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Biomedical subjects

E Habermann

Publications and source records attributed to E Habermann.

At least 73 records · Page 4Linked to original sources
PubMed1984

Novel 1,4-dihydropyridine (Bay K 8644) facilitates calcium-dependent [3H]noradrenaline release from PC 12 cells.

The effects of the novel 1,4-dihydropyridine Bay K 8644 [methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)-pyridine- 5-carboxylate] on the release of [3H]noradrenaline in cultured PC 12 cells were investigated. K+ in a concentration-dependent manner evoked 3H-transmitter release with an EC50 of 50-56 mM. Bay K 8644 at 30 nM potentiated the K+-evoked [3H]noradrenaline release; however, in the absence of calcium neither K+ evoked nor Bay K 8644 enhanced [3H]noradrenaline release. At a K+ concentration of 25 mM, Bay K 8644 stimulated [3H]noradrenaline release fivefold, with an EC50 of 10 nM, and 100 nM of the calcium channel blocker nitrendipine shifted the concentration response curve of Bay K 8644 to the right in an apparently competitive fashion. Nitrendipine blocked the Bay K 8644-potentiated release with an EC50 of 700 nM in the presence of 500 nM Bay K 8644. [3H]Nitrendipine bound to a saturable population of binding sites on PC 12 cell membranes with a Bmax of 180 fmol X mg-1 of membrane protein and a KD of 0.9 nM. Bay K 8644 inhibited [3H]nitrendipine binding with a Ki of 16 nM. It is concluded that Bay K 8644 binds to, and stabilizes, the open state of calcium channels and thus acts as a "calcium agonist" to mediate calcium-dependent cellular events such as catecholamine release from PC 12 cells.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1984

Quantitative autoradiography of [125I] apamin binding sites in the central nervous system.

The binding sites for [125I] apamin in the central nervous system of rat, guinea-pig, chicken and frog were assessed by quantitative autoradiography on X-ray film. In rat and guinea-pig brain apamin labels preferentially the limbic-olfactory system, i.e. nucleus olfactorius, nuclei septi, habenula and hippocampus. In the rat spinal cord the peptide binds preferentially to the substantia gelatinosa. Tectum opticum and nuclei isthmi are labelled in chicken brain. In frog brain no preferentially "apamin-stained" area was found. The role of the cerebral binding sites is still unknown, whereas the spinal sites may be involved in apamin poisoning.

Animals↗
PubMed1983

Intrathecal apamin selectively facilitates activity in ascending axons of rat spinal cord evoked by stimulation of afferent C fibers in sural nerve.

Intrathecally administered apamin was tested for its effect on activity in ascending axons of the spinal cord using decerebrate rats with low spinal cord transection. Afferent A beta, A delta or C fibers were stimulated in the sural nerve, and the response evoked in ascending axons was recorded below the transection. Apamin (5 ng) produced an increase in C fiber-evoked activity which developed about 30 min after injection and persisted for more than 60 min after injection. Apamin (5, 20 and 50 ng) did not change the activity in ascending axons which responded only to stimulation of afferent A beta and A delta fibers. The results indicate that apamin facilitates synaptic transmission from high-threshold afferent C fibers to secondary neurons.

Afferent Pathways↗
PubMed1983

Lead and other metals can substitute for Ca2+ in calmodulin.

We have studied the interaction between some heavy metal ions, as compared with earth alkali ions, and calmodulin, a tissue protein which binds Ca2+ and mediates some of its effects. 1. Calmodulin dependent phosphodiesterase was activated with Pb2+, Ca2+, Sr2+, Ba2+, and Cd2+ (EC50 about 0.8 microM). The maximal activation achieved decreases in the order given. Hg2+, Sn2+, Fe2+, Cu2+, Ni2+, Bi3+, and Sb3+ up to 20 microM did not activate. 2. Pb2+ can replace Ca2+ with respect to the calmodulin-dependent phosphorylation of brain membranes. With high Pb2+ concentrations, phosphorylation was inhibited. 3. Calmodulin binding to brain membranes was enhanced with concentrations below 10(-4)M in the following order: Pb2+ greater than or equal to Ca2+ approximately Sr2+ greater than Cd2+ greater than Mn2+ greater than Ba2+. In contrast Mg2+, Hg2+, Sn2+, Fe2+, Ni2+, Co2+, and Cu2+ triggered, if at all, a non-saturable binding of calmodulin. 4. In the flow-dialysis, other ions competed with 45Ca2+ binding to calmodulin in the following order: Pb2+ approximately Ca2+ greater than Mn2+, Ba2+, Cd2+, Sr2+. Thus among the ions investigated Pb2+ is a fully potent substitute for Ca2+ in every calmodulin-dependent reaction investigated. Cd2+ is always much less potent. The earth alkali ions Sr2+ and Ba2+ take an intermediate position. It remains to be shown whether calmodulin is merely a storage site for Pb2+, or whether the resulting functional changes play a role in Pb2+ poisoning.

