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H Rehm

Publications and source records attributed to H Rehm.

At least 19 recordsLinked to original sources
PubMed1995

Effects of bradykinin and endothelin-1 on the calcium homeostasis of mammalian cells.

Ca2+ mobilization from intracellular stores is a major event in the signaling cascade triggered by peptide hormone receptors. The transient rise in intracellular free Ca2+ concentration ([Ca2+]i) is well characterized, but little is known about alterations of total cell Ca. Therefore we established a technique to determine changes in total cell Ca during hormone stimulation of 45Ca-loaded cells. Bradykinin and endothelin-1 reduced total cell Ca by up to 56% in HF-15 cells, COS-7 cells, and CHO K1 cells transfected with the rat B2 receptor cDNA. In Rat-1 cells and PC-12 cells, stimulation with endothelin-1 or bradykinin did not result in a net decrease in total cell Ca at physiological extracellular Ca2+ concentration. Decrease in total cell Ca was preceded by an increase in [Ca2+]i and blunting of the transient rise in [Ca2+]i by a Ca2+ chelator prevented the hormone-induced decrease in total cell Ca. Previous reduction of total cell Ca by one hormone suppressed the transient rise in [Ca2+]i induced by another. The data present evidence that the hormones bradykinin and endothelin-1 are capable of switching off the Ca(2+)-mobilizing signal transduction pathway in a cell by depleting intracellular Ca stores. This process is accompanied by a significant reduction of total cell Ca.

Animals↗
PubMed1993

Photoaffinity labeling of the NMDA receptor.

The structure of NMDA receptors in situ has been probed with the novel photoaffinity ligand 125I-CGP 55802A. By covalently linking the radioactive high-affinity photolabel to NMDA receptors in bovine brain we have identified a protein of 175 kDa associated with the binding site for NMDA receptor agonists and competitive antagonists. Based on its molecular size the photolabeled protein is likely to correspond to the NR2A and/or NR2B subunit. The photoaffinity ligand will permit the assessment of regulatory changes in NMDA receptor subunit expression.

Affinity Labels↗
PubMed1991

Voltage-gated K+ channels of the mammalian brain.

Research on voltage-gated K+ channels of the mammalian brain has seen a flood of new data in the last 2 years. A genetic approach, based on the Shaker mutation of Drosophila, led to cDNA clones for mammalian voltage-gated K+ channels. K+ channel proteins were detected independently and purified with the help of channel specific toxins. From these studies the structure of two families of mammalian K+ channels emerged. One family is defined molecularly by the sequence homology of its members, the other by binding sites for the snake toxin dendrotoxin. The two families have several members in common. The voltage-gated K+ channels of mammalian brain are oligomers of glycosilated peptides of 65-95 kDa. The primary structure of these subunits is characterized by six to eight potential transmembrane regions, including the S4 region, the voltage-sensor of the channels. Associated with at least some K+ channels are 38- and 42-kDa peptides of unknown function. The channels give rise to non- or slow-inactivating K+ currents that are regulated through phosphorylation by both cAMP-dependent and an endogenous kinase.

Animals↗
PubMed1991

Potassium channels and epilepsy: evidence that the epileptogenic toxin, dendrotoxin, binds to potassium channel proteins.

Dendrotoxin-I, a component of the venom of the black mamba snake, Dendroaspis polylepsis, was used to affinity purify a potassium channel from bovine brain. This dendrotoxin-I binding protein was composed of several subunits with molecular weights of 35,000, 38,000, 42,000 and 74,000. Partial sequence resulting from Edman degradation of the N-terminus of the 74 kDa subunit was identical to the predicted amino acid sequence of the N-terminus of a protein encoded by a mouse/rat homologue of the Shaker gene family of potassium channels, MK2/RBK2 (RCK5). Polyclonal antibodies raised against synthetic peptides derived from the predicted amino acid sequence of another member of this family, MK1, recognized this 74 kDa subunit. Due to extensive amino acid sequence identity between MK2 and MK1, it is likely that antibodies recognized epitopes common to both. Thus, from an immunological standpoint, either MK1, MK2, or both channel proteins could have been present in this 74 kDa band on protein blots. Closely related K+ channels in bovine brain could have copurified based on their affinity for dendrotoxin-I (DTX-I). DTX-I was shown to inhibit MK1 currents in a time and voltage independent fashion. Physiological and molecular evidence indicates the existence of many types of DTX sensitive potassium channels in the mammalian brain, however, our protein sequencing of the 74 kDa subunit has detected the presence of only one unique N-terminal sequence, identical to MK2. The possible reason for the appearance of this discrepancy is discussed. This paper represents the first report identifying one dendrotoxin binding protein in bovine brain tissue (BK2) as a delayed rectifier type of potassium channel.

