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Biomedical subjects

G Dahl

Publications and source records attributed to G Dahl.

At least 73 records · Page 4Linked to original sources
PubMed1981

Tetrodotoxin receptors in membrane fragments: purification from Electrophorus electricus electroplax and binding properties.

A tetrodotoxin receptor-rich preparation of membrane fragments from the electric organ of Electrophorus electricus is described. The specific binding of neurotoxins and freeze-fracture electron microscopy are used as tools to identify and to characterize membrane fractions. Freeze-fracture electron micrographs of the electric organ demonstrate a high density of membrane particles in the extrasynaptic regions. Density gradient fractions show a broad distribution of [3H]tetrodotoxin, [3H]saxitoxin and 125I-labelled bungarotoxin binding in the range of 1.04--1.15 g/ml sucrose densities, with specific neurotoxin binding up to approx. 5 pmol/mg protein. Carrier-free column electrophoresis of density gradient fractions yields a subfraction with tetrodotoxin and alpha-neurotoxin binding up to 30 pmol/mg protein. The major part of the membrane fragments forms vesicles, which are separated by lectin chromatography into an outside-out and inside-out population. The latter represents at least 50% of the material of a density gradient fraction. For the association of tetrodotoxin, a bimolecular kinetic constant kf greater than or equal to 3.10(5) M-1.s-1 is determined. The dissociation constant is k'b = 2.5.10(-2)s-1. These data are in agreement with a thermodynamic dissociation constant of Kd = 20 nM as determined earlier for E. electricus membrane fragments by equilibrium methods (Grünhagen, H.H., Rack, M., Stämpfli, R., Fasold, H. and Reiter, P. (1981) Arch. Biochem. Biophys. 206, in the press). However, these association kinetics of tetrodotoxin binding in vitro are significantly different from kinetics determined electrophysiologically in Rana (Wagner, H.H. and Ulbricht, W. (1975) Pflügers Arch. 359, 297--315) or Xenopus (Schwarz, J.R., Ulbricht, W. and Wagner, H.H. (1973) J. Physiol. 233, 167--194).

Animals↗
PubMed1981

Induction of cell--cell channel formation by mRNA.

Intercellular junctional communication is very common in normal organized tissue. It provides a pathway for transmission of electrical signals, especially in heart muscle, and may be important in differentiation and growth control. The hydrophilic channels which enable cell--cell communication have been well characterized by biophysical methods, and there is now good evidence that they are contained in the nexus (gap junctions). Little, however, is known about the molecular mechanism of biosynthesis of junctional channels. Knowledge in this area has been obtained almost exclusively from experiments with reaggregated cells, a system complicated by the fact that de novo synthesis of channel proteins is obscured by reassembly of pre-existing subunits or utilization of precirsors. To avoid these problems, we have now isolated mRNA from cells that are in the process of making new intercellular nexus with high efficiency, incorporated it via liposomes into communication-defective cells and have shown that the recipient cells established junctional communication.

Animals↗
PubMed1981

Cell junction and cyclic AMP: 1. Upregulation of junctional membrane permeability and junctional membrane particles by administration of cyclic nucleotide or phosphodiesterase inhibitor.

Mammalian cells in culture were exposed to cyclic AMP, dibutyryl cyclic AMP, the phosphodiesterase inhibitor caffeine, or a combination of the last two, while junctional molecular transfer was probed with the series of microinjected, fluorescent-labelled linear molecules Glu, Glu-Glu, Glu-Glu-Glu, and Leu-Leu-Leu-Glu-Glu. The junctional permeability for these molecules increased with each of the agents, most markedly with the dibutyryl cyclic AMP-caffeine combination, as the intracellular cyclic nucleotide concentration rose. The junctional permeability effect developed over several hours. When probed with molecules close to the limit of cell-to-cell channel permeation (the most sensitive setting), the effect was detectable both, as an increase in the (relative) junctional transit rate and as an increase in the number of transferring cell interfaces in the test populations. The number of transferring cell interfaces reached a maximum by 4 hr, when the junctional transit rate, hence the junctional permeability, was still rising. Nonjunctional membrane permeability for the probe molecules, as determined by intracellular fluorescence loss, was not significantly changed (nor was there significant nonjunctional cell-to-cell transfer of molecules before or after the treatments). The rise in junctional permeability was associated with an increase in the number of gap junctional membrane particles, as determined by freeze-fracture electron microscopy: the average size of the particle clusters increased, and the frequency of the clusters increased, particularly that of the smaller (and presumably newer) clusters. This effect was blocked by treatments with the protein synthesis inhibitors cycloheximide or puromycin. These agents caused particle diminution (diminution of cluster frequency but not of average cluster size), with or without cyclic nucleotide. The junctional effects may represent a cyclic AMP-promoted proliferation of cell-to-cell channels. Some physiological implications, in particular, implications for hormone-regulated tissues, are discussed.

