PubMed Health⌕ Search

Biomedical subjects

A Reichenbach

Publications and source records attributed to A Reichenbach.

At least 145 records · Page 8Linked to original sources
PubMed1987

Spatial buffering of potassium by retinal Müller (glial) cells of various morphologies calculated by a model.

In a previous study we found the morphometrical data of rabbit retinal Müller (radial glial) cells to vary greatly with their localization in various parts of the retina. The long cells of the central retina have thinner vitreal processes and smaller endfeet than the short cells of the retinal periphery. This configuration should impair the spatial buffering capacity of the central Müller cells for excess K+ ions. To test this hypothesis, we developed a simple modified model for the calculation of K+ clearance by spatial buffering, diffusion through the extracellular space, and co-operation of both processes. K+ clearance processes were demonstrated to depend greatly on the retinal geometry and Müller cell morphology in different parts of the retina. The efficiency of spatial buffering exhibited an obvious optimum for Müller cells of intermediate length, and decreased very steeply in longer cells. Some conclusions are drawn with respect to retinal physiology. In particular, it is suggested that very long and slender radial glia is unable to perform sufficient K+ clearance preventing long-lasting extracellular [K+] elevations after neuronal activity. Such [K+] elevations could depolarize these glial cells so as to enforce their mitotic division. This mechanism might lead to the perinatal transformation of embryonic radial glia into adult multipolar glia when neuronal activity commences in CNS tissues thicker than the maximal effective length of radial glial cells.

Animals↗
PubMed1987

Quantitative and qualitative morphology of rabbit retinal glia. A light microscopical study on cells both in situ and isolated by papaine.

Rabbit retinal glia was studied by light microscopy of both stained sections of frozen retinae and enzymatically isolated cells. In the vast majority of this tissue, except for a small region around the optic nerve head, the glia consists solely of radial glia, i.e. Müller cells whose morphology was found to depend markedly on their topographic localization within the retina. Müller cells in the periphery are short and have thick vitreal processes bearing a single large endfoot. Central Müller cells are long and slender; through the thickening nerve fibre layer they send vitreal processes which are subdivided into several fine branches ending with multiple small endfeet. Müller cells in the retinal centre are far more closely packed than those in the periphery; everywhere, however, a constant ratio of Müller cells: neurons of about 1:15 was found, except for the juxta-optic nerve head region where this ratio is slightly reduced. Where the central retina reaches a thickness requiring Müller cell lengths of more than 130 micron, additional non-radial glial cells occur within the nerve fibre layer. The majority of these cells seem to be astrocytes. Their number per retinal area increases with the thickening of both the whole retina and the nerve fibre layer. The occurrence of these non-radial glial cells leads to an enhancement of the glia:neuron index in the retinal centre. Possible mechanisms of physiological control of gliogenesis are discussed.

Animals↗
PubMed1986

Postnatal development of radial glial (Müller) cells of the rabbit retina.

Radial glial (Müller) cells were isolated from postnatal rabbit retinae by enzymatic dissociation in papain-containing solution, air-dried, and submitted to Pappenheim's panoptic stain. Morphometric data of these cells were evaluated by light microscopy. During postnatal development, the cells become substantially thicker and shorter, their nuclei lose the rod shape and move more toward scleral layers, and the nucleus-cytoplasm volume relation decreases. Whereas the cell volume increases from birth on, substantial outgrowth of fine side branches within the plexiform layers fails to occur before electrical activity is established there, i.e. after postnatal day 9. A model is proposed relating the growth of sheath-bearing glial processes to local protein synthesis stimulated by external K+ accumulation due to neuronal activity. Early myelinated nerve fibers are suggested to bear mechanical resistance to growing radial glial processes thus causing a splitting of these processes when they enter developing nerve fiber layers.

Animals↗
PubMed1986

Potassium accumulation by the glial membrane pump as revealed by membrane potential recording from isolated rabbit retinal Müller cells.

Müller (glial) cells were isolated from rabbit retinae by papaine and mechanical dissociation. In a special perfusion chamber, the cells were penetrated with a recording electrode. When high-K+ solutions were applied into the environment of the cells by means of a second micropipette, the cell membrane depolarized strongly. During prolonged application of high-K+ solutions, however, there occurred a marked repolarization, and after cessation of high-K+ application, a strong hyperpolarization was observed. Both effects disappeared under the influence of ouabain, suggesting the accumulation of intracellular K+ by an active membrane pump. The data were used for calculation of the membrane's Na+:K+ permeability ratio, the intracellular K+ concentration, the pump rate and the mean pump site density. The calculated values are in good agreement with published data from mammalian astrocytes and are compared with those from amphibian Müller cells.

