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J Bormann

Publications and source records attributed to J Bormann.

53 records · Page 3Linked to original sources
PubMed1988

Patch-clamp study of gamma-aminobutyric acid receptor Cl- channels in cultured astrocytes.

The membrane channels operated by gamma-aminobutyric acid (GABA) were studied in cultured astrocytes from rat cerebral hemispheres by using patch-clamp techniques. The channel properties appeared to be very similar, in many respects, to those present in neuronal cell membranes. The Cl- -selective channels were activated after the sequential binding of two GABA molecules to the receptor, as deduced from the slope of the dose-response curve. Single-channel currents displayed multiple conductance states of 12 pS, 21 pS, 29 pS, and 43 pS, with the main-state conductance being 29 pS. The gating properties could be described by a sequential reaction scheme for agonist-activated channels. GABA-induced whole-cell currents were potentiated by the benzodiazepine receptor agonist diazepam and also, to a lesser extent, by methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate an inverse agonist. In neurons and chromaffin cells, methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate reduces the sensitivity of the GABA receptor, indicating that neuronal and glial GABA/benzodiazepine receptor--Cl- channel complexes are different. Glial GABA receptor channels could be of functional importance in buffering extracellular Cl- in the cleft of the GABAergic synapse.

Animals↗
PubMed1987

Mechanism of anion permeation through channels gated by glycine and gamma-aminobutyric acid in mouse cultured spinal neurones.

1. The ion-selective and ion transport properties of glycine receptor (GlyR) and gamma-aminobutyric acid receptor (GABAR) channels in the soma membrane of mouse spinal cord neurones were investigated using the whole-cell, cell-attached and outside-out patch versions of the patch-clamp technique. 2. Current-voltage (I-V) relations of transmitter-activated currents obtained from whole-cell measurements with 145 mM-Cl- intracellularly and extracellularly, showed outward rectification. In voltage-jump experiments, the instantaneous I-V relations were linear, and the steady-state I-V relations were rectifying outwardly indicating that the gating of GlyR and GABAR channels is voltage sensitive. 3. The reversal potential of whole-cell currents shifted 56 mV per tenfold change in internal Cl- activity indicating activation of Cl(-)-selective channels. The permeability ratio of K+ to Cl- (PK/PCl) was smaller than 0.05 for both channels. 4. The permeability sequence for large polyatomic anions was formate greater than bicarbonate greater than acetate greater than phosphate greater than propionate for GABAR channels; phosphate and propionate were not measurably permeant in GlyR channels. This indicates that open GlyR and GABAR channels have effective pore diameters of 5.2 and 5.6 A, respectively. The sequence of relative permeabilities for small anions was SCN- greater than I- greater than Br- greater than Cl- greater than F- for both channels. 5. GlyR and GABAR channels are multi-conductance-state channels. In cell-attached patches the single-channel slope conductances close to 0 mV membrane potential were 29, 18 and 10 pS for glycine, and 28, 17 and 10 pS for GABA-activated channels. The most frequently observed (main) conductance states were 29 and 17 pS for the GlyR and GABAR channel, respectively. 6. In outside-out patches with equal extracellular and intracellular concentrations of 145 mM-Cl-, the conductance states were 46, 30, 20 and 12 pS for GlyR channels and 44, 30, 19 and 12 pS for GABAR channels. The most frequently occurring main state was 46 pS for the GlyR and 30 pS for the GABAR channel. 7. Single-channel conductances measured in equal 140 mM concentrations of small anions on both membrane faces revealed a conductance sequence of Cl- greater than Br- greater than I- greater than SCN- greater than F- for both channels. This is nearly the inverse sequence of that found for the permeability of these ions indicating the presence of binding sites for ions in the channel.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1985

gamma-Aminobutyric acid receptor channels in adrenal chromaffin cells: a patch-clamp study.

We have studied membrane channels activated by gamma-aminobutyric acid (GABA) in adrenal medullary chromaffin cells by using patch-clamp techniques. These channels share many properties with GABA-receptor channels in the central nervous system. They are chloride-selective, blocked by the GABA antagonist bicuculline, and reversibly desensitized at high GABA concentrations. The dose-response curve has a slope of 2 in the Hill plot, indicating a bimolecular binding reaction of GABA to the receptor. Single-channel currents display multiple conductance states as do glycine-activated chloride channels in mouse spinal neurons. Gating properties of GABA-activated channels, as described by a sequential model for agonist-activated channels, are similar to gating properties in central neurons. GABA-induced currents are potentiated by diazepam, indicating that anxiolytic drugs like the benzodiazepines might be involved in the regulation of anxiety states in the peripheral nervous system.

Animals↗
PubMed1983

Three types of acetylcholine-induced single channel currents in clonal rat pheochromocytoma cells.