Animals↗
PubMed1981

Cell junction and cycle AMP: III. Promotion of junctional membrane permeability and junctional membrane particles in a junction-deficient cell type.

The cyclic nucleotide effect on junction was studied in C1-1D cells, a mouse cancer cell type that fails to make permeable junctions in ordinary confluent culture. Upon administration of cyclic AMP, dibutyryl cyclic AMP, dibutyryl cyclic AMP plus caffeine (db-cAMP-caffeine), or cholera toxin (an adenylate cyclase activator), the cells acquired permeable junctions; they became electrically coupled and transferred fluorescent tracer molecules among each other - a transfer exhibiting the molecular size limit of permeation of normal cell-to-cell channels. The effect took several hours to develop. With the db-cAMP-caffeine treatment, junctional permeability emerged within two hours in one-fifth of the cell population, and within the next few hours in the entire population. This development was not prevented by the cytokinesis inhibitor cytochalasin B. Permeable junctions formed also in two other conditions where the cell-endogenous cyclic AMP level may be expected to increase: serum starvation and low cell density. After three weeks of starving, the cells of serum, a junctional permeability arose in confluent cultures, which on feeding with serum disappeared within two to three days. At low cell density, namely below confluency, the cells made permeable junctions, unstarved. In cultures of rather uniform density, the frequency of permeable junctions was inversely related to the average density, over the subconfluent range; at densities of about 1 X 10(4) cells/cm2, where the cells had few mutual contacts, 80% of the pairs presumed to be in contact were electrically coupled. In cultures with adjoining territories of high (confluent) and low cell density, there was coupling only in the last, and in this low-density state the cells were also capable of coupling with other mammalian cell types (mouse 3T3-BalbC and human Lesch-Nyhan cells).

Animals↗
PubMed1981

Clinical patterns in a behavior modification unit.

The principles and practice of a Behavior Modification Unit in a psychiatric hospital are described. A simple but consistent program of rewards related to privileges is employed together with attention to individual counseling and family therapy. A consecutive series of 56 patients is reported. They had a high frequency of personality disorders, behaviour disorders and past psychiatric treatment irrespective of diagnosis. Improvement was measured in terms of success, three months after discharge, in staying out of hospital and maintaining an independent existence in the community. By this criterion 42 out of 56 patients (75%) were improved. Patients who improved had had less past treatment of various types and this relationship was highly significant. The justification for this type of program is briefly discussed.

Adolescent↗
PubMed1980

De novo construction of cell-to-cell channels.

Nexus (gap junctions), which are considered to contain cell-to-cell channels, are newly formed in uterine smooth muscle during parturition or in response to estrogen treatment of virginal animals. A mRNA preparation was isolated from estrogen-dominated rat myometria and was encapsulated into liposomes. Subsequently the liposomes were fused with cultured cells of a mouse cell line CL-1D. It is established that these tumor cells normally are neither electrically coupled nor do they contain nexus. The cells, however, become electrically coupled a few hours after being loaded with the mRNA preparation. This de novo expression of cell coupling persisted for a litte more than 24 hr after a single loading procedure. Freeze-fracture electron microscopy revealed small nexus-like particle aggregates at the time coupling was present. In control experiments the cells remained noncoupling when the RNA preparation was pretreated with ribonuclease, when cycloheximide was applied to the cells, or when liposomes filled with buffer solution only were used. These data suggest that the de novo expression of cell-to-cell coupling is accomplished by mRNA-induced protein biosynthesis resulting in the formation of cell-to-cell channels.

