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Biomedical subjects

A Hermann

Publications and source records attributed to A Hermann.

At least 91 records · Page 5Linked to original sources
PubMed1994

Intracellular action of spermine on neuronal Ca2+ and K+ currents.

Intra- and extracellular effects of the polyamine spermine on electrical activity and membrane currents of identified neurons in the abdominal ganglion of Aplysia californica were studied under current- and voltage-clamp conditions. Ionophoretic injection of spermine reduced the amplitude of action potentials and altered their time course as well as spontaneous discharge activity. Investigation of membrane currents showed that intracellular spermine suppressed the total outward current but increased the inward rectifier current. After separation of ion currents it was found that the voltage-activated, delayed K+ outward current and the Ca2+ inward current were reduced by intracellular spermine in a dose- and voltage-dependent manner. The block of the K+ current can be described by a voltage-dependent reaction, where one spermine molecule binds to one channel. The binding constant Kb, at zero voltage, and the effective valency, z delta, had values of 176/M and 0.41 for cell R-15, 223/M and 0.64 for cell L-11, and 137/M and 0.42 for cell L-3. Apparently, more than one spermine cation is needed to block one Ca2+ channel, since the coefficient n, which absorbs the molecularity and cooperativity of the reaction, had non-integral values between 1.34 and 2.22. The binding constant Kb and the effective valency z delta had values of 265/M and 0.64 for cell R-15, 82/M and 0.56 for cell L-4, and 263/M and 0.51 for cell L-6. Intracellular spermine also blocked the Ca(2+)-activated K+ current induced by ionophoretic Ca(2+)-injections, but increased the current at prolonged times after spermine injection.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1994

Polyamines block Ca(2+)-activated K+ channels in pituitary tumor cells (GH3).

The effects of the natural polyamines, putrescine, spermidine and spermine on single calcium-activated potassium channels from clonal rat pituitary tumor cells (GH3) were studied. Applied to inside-out patches, polyamines were found to reduce the current amplitude and open probability of the channels in a dose- and voltage-dependent manner, indicating that polyamines act as fast blockers which sense a fraction of the electrical field in the channel pore. The Kd for spermine was 11.2 mM for the reduction of unitary current amplitude and 0.7 mM for the reduction of the open probability. The order of effectiveness was spermine > spermidine > putrescine. From fitting beta-functions to current amplitude histograms, blocking and unblocking rates were determined as 11.4 x 10(4) sec-1 and 21.9 x 10(4) sec-1, respectively. The reduction of the channel open probability was relieved by an increase of the Ca2+ concentration of the internal solution, indicating that polyamines compete with Ca2+ at the Ca2+ sensor of the channel. Putrescine antagonized the effect of spermine on the channel current amplitude. The results suggest that polyamines at intracellular millimolar concentrations suppress ion channel activity and therefore may effect electrical discharge behavior of excitable cells.

Animals↗
PubMed1994

Parvalbumin-immunoreactive material in the kidney of Xenopus laevis.

Parvalbumin-immunoreactive material has been localized in various parts of the Xenopus kidney. Ciliated epithelia in the neck segment, the intermediate segment and in the peritoneal funnel, epithelial cells intermingled among flask cells in the connecting tubule, and cells in the proximal and distal tubules cells were labelled. Renal corpuscle and collecting duct cells did not exhibit parvalbumin immunoreactivities. Western-blot analysis of kidney homogenates indicated various isoforms of parvalbumin-immunoreactive proteins.

Animals↗
PubMed1993

Calcium-binding proteins in the inner ear of Xenopus laevis (Daudin).

Parvalbumin, S-100, calbindin-D28K and calmodulin-immunoreactive sensory hair cells were located in the inner ear of tadpoles and mature frogs of Xenopus laevis (Daudin). The relative number of immunoreactive cells varied in different compartments of the inner ear, depending on the Ca-binding protein studied.

Animals↗
PubMed1993

Sarcoplasmic calcium-binding proteins in Aplysia nerve and muscle cells.

