X 10(-4) per min, respectively, giving a Kd of 7.3 X 10(-10) M. The toxin also inhibited carbachol-induced influx of cations through the nAChR (IC50 = 6 X 10(-8) M).

Animals↗