Animals↗
PubMed1986

Intracellular recordings from isolated rabbit retinal Müller (glial) cells.

Müller (glial) cells were isolated from rabbit retinae by papaine and mechanical dissociation. The cells were fixed on a gelatine-covered glass slide by means of concanavalin A, and the slide was mounted in a perfusion chamber under a light microscope with modified optics. Besides the recording microelectrode, two other micropipettes could be adjusted with their tips near the cell. These micropipettes were used for application of test solutions into the environment of the cells. On application of high K+ solutions, the cell depolarized strongly but during prolonged application there was a marked repolarization. After the end of high K+ application the cells showed a hyperpolarization which was enhanced in both amplitude and duration with prolongation of the K+ exposure. Both repolarization and afterhyperpolarization disappeared under ouabain. Ouabain application itself caused a small reversible depolarization. Na+ free solution caused hyperpolarization. The results suggest the existence of an active membrane pump mechanism in our cells. This pump seems to be electrogenic under our experimental conditions and seems to be activated even in the absence of sodium. The cell membrane is demonstrated to contain a significant Na+ conductance.

Animals↗
PubMed1986

Morphometric parameters of Müller (glial) cells dependent on their topographic localization in the nonmyelinated part of the rabbit retina. A consideration of functional aspects of radial glia.

Morphometric parameters of Müller cells were evaluated by light microscopy both in whole retinae and in enzymatically isolated cells from adult pigmented rabbits. In spite of the marked decrease in cell densities from visual streak to far periphery, a constant glia-neuron ratio of about 1:15 was found in all regions. The volume of individual Müller cells was found to increase strongly when the cells become shorter, i.e. when the retinal centre was compared to the retinal periphery. The contribution of Müller cell volume to the total retinal volume, however, was shown to be constant at about 6%. Long Müller cells have a thin vitreal process and a small vitreal endfoot surface. The consequences of this rule for the proposed function of Müller cells in retinal K+ clearance are discussed with respect to general features of radial glia. It is suggested that foetal radial glial cells too long to perform sufficient K+ clearance are destined to be transformed into 'adult' multipolar glia by mitotic cell division.

Animals↗
PubMed1985

Na+,K+-activated adenosine triphosphatase of isolated Müller cells from the rabbit retina shows a K+ dependence similar to that of brain astrocytes.

Müller (glial) cells from the rabbit retina were isolated by means of papain and mechanical dissociation. Their Na+,K+-adenosine triphosphatase (ATPase) activity was measured using a radiochemical method, and its K+ dependence was determined. In contrast to that of photoreceptors (data from the literature), the Na+,K+-ATPase of Müller cells could be shown to increase its activity greatly when the [K+] was enhanced up to 10 mM. The functional implications of this behaviour for the K+ clearance in the retina are discussed.

Animals↗
PubMed1985

Retinitis-pigmentosa-like tapetoretinal degeneration in a rabbit breed.

By chance, we found a rabbit strain with retinal dystrophy. The eyes of these rabbits were examined by ophthalmoscopy, electroretinography, histology, and cytology--the latter after retina dissociation with papaine. The results suggest this rabbit strain to be a possible animal model for human retinitis pigmentosa.

Animals↗
PubMed1985

Effects of alpha-aminoadipic acid on the glutamate-isolated P III of the rabbit electroretinogram.

alpha-Aminoadipic acid was intravitreally applied to adult rabbits. After 5 h, the retinae of these animals were examined by electroretinography and histochemistry. The retinal Müller cells were extremely swollen, and the electroretinographic slow P III was extinguished. The mass receptor potential was somewhat diminished. The results are consistent with the opinion that the slow P III is the reaction of the Müller cells to the changed external potassium ion concentration caused by the activity of the photoreceptors.

2-Aminoadipic Acid↗
PubMed1985

Morphological variability, lectin binding and Na+,K+-activated adenosine triphosphatase activity of isolated Müller (glial) cells from the rabbit retina.

Rabbit retinal Müller cells were isolated by means of papaine and mechanical dissociation. These cells were shown to have a well preserved morphology and to preserve viability for many hours. Intense wheat germ agglutinin binding occurs on the photoreceptor side of Müller cells, especially in the microvillous region. Rabbit retinal Müller cells have a Na+,K+-activated adenosine triphosphatase activity in the same order of magnitude as brain astroglial cells.

Animals↗
PubMed1985

Morphometric analysis of retinal blood vessels in retinopathia diabetica.