Animals↗
PubMed1980

The role of Ca2+ as a trigger for membrane fusion.

As revealed by freeze-fracturing, secretory vesicles isolated from pancreatic islet cells fuse when incubated with low concentration of Ca2+. The properties of this process are described and were found to be similar to those investigated with isolated secretory vesicles from different tissue origin. Secretory vesicle fusion is compared mainly with the ionic requirements of insulin secretion by the pancreatic B-cells and exocytosis by other secretory cells.

Calcium↗
PubMed1978

Cold-induced insulin release in vitro: evidence for exocytosis.

Exposure of isolated pancreatic islets (mouse or rat) to low temperature (2 degrees C) evoked a threefold increase in insulin release irrespective of the glucose concentration in the incobation medium. Cold-induced release was transient and rewarming to 37 degrees C restored the sensitivity of B-cells to gluocose stimulation. In islets cooled to 2 degrees C, exocytotic profiles could easily be detected both by thin-section and freeze-fracture electron microscopy. As revealed by the freeze-fracture technique, the number of exocytotic profiles per membrane area was increased three- to fourfold as compared to islet cells incubated at 20 degrees C. This was paralleled by intracellular fusion of secretory vesicles. Cold-induced insulin release was not affected by theophylline, cytochalasin B, omission of extracellular Ca++ or D600. Replacement of extracellular Na+ with choline or sucrose suppressed the increase in insulin release and in frequency of exocytotic profiles recorded after exposure to 2 degrees C. It is suggested that a redistribution of Ca++ from intracellular stores, possibly mediated by an increase in intracellular Na+ triggers exocytosis of insulin granules upon exposure to cold.

Calcium↗
PubMed1978

Fusion of isolated myoblast plasma membranes. An approach to the mechanism.

Fusion of plasma membranes isolated from myoblasts grown in culture has been investigated. 1. Membrane fusion was specifically dependent of Ca2+ at physiological concentrations. However, at higher concentrations of cations, fusion could be triggered not only by Ca2+, but by Mg2+ and Sr2+ as well. 2. The amount of fusion was directly proportional to temperature. 3. Fusion was found to depend on the state of maturation of the myoblast membranes. 4. Experiments with chemically and enzymatically modified membranes and with membranes derived from myoblasts grown in the presence of inhibitors of protein biosynthesis suggest the participation of proteinaceous membrane components in the fusion mechanism.

Animals↗
PubMed1978

Fusion of secretory vesicles isolated from rat liver.

Secretory vesicles isolated from rat liver were found to fuse after exposure to Ca2+. Vesicle fusion is characterized by the occurrence of twinned vesicles with a continuous cleavage plane between two vesicles in freeze-fracture electron microscopy. The number of fused vesicles increases with increasing Ca2+-concentrations and is half maximal around 10(-6)M. Other divalent cations (Ba2+, Sr2+, and Mg2+) were ineffective. Mg2+ inhibits Ca2+-induced fusion. Therefore, the fusion of secretory vesicles in vitro is Ca2+ specific and exhibits properties similar to the exocytotic process of various secretory cells. Various substances affecting secretion in vivo (microtubular inhibitors, local anesthetics, ionophores) were tested for their effect on membrane fusion in our system. The fusion of isolated secretory vesicles from liver was found to differ from that of pure phospholipid membranes in its temperature dependence, in its much lower requirement for Ca2+, and in its Ca2+-specificity. Chemical and enzymatic modifcations of the vesicle membrane indicate that glycoproteins may account for these differences.

Animals↗
PubMed1978

Nexus formation in the myometrium during parturition and induced by estrogen.

The occurence of nexuses (gap junctions) in mouse uterine smooth muscle was found to depend on the hormonal state. As revealed by freeze-fracture electron microscopy, nexuses are virtually absent in virginal and pregnant mice. Abundant, large-sized nexuses were observed in the myometrium during parturition. Estrogen application to virginal mice also induced an increase in number and size of nexuses. Our observations indicate that a new formation of nexuses occurs in differentiated cells. New nexuses may be formed by the confluence of nexus subunits preexisting in the cell membrane or by newly biosynthesized components.

Animals↗