Amino Acid Sequence↗
PubMed1990

["Adolescent crisis" diagnosis reflected in the Rorschach diagnosis].

In clinical practice the problem of diagnosis and illness concept in adolescent psychiatry is related to the highly important consequences concerning various therapeutic approaches. Though the socalled diagnostic category "adolescent crisis" is not a real psychiatric one it serves for this purpose. The first part of this report is a review on the development and common use of this concept. The second part is an attempt to investigate the phenomena of adolescent disorder which constitute the diagnosis. For this research we use the Rorschachtest based on the study of 10 catamnestically controlled single cases. Evidence for the prognostic value of the Rorschach-results is-with respect to the question "adolescent crisis or schizophrenia?--the patients' clinical state and Rorschach-findings 5 years after their first hospitalization. In addition an attempt is made for find a Rorschach-syndrome which is related to the diagnosis "adolescent crisis".

Adolescent↗
PubMed1989

Dendrotoxin-binding brain membrane protein displays a K+ channel activity that is stimulated by both cAMP-dependent and endogenous phosphorylations.

The purified protein that binds the K+ channel ligands dendrotoxin I and mast cell degranulating peptide can be phosphorylated by cAMP-dependent protein kinase and by an endogenous protein kinase, which may be a specific K+ channel kinase. Phosphorylations take place on the toxin-binding subunit, a polypeptide of 76-80 kDa. Phosphorylation by both kinases leads to activation of the reconstituted dendrotoxin-sensitive K+ channel.

Animals↗
PubMed1989

Immunological evidence for a relationship between the dendrotoxin-binding protein and the mammalian homologue of the Drosophila Shaker K+ channel.

Polyclonal antibodies were raised against two synthetic peptides from different parts of the predicted amino acid sequence of the mouse homologue (MBK1) of the Drosophila Shaker K+ channel. The antibodies recognized the toxin-binding subunit of the dendrotoxin-binding proteins from rat and bovine brain. The results suggest that the dendrotoxin-binding protein is related to the expression products of the mammalian homologue of the Shaker gene.

Animals↗
PubMed1989

Enzymatic deglycosylation of the dendrotoxin-binding protein.

The neuronal membrane protein which binds the K+-channel ligands dendrotoxin, mast cell degranulating peptide, and beta-bungarotoxin was purified from rat brain membranes. When analysed on 10% SDS gel electrophoresis, the purified protein contained two peptides: the toxin-binding subunit of apparent Mr 90,000 and another peptide of Mr 38,000. Neuraminidase treatment reduced the Mr of the toxin-binding subunit to 70,000. Glycopeptidase F gave a further reduction to Mr 65,000. In contrast, the peptide of Mr 38,000 showed no change in Mr upon treatment with neuraminidase and/or glycopeptidase F. It is concluded that the toxin-binding subunit of the dendrotoxin-binding protein, a presumptive K+ channel, is a sialated membrane protein with a peptide core of, at most, Mr 65,000.

Amidohydrolases↗
PubMed1989

Molecular properties of potassium channels.

The paper describes the molecular pharmacology and biochemistry of three types of K+ channels, the calcium-activated potassium channels, ATP-regulated potassium channels and voltage-sensitive potassium channels.

Adenosine Triphosphate↗
PubMed1988

Fractionation of synaptophysin-containing vesicles from rat brain and cultured PC12 pheochromocytoma cells.