A quantitative investigation of the retinal blood vessels was carried out in 80 diabetics and 20 metabolically healthy controls of the same age and sex distribution. The blood vessels were isolated by trypsinization, stained with PAS, and analyzed by light microscopy. After 1-5 years' duration of diabetes mellitus, capillary lesions in the ocular fundus can be seen microscopically in the slides, but not with a stereomicroscope. In the retinae of persons with normal carbohydrate metabolism, capillary defects were found to a far lesser extent; they were also always localized in the periphery of the retina, whereas the diabetic lesions were localized in the retinal center. In the diabetics, both capillary lesions (e.g., loss of pericytes) and damage of the retinal neurons occurred nearly simultaneously and with the same retinal localization. This suggests that the capillary lesions are not the cause of neuronal degeneration but that both events are caused by the same mechanisms of pathogenesis.

Adult↗
PubMed1984

Changes in membrane-associated proteins during sporulation in Bacillus subtilis.

Membrane proteins from vegetative and sporulating cells of Bacillus subtilis were separated by the two-dimensional gel electrophoresis system using isoelectric focusing and sodium dodecyl sulfate/polyacrylamide gel electrophoresis (O'Farrell technique). Membrane proteins were isolated according to published procedures. The gels were stained with Coomassie blue. Three different concentrations of proteins were analyzed to detect even minor constituents. Over two hundred different membrane proteins were identified in vegetative cells by their isoelectric point (pI) and molecular weight (Mr). Analysis of membrane proteins from cells harvested during and at the end of logarithmic growth (A600 approximately equal to 0.8; T0) and every hour thereafter until T4 showed that in the wild-type strain 55 proteins are degraded mostly at the beginning or sporulation. Many others (76 proteins) are newly synthesized during sporulation. About 16 proteins are synthesized at times during sporulation but again degraded within 1 h or less. Others (uncertain proteins, 65) are degraded and resynthesized again. This observation is in agreement with experiments previously published by Andreoli et al. [Andreoli, A. J., Kao, M., Chui, R., Cabrera, J., and Wong, S. K. S (1981) in Sporulation and Germination (Levinson, H. S., Sonenshein, A. L., and Tipper, D. J., eds) pp. 168-173, American Society for Microbiology, Washington] using Bacillus cereus. Experiments with the early blocked asporogenous mutant JH 649 (spoOF) showed that few proteins (40%) are degraded and even fewer (30%) are newly synthesized between A600 approximately equal to 0.8 and T4. Protease inhibitors (phenylmethylsulfonyl fluoride, EDTA, o-phenanthroline) have no effect on the protein patterns. The experiments presented here show that proteins involved in differentiation in B. subtilis can be identified by the two-dimensional gel electrophoresis system and with the aid of asporogenous mutants. In order to assure that no cytoplasmic proteins are contaminating the membrane preparations, several cytoplasmic enzyme activities have been measured. Their concentration was found to be always below 0.005% of total protein, which is below the level of detection by Coomassie blue staining.

Bacillus subtilis↗
PubMed1984

The glutamate-isolated mass receptor potential of the frog's retina. III. Calcium dependence.

The mass receptor potential of excised frog retinas was isolated by superfusion of the tissue with modified Ringer solutions containing sodium glutamate. The changes in the potential amplitude due to the variation of the calcium concentration were measured. Step by step reduction of the calcium concentration from 2 to 0.05 mM caused a mass receptor potential increase up to threefold; further calcium lowering diminished the amplitudes. Rods and cones, however, seemed to react in different ways to changed calcium concentrations. The responses to red light stimuli and the so-called rapid decay of the glutamate-isolated potentials, both generated mainly by cones, disappeared in calcium free solutions. Both the responses to green light stimuli and the so-called remaining part of mass receptor potentials, however, i.e. the potentials produced mainly by rods, were still larger in calcium free solutions compared to those in 2 mM calcium solutions. Changing the calcium concentration of the solutions altered both the Sodium and the potassium dependence of the mass receptor potential, and that differently for rods und cones. The results are used to support the hypothesis that calcium acts as internal transmitter in vertebrate photoreceptors. This view is confirmed by interpretation and critical comparison of data taken from the literature.

Animals↗
PubMed1983

Quantitative properties of Müller cells in rabbit retina as revealed by histochemical demonstration of NADH-diaphorase activity.

Müller cells in rabbit retina were selectively stained by demonstrating NADH-diaphorase activity. After the sections were measured by light microscopy, the following properties of Müller cells were found: (a) independent of the retinal localization, one Müller cell corresponds with a retinal volume of 15,000 microns 3, i.e., with 11 photoreceptor cells, 2 neurons of the inner nuclear layer, and 0.3-1 ganglion cells; (b) the Müller cell population represents about 6.8% of the total retinal volume; (c) the sorbitol accumulation of Müller cells in diabetic retinopathy is said to be unable to cause osmotic damage.

Animals↗