Animals↗
PubMed1983

Action and binding of palytoxin, as studied with brain membranes.

Palytoxin in concentrations as low as 10(-11) to 10(-12) M promotes the outflow of the lipophilic [3H]tetraphenylphosphonium ion from particulate brain cortex of guinea-pigs and rats, and from preloaded crude synaptosomes of rats, which indicates depolarization. The outflow is not influenced by tetrodotoxin or the calcium channel blocker nimodipin, or by substitution of choline for Na+ ions. It is increased by Ca2+ and by borate, the latter interacting with the toxin itself. To assess the fixation of palytoxin to biological membranes, a binding step was installed before the depolarization step. Palytoxin binds to membranes from rat brain, liver, kidney, human and dog erythrocytes, and to a lesser degree to liposomes made from rat brain or erythrocyte lipids. Binding is reversible. It is decreased by mild physical pretreatments of crude synaptosomes. Palytoxin binding is increased in the presence of micromolar concentrations of Ca2+ or borate. It is concluded that the potentiation of palytoxin actions by Ca2+ or borate is at least partially due to the promotion of its binding.

Acrylamides↗
PubMed1983

Monoclonal antibodies against tetanus toxin and toxoid.

Monoclonal antibodies against tetanus toxin and its toxoid were produced by immunizing mice with toxoid or toxin. They were measured by an enzyme-linked immunosorbent assay (ELISA), by a toxin neutralization test in mice (in vivo prevention test), and by their ability to prevent binding of 125I-toxin to brain membranes or gangliosides (in vitro prevention test). Six monoclonal antibodies obtained by immunization with toxoid (anti-toxoid 1-6) were investigated in more detail. They belonged to IgG class 1. Three of them (anti-toxoid 1, 2 and 3) recognized both toxoid and toxin as well as fragment B and the light chain of toxin, but not fragment C. Two other antibodies (anti-toxoid 4 and 5) were directed against toxoid only. Neither of them prevented toxin action in vitro or in vivo. Anti-toxoid 6 recognized toxin, toxoid and fragment C, but not light chain, and prevented toxin action in vitro and in vivo. Immunization against toxin was initiated with a toxin-antitoxin complex and boosted with toxin. We studied six antibodies in more detail, all of IgG type 2. Their KD against 125I-tetanus toxin varied from 10(-9) to 10(-10) M. Anti-toxin 2 recognized toxin, toxoid, light chain and fragment B, but not fragment C. The others reacted with toxin, toxoid and fragment C, but not with light chain or fragment B. All of them prevented toxin action in vitro and in vivo. As calculated from the maximal extinction achieved in the ELISA, tetanus toxin combined with a maximum of two different antibody molecules from our set. Gel filtration data indicate that tetanus toxin reacts with monoclonal antibodies one by one. Compared with polyclonal antiserum, monoclonal antibodies yield flatter slopes in both in vitro and in vivo prevention tests. Thus, they cannot substitute for the polyclonal antibodies in clinical situations, and cannot be calibrated in international units.

Animals↗
PubMed1983

Tetanus toxin inhibits the evoked outflow of an inhibitory (GABA) and an excitatory (D-aspartate) amino acid from particulate brain cortex.