Muscle (body wall, buccal mass, heart) and neural tissue of the marine mollusc Aplysia californica was analysed for calcium-binding proteins using transblot/45Ca overlay, Western blotting and two-dimensional polyacrylamide gel electrophoresis, and several low molecular weight calcium-binding proteins were identified. Our results that Aplysia muscle contains an abundant protein with a M(r) of approximately 20,000 with strong 45Ca(2+)-binding ability and cross-reactivity to antibodies against the sarcoplasmic calcium-binding protein isoform II (SCP II) from Amphioxus. Immunocytochemical studies revealed that isoforms of SCP are distributed in a tissue-specific manner, SCP II-like protein is exclusively present in muscle fibres closely associated with the contractile machinery, whereas the isoform I (SCP I-like protein) is exclusively present in a subset of neurons, suggesting a function in their calcium regulation. In addition, a novel 45Ca(2+)-binding protein of M(r) 43,000, pl 4.7, was found in muscle and in neurons. A third protein of M(r) 40,000, pl 4.8, cross-reacts with anti-parvalbumin and anti-calbindin D-28K antibodies.

Animals↗
PubMed1993

Endocrine-like cells and insulin-binding sites in the epineurium of Helix pomatia.

Endocrine/paracrine-like cells are described for the first time in the epineurium of the cerebro-subesophageal ganglia connectives and in the epineurium of the nervus pallialis dexter et internus of Helix pomatia. At least a population of these cells contains insulin-immunoreactive material. Immunoelectron-microscopic investigations showed that electron-dense granules exhibit insulin-like material. Insulin-binding studies revealed granular cells as putative target-cells of insulin in the epineurium.

Animals↗
PubMed1993

Photodynamic effects on the nuclear envelope of human skin fibroblasts.

Photodynamic effects on the nuclear envelope of human skin fibroblasts were investigated by confocal laser fluorescence microscopy and transmembrane resting potential measurements. The results show staining of the nuclear envelope after short incubation times with Photosan III, Photofrin II and haematoporphyrin derivative (HPD) enriched with monomers. Maximum staining was found at the centre of the nuclear envelope. The sequence of fluorescence intensity was HPD enriched with monomers > Photofrin II > Photosan III. After lethal treatment with Photosan III and tetrasulphonated aluminium chloride phthalocyanine, the nuclear transmembrane potential of the nuclear membrane decreased from -20 mV to about -10 mV with reference to the plasma membrane potential.

Biological Transport↗
PubMed1992

Sarcoplasmic calcium-binding protein-immunoreactive material in the central nervous system of the snail, Helix pomatia.

In Helix pomatia a 10 kDa sarcoplasmic calcium binding protein I (SCP I)-immunoreactive material was localized immunologically in neurons of the central nervous system, including the electrically silent serotonergic metacerebral giant neuron. Antisera against sarcoplasmic calcium binding protein II (SCP II) stained a 20 kDa protein in individual muscle cells of the epineurium. SCP- and parvalbumin (PV)-immunoreactive material were not co-localized.

Animals↗
PubMed1992

Quantification of Ile-Ser-Bradykinin degradation in human serum and ascites.

A leucine aminopeptidase (LAP) and a carboxypeptidase (CP) activity in human serum and malignant ascites degrade Ile-Ser-Bradykinin (ISB = T-Kinin) in two catalytic steps to desArg9Bradykinin. The catalytic activity in serum is always higher than in ascites. In serum the carboxypeptidase activity is higher than the LAP activity whereas in ascites the two activities are not different.

Amino Acid Sequence↗
PubMed1992

Calcium-binding proteins in chemoreceptors of Xenopus laevis.

Calcium-binding proteins were investigated immunohistochemically in chemo-receptors of the olfactory epithelium and taste buds of the clawed frog, Xenopus laevis. Calmodulin-, S-100- and calbindin-immunoreactive material were found in sensory cells of the olfactory epithelium; however, parvalbumin-like material was absent in these cells. Taste buds of the palate showed calmodulin-, S-100- and parvalbumin-immunoreactive material in sensory cells, while calbindin-immunoreactive material in supporting cells. Merkel cells, surrounding the base of the taste buds in a ring-like manner, exhibited calmodulin- and S-100-immunoreactive material.