Synaptophysin is a transmembrane glycoprotein of neuroendocrine vesicles. Its content and distribution in subcellular fractions from cultured PC12 cells, rat brain and bovine adrenal medulla were determined by a sensitive dot immunoassay. Synaptophysin-containing fractions appeared as monodispersed populations similar to synaptic vesicles in density and size distribution. Membranes from synaptic vesicles contained approximately 100-times more synaptophysin than chromaffin granules. In conclusion, synaptophysin is located almost exclusively in vesicles of brain and PC12 cells which are distinct from dense core granules.

Adrenal Medulla↗
PubMed1988

Identification of synaptophysin as a hexameric channel protein of the synaptic vesicle membrane.

The quaternary structure and functional properties of synaptophysin, a major integral membrane protein of small presynaptic vesicles, were investigated. Cross-linking and sedimentation studies indicate that synaptophysin is a hexameric homo-oligomer, which in electron micrographs exhibits structural features common to channel-forming proteins. On reconstitution into planar lipid bilayers, purified synaptophysin displays voltage-sensitive channel activity with an average conductance of about 150 picosiemens. Because specific channels and fusion pores have been implicated in vesicular uptake and release of secretory compounds, synaptophysin may have a role in these processes.

Animals↗
PubMed1988

Existence of different populations of the dendrotoxin I binding protein associated with neuronal K+ channels.

The binding sites of dendrotoxin I, mast cell degranulating peptide, and beta-bungarotoxin are thought to be associated with neuronal K+ channels. The different binding sites seem to reside on the same molecular assembly as each toxin can allosterically inhibit the binding of the others. Affinity chromatography on a beta-BTX Aca 22 affinity column has shown that there is an heterogeneous population of dendrotoxin I binding proteins. Two subtypes were separated: DTXI binding proteins with low affinity for beta-BTX (60-70% of total) and DTXI binding proteins with high affinity for beta-BTX (30-40% of total). Binding of 125I-DTXI and 125I-MCD to the former subtype is inhibited by beta-BTX with a low affinity (IC50 = 560 nM), while inhibition at the latter subtype occurs with a high affinity (IC50 = 10-16 nM). The DTXI binding subtype with low affinity for beta-BTX contains most (85-90%) of the binding sites for 125I-MCD.

Animals↗
PubMed1988

The receptor site for the bee venom mast cell degranulating peptide. Affinity labeling and evidence for a common molecular target for mast cell degranulating peptide and dendrotoxin I, a snake toxin active on K+ channels.

The mast cell degranulating peptide (MCD) and dendrotoxin I (DTXI) are two toxins, one extracted from bee venom, the other one from snake venom, that are thought to act on voltage-sensitive K+ channels. Binding sites for the two toxins have been solubilized. The solubilized sites were stable and retained their high affinity for 125I-DTXI and 125I-MCD (Kd approximately equal to 100 pM). Interactions were found between MCD and DTXI binding sites in the solubilized state, establishing that the two different toxins act on the same protein complex. This conclusion was strengthened by the observations (i) that conditions of solubilization that eliminated 125I-MCD binding activity also eliminated 125I-DTX binding activity while both types of activities were preserved in the presence of K+ or Rb+ and (ii) that binding components for the two types of toxins had similar sedimentation coefficients and copurified in partial purifications. A component of the receptor protein for 125I-MCD has been identified; it has a Mr of 77,000 +/- 2000. This polypeptide was similar to or identical in molecular weight with that which serves as a receptor for DTXI (Mr 76,000 +/- 2000).

Animals↗
PubMed1988

Inhibition of beta-bungarotoxin binding to brain membranes by mast cell degranulating peptide, toxin I, and ethylene glycol bis (beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid.

The presynaptically active snake venom neurotoxin beta-bungarotoxin (beta-Butx) is known to affect neurotransmitter release by binding to a subtype of voltage-activated K+ channels. Here we show that mast cell degranulating (MCD) peptide from bee venom inhibits the binding of 125I-labeled beta-Butx to chick and rat brain membranes with apparent Ki values of 180 nM and 1100 nM, respectively. The mechanism of inhibition by MCD peptide is noncompetitive, as is inhibition of 125I-beta-Butx binding by the protease inhibitor homologue from mamba venom, toxin I. Beta-Butx and its binding antagonists thus bind to different sites of the same membrane protein. Removal of Ca2+ by ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid inhibits the binding of 125I-beta-Butx by lowering its affinity to brain membranes.

Animals↗