In order to elucidate the mode of action of tetanus toxin, particles from rat forebrain were preloaded with tritiated GABA or D-aspartate, pre-incubated with tetanus toxin and then depolarized with K+, either in a batch procedure or by superfusion. The toxin depresses, but does not abolish, the evoked outflow of both amino acids in either system. Omission of Ca2+ decreases the outflow in the batch procedure by about 40%. The remaining outflow of either amino acid is insensitive to tetanus toxin, whereas the Ca2+ dependent outflow is completely inhibited. Antitoxin neutralizes the toxin but does not reverse its in vitro effects, once manifest. The toxin effects increase with time and temperature of pre-incubation. Pretreatment of the particles with V. cholerae neuraminidase, which is known to convert the long-chain gangliosides quantitatively into GM1, does not decrease the sensitivity to tetanus toxin. Besides particles from rat brain, those from chicken, but not those from frog brain, are toxin-sensitive when tested for GABA outflow in the batch procedure. Frog brain does not yield the typical ganglioside pattern, and also does not measurably bind 125I-tetanus toxin. The homoexchange diffusion of GABA, but not of D-aspartate, is slightly facilitated by tetanus toxin. We confirmed that tetanus toxin slightly inhibits the uptake of GABA, whereas that of D-aspartate is not measurably influenced. The accumulation, driven by a Na+/K+ gradient, of GABA into membrane vesicles from rat cortex is not affected by tetanus toxin. The present data support the hypothesis that tetanus toxin influences a process involved in the outflow of many transmitters, both excitatory and inhibitory.

Animals↗
PubMed1983

Tetanus and botulinum toxins inhibit, and black widow spider venom stimulates the release of methionine-enkephalin-like material in vitro.

The actions of tetanus toxin, botulinum A toxin, and black widow spider venom on the release of methionine-enkephalin-like immunoreactivity have been studied; a particulate fraction prepared from rat striata was used. Depending on the duration of preincubation, tetanus toxin diminished the release evoked by veratridine (50 microM final concentration), and abolished it at final concentrations between 0.1 and 1 micrograms/ml. Botulinum A toxin was about 10 to 20 times less potent. Heating or pretreatment with antitoxin inactivated the clostridial toxins. The particulate fraction pretreated with V. cholerae neuraminidase retained its toxin sensitivity. Tetanus toxin also depressed the release due to sea anemone toxin II and high K+. Spider venom stimulated the release in a concentration-dependent manner and required the presence of Ca2+; its effects were depressed by tetanus toxin. These results support the view that both clostridial toxins and spider venom act as broad-range presynaptic neurotoxins on peptidergic transmitter systems.

Animals↗
PubMed1982

Changes in erythrocyte permeability due to palytoxin as compared to amphotericin B.

Palytoxin causes within minutes a temperature-dependent K+ loss from human and rat erythrocytes which is followed within hours by haemolysis. It decreases the osmotic resistance in a concentration-dependent manner, so that osmotic influences are negligible for K+ release but considerable in haemolysis. External K+ inhibits the haemoglobin release and Rb+ inhibits the release of K+ and haemoglobin. Ca2+ (over 20 microM) and borate (over 5 microM) enhance the loss of K+ and haemoglobin. With both Ca2+ and borate present, the efficacy of palytoxin is raised about 10 000-fold. Under these conditions, about 15 palytoxin molecules per human cell trigger a 50% K+ loss over a wide range of cell concentrations. The palytoxin effect is reversible. After depletion from K+ by low concentrations of palytoxin, human cells can be refilled with K+ and resealed. The pores formed by palytoxin are small. They allow the entrance of Na+ and choline, whereas inositol is largely excluded and Ca2+, as well as sucrose and inulin, are completely excluded. Amphotericin B resembles palytoxin in its ability to cause a considerable prelytic K+ loss and to form small pores. However, it is about 1000-times weaker than palytoxin, is not inhibited by K+ or Rb+, is not activated by Ca2+ or borate, and has a negative temperature dependence. Thus palytoxin represents a novel type of cytolysin.

Acrylamides↗
PubMed1982

Ouabain inhibits the increase due to palytoxin of cation permeability of erythrocytes.