Animals↗
PubMed1992

In vivo fate and scavenger receptor recognition of oxidized lipoprotein[a] isoforms in rats.

High levels of Lp[a] in blood form an independent risk factor for atherosclerosis. Oxidative modification of Lp[a] may be involved in the suggested atherogenic action of Lp[a]. After Cu(2+)-mediated oxidative modification of the 440 kDa and 610 kDa apo[a] isoforms of lipoprotein[a] (Ox-Lp[a]), the in vivo fate was investigated in rats. Ox-Lp[a], when injected into rats, was rapidly removed from the blood circulation by the liver, in which the intrahepatic fate is dependent on the degree of oxidation of the isoforms. Upon oxidation to a slightly increased negative charge of Lp[a], the high molecular weight form of Lp[a] is recognized more efficiently by the Kupffer cells than by the endothelial cells. When the liver uptake of Ox-Lp[a] is blocked by preinjection of polyinosinic acid (poly I), the association of Ox-Lp[a] with the rat heart is increased 20-fold. In vitro studies show that the association and degradation of 125I-labeled Ox-Lp[a] with liver endothelial and Kupffer cells was inhibited by oxidized LDL (Ox-LDL), poly I, or Ox-Lp[a] itself by 60-90%, while only a partial competition was found with acetylated-LDL (up to 25%). In conclusion, after oxidative modification of Lp[a], there is recognition of Ox-Lp[a] by specific oxidized-lipoprotein receptors on liver endothelial and Kupffer cells; the relative importance at low degrees of oxidation of Lp[a] is dependent on the molecular weight of the apo[a] isoforms. Under conditions in which liver uptake is not adequate, the deposition of Ox-Lp[a] in the heart may be of potential pathological importance.

Animals↗
PubMed1992

Dissociation-enhanced lanthanide fluorescence immunoassay of lipoprotein(a) in serum.

Lipoprotein(a), a human serum lipoprotein structurally related to low-density lipoprotein (LDL), contains in addition to apolipoprotein B (apo B) apolipoprotein(a) [apo(a)], a glycoprotein with a strong homology to plasminogen. Lp(a) is a risk factor for coronary heart disease and ischemic cerebrovascular disease. Several immunological techniques are used to quantify Lp(a) in human serum, including radioimmunoassays, rocket immunoelectrophoresis, and enzyme-linked immunosorbent assays. Only the last method is suitable for large-scale clinical studies. We describe another solid-phase immunoassay, based on the dissociation-enhanced lanthanide fluorescence system Delfia (Wallac Oy), and outline the technical details. A polyclonal antiserum directed against Lp(a) was used as the capture antibody. Two kinds of detection antibodies were applied, a polyclonal antiserum against apo B and the polyclonal antiserum against Lp(a). The results agree excellently with the values estimated by rocket immunoelectrophoresis. This assay is easily established, measures Lp(a) in a wide concentration range, and is suitable for screening large populations.

Enzyme-Linked Immunosorbent Assay↗
PubMed1991

Calcium-binding proteins in Aplysia neurons.

1. Calcium (Ca)-binding proteins of neuronal ganglia and of single, identified neurons of the marine mollusk, Aplysia californica, were investigated. Using transblot/45Ca overlays two proteins, at Mr 45,000 and Mr 23,000, with a high Ca-binding ability were found. 2. Western blot analysis revealed that the protein at Mr 45,000 could be separated by 2D-PAGE into proteins with Mr 40,000 and Mr 43,000. The protein at Mr 40,000 immunocross-reacted with antisera directed against parvalbumin and rat calbindin D-28K, indicating a novel Ca-binding protein sharing common antigenic determinants for both proteins. 3. The protein at Mr 23,000 could be separated into a group of proteins with Mr 13,000-20,000 which showed a high degree of similarity to sarcoplasmatic calcium-binding proteins (SCP). 4. We further investigated the protein pattern of single, identified neurons of different electrical activity (bursting, beating, and silent) by 2D-PAGE. Major differences were found in the range of low Mr and low pI, where Ca-binding proteins are generally located. A protein at high concentrations characteristic for silent cells migrated at a position similar to crayfish SCP. 5. The results show that various Ca-binding proteins are characteristic for neurons in the Aplysia nervous system and support the idea that they may effect the electrical behavior of nerve cells.