1. Palytoxin in concentrations as low as 1 pM raises the potassium permeability of rat, human and sheep erythrocytes, and the sodium permeability of human erythrocytes. The release of potassium or sodium from human cells also occurs when extracellular sodium is replaced by choline. 2. Ouabain inhibits the release due to palytoxin of potassium ions from human, sheep and rat erythrocytes, and also the release of sodium ions from human cells. The glycoside effect is specific since a) it is already prominent with 5 X 10(-8) M ouabain b) rat erythrocytes are less sensitive than human cells to ouabain c) potassium release due to amphotericin B or the Ca2+ ionophore A 23187 is not influenced by ouabain and d) dog erythrocytes are resistant to palytoxin as well as to ouabain. 3. Palytoxin has no direct influence on the Na+, K+ - ATPase. It inhibits the binding of [3H]ouabain to erythrocyte membranes within the same concentration range as unlabelled ouabain. It partially displaces bound [3H]ouabain, and partially inhibits the inactivation of erythrocyte ATPase by the glycoside. Depletion of ATP or of external Ca2+ renders the cells less sensitive to palytoxin. Nevertheless inhibition by ouabain can be still demonstrated with human cells whose ATP stores had been largely exhausted, and also in the absence of external Ca2+. 4. Palytoxin decreases the surface tension at the air-water interface. We assume that the formation of nonspecific pores by palytoxin is linked with its surface activity. Further experiments should demonstrate whether ouabain prevents the binding of palytoxin to erythrocytes ("receptor hypothesis"), or whether an ouabain-sensitive hydrolysis of trace amounts of ATP ("metabolic hypothesis") promotes the palytoxin effect.

Acrylamides↗
PubMed1982

Palytoxin both induces and inhibits the release of histamine from rat mast cells.

Palytoxin (PTX) is a potent releaser of histamine from rat mast cells. The concentration response curve is bell-shaped with its range between 0.05 ng/ml and 5 micrograms/ml and its maximum at 50 ng/ml. The release of histamine by PTX is specific because (a) heat-inactivated (50 degrees C) mast cells are insensitive to PTX, and (b) extracellular calcium is essential. Removal of extracellular potassium as well as the presence of borate shifts the curve to the left by factor of 10. At higher concentrations (5 micrograms/ml), PTX inhibits the release of histamine due to compound 48/80, MCD-peptide, Con-A, ionophore A-23187, and PTX itself.

Acrylamides↗
PubMed1981

Delayed haemolytic action of palytoxin. General characteristics.

1. Palytoxin is a haemolysin. The erythrocytes from various species can be classified into a sensitive and a hardly sensitive group. The former contain potassium as their main inside cation and are arranged according to their sensitivity as hog greater than or equal to rat, mouse greater than rabbit greater than guinea-pig greater than man. The latter, comprising those from sheep and cattle, have sodium as their main inside cation. In addition, chicken erythrocytes are relatively insensitive. 2. Haemolysis of rat erythrocytes is preceded by a lag period of 1--2 h. With increasing temperature the haemolysis proceeds more quickly but reaches the same final range between 25 and 42 degrees C. The pH optimum in Britton-Robinson buffer supplemented with saline is between 7 and 8. Washing off palytoxin during the prelytic period reduces the haemolytic power. 3. The sensitivity of rat erythrocytes decreases with increase of osmolarity between 235 and 415 mosM. Accordingly, their osmotic resistance is lowered by palytoxin in a concentration-dependent manner. 4. With both rat and sheep erythrocytes, potassium loss by far precedes the haemolysis due to palytoxin. Potassium loss is measurable already after 1 min and increases with time. After 2 hours the quotient between the ED50 of haemolysis and that of potassium loss is around 200. Thus palytoxin is an unusually strong but slow haemolysin of the osmotic type. The extreme prelytic potassium loss and the correlation between susceptibility and potassium content of erythrocytes points towards the relevance of ionic fluxes.

Acrylamides↗
PubMed1981

Increase of cGMP and accumulation of 45Ca2+ evoked by drugs acting on sodium or potassium channels.

Cyclic guanosine monophosphate (cGMP) and 45Ca2+ accumulation were measured in mouse cerebellar slices after treatment with compounds known to affect ion channels in excitable membranes. Scorpion toxin and sea anemone toxin II raise cGMP and 45Ca2+ contents. Both toxins are known to keep the activated sodium channel open. 4-Aminopyridine and tetraethylammonium, which block potassium conductance, also increase cGMP and promote dose-dependently the 45Ca2+ accumulation. The effects of these 4 drugs but not the effects of depolarizing K+-concentrations on the accumulation of cGMP and 45Ca2+ are inhibited by tetrodotoxin. The cyclic GMP content of non-excitable cells, such as isolated hepatocytes from rat and guinea pig, is not affected in a comparable manner. We conclude that in excitable cells, sodium influx triggers an increase of intracellular free calcium and in that way a rise of cGMP. This effect is independent of the ion channel primarily affected. Conversely, the concentration of cGMP might serve as an indicator of intracellular free calcium.

4-Aminopyridine↗