Action Potentials↗
PubMed1990

[Peroneal weakness].

The 22 year old male patient was admitted because of right sided peroneal nerve palsy two months after transient foot drop on the left side. Both pareses developed under a strict dietary regime leading to a weight loss of about 30 kg within 3 months. Slimmers' paralysis of peroneal nerve was diagnosed after exclusion of polyneuropathy or trauma as possible causes. Complete remission followed after a less restrictive diet.

Adult↗
PubMed1989

[Hypertension].

This 40 year old man had been treated adequately for arterial hypertension over the last 10 years. Within one year this arterial tension rose continuously in spite of treatment. A low blood-potassium value found on routine chemical analysis prompted an investigation on secondary causes for hypertension. The results of a peripheral renin-study were typical for secondary aldosteronism. An abdominal aortography and selective angiography of the renal arteries visualized an intrarenal arterial aneurysm with stenoses as causative factor of the renovascular hypertension. Antihypertensive treatment with an ACE-blocker permitted to normalize the blood-pressure values subsequently.

Adult↗
PubMed1988

Prism adaptation in Parkinson's disease.

Prism adaptation is impaired by lesions in the basal ganglia in non-human primates, suggesting that this area is involved in this form of visuomotor learning. We investigated the ability of patients with Parkinson's disease to prism adapt. Patients and controls wore prisms which deflected vision laterally by 11 degrees. After baseline testing with a localisation task that permitted no feedback about performance accuracy, prism adaptation was tested at 4 minute intervals over a 28 minute trial. All subjects erred initially, reaching too far to the left of the target, but a separate pointing task encouraged adaptation and reaching error decreased at a similar rate in Parkinsonians and controls. Immediately after the prisms were removed, all subjects reached to the right of the target. This negative after effect was present in controls but not patients when assessed 4 minutes later, suggesting that the patients could not maintain the new sensorimotor relationship imposed by the prisms after their removal. This is similar to performance on visuospatial and executive tasks in Parkinsonians, where ongoing behaviour cannot be modulated without external guidance.

Adaptation, Ocular↗
PubMed1987

Differential effects of pentylenetetrazole on ion currents of Aplysia neurones.

The effect of the convulsant drug pentylenetetrazole (PTZ) on separated membrane current components has been studied in identified voltage-clamped Aplysia neurones. External PTZ blocks the voltage-dependent Na+, Ca2+ currents and the delayed rectifier current (INa, ICa and IK,V, respectively). The amplitude of the Ca2+-activated K+ current (IK,Ca) is increased. The amplitude of the fast inactivating K+ current (IA) is transiently increased at low concentrations of PTZ but is depressed at higher concentrations or after long-lasting application of the drug. The effect of PTZ on leakage current (IL) seems to depend on the cell type. In some cells (R-15, L-7, LP-1) IL is decreased while it is increased in other cells (L-11, BL-1, BR-1). PTZ accelerates the inactivation of IK,V and IA and shifts the current-voltage relation of ICa to negative voltages by 5-8 mV. Pressure injection of PTZ into the neurone did not affect IK,V or IK,Ca. Thus PTZ seems to act on the outside of the plasma membrane. The effect of external PTZ on INa, ICa, IK,V and IL is also observed if the internal Ca2+ activity is buffered with EGTA suggesting that an increase in the internal Ca2+ activity is not involved. At -40 mV PTZ induces a tetrodotoxin-insensitive inward current carried by Na+ ions. PTZ transforms the beating pacemaker cell L-11 into a bursting pacemaker and the bursting pacemaker cell R-15 exhibits 'square-wave'-like oscillations of the membrane potential.

Action Potentials↗