Single channel currents induced by acetylcholine were recorded from nerve growth factor-differentiated clonal rat pheochromocytoma (PC12) cells by using the patch-clamp technique. Inward current amplitudes were heterogeneous and could be related to three classes of unitary current. The three current-voltage relations were linear for patch membrane potentials ranging from -50 mV to -120 mV. At 22 degrees C, conductances of 22 pS, 31 pS and 39 pS were obtained. The extrapolated reversal potential for the channels was 0 mV and the mean open time approximately 10-20 ms. These results may indicate that PC12 cells possess three types of acetylcholine receptor channels.

Acetylcholine↗
PubMed1983

Patch-clamp measurements of elementary chloride currents activated by the putative inhibitory transmitter GABA and glycine in mammalian spinal neurons.

Methods for measuring whole-cell and unitary Cl- currents in the soma membrane of cultured spinal cord neurons by the patch-clamp technique are described. To separate single channel Cl- currents activated by the two putative inhibitory transmitters GABA and glycine from other membrane currents, isotonic KCl pipette solutions are used for measurements on "cell-attached" membrane patches. To isolate unitary Cl- currents in "cell-free" membrane patches, symmetrical, isotonic Tris Cl- solutions are used in both the pipette and the bath. Single Cl- channels are opened following binding of two agonist molecules to their respective receptors. The gating behavior of single receptor-channel complexes is described in terms of the activation and desensitization mechanism suggested originally by del Castillo and Katz (1957) and Katz and Thesleff (1957).

Animals↗
PubMedDate not supplied

Measurement of fatigue in HIV-positive adults: reliability and validity of the Global Fatigue Index.

Fatigue is among the most common and distressing symptoms in patients with HIV/AIDS. Little is known about the clinical assessment of fatigue, especially in patients using highly active antiretroviral regimens. The purpose of this study was to evaluate the psychometric properties of the Global Fatigue Index (GFI) in a community-based sample of 209 patients with HIV/AIDS. The GFI is a measure that quantifies five dimensions of fatigue from the Multidimensional Assessment of Fatigue instrument into one score. To assess construct validity, the study included measures of depression, perceived stress, activities of daily living (ADLs), health behaviors, and clinical markers. Cronbach's alpha was calculated for internal consistency reliability, and factor analysis and bivariate correlations were conducted. The GFI was found to be easily self-administered, reliable, and a valid measure of overall fatigue burden in an HIV population. This instrument may be used by clinicians and researchers for assessing fatigue.

Adult↗
PubMedDate not supplied

Organotypic slice culture of the mammalian retina.

Vertical slices of 6-day postnatal (P6) rat retina were cut at a thickness of 100 microns and cultured using the roller-tube technique. After 14-21 days in vitro there was significant distortion of normal retinal architecture, but localized areas of the slices showed the typical pattern of layering of mature retina. The following immunocytochemical markers were used to characterize the different retinal cell types: antibodies against protein kinase C (PKC), calcium binding protein (CabP 28kD), neurofilaments (NF), glia-specific antibodies (GFAP, vimentin), and transmitter-specific antibodies (GABA, TH). The expression of these markers was compared in P6 retina, adult retina, and slice culture. To further characterize the cultured cells, patch-clamp recordings were performed in combination with intracellular injection of Lucifer Yellow (LY). Transmitter- and voltage-gated membrane currents were recorded from morphologically identified neurons. The experiments show that a mammalian slice culture can be used to study differentiation and function of retinal cell types.

Animals↗
PubMedDate not supplied

Expression of glycine receptor subunits and gephyrin in single bipolar cells of the rat retina.

We studied the expression of glycine receptor (GlyR) subunits and gephyrin in the adult rat retina. Reverse transcribed RNA was amplified by polymerase chain reaction (RT-PCR) with primers designed to recognize GlyR alpha 1, alpha 2, alpha 3, beta subunits, and gephyrin. Using RNA isolated from the whole retina, signals for all four GlyR subunits and gephyrin could be observed. In rod bipolar cells, in contrast, we detected a subset of GlyR subunits, alpha 1 and beta, and no gephyrin. Patch-clamp recording employing two subtype-specific blockers of the GlyR, picrotoxinin and cyanotriphenylborate (CTB), indicated that the GlyR in rod bipolar cells is a heteromeric protein composed of the alpha 1 and beta subunit. Moreover, the absence of detectable amounts of gephyrin mRNA suggests that the anchor protein is not required for the function of GlyRs in rod bipolar cells.

Animals↗
PubMedDate not supplied

Synaptic organization of an organotypic slice culture of the mammalian retina.

Vertical slices of postnatal day 6 (P6) rat retina were cut and cultured using the roller-tube technique. The organotypic differentiation during a culture period of up to 30 days has been described in a previous study (Feigenspan et al., 1993a). Here we concentrated on the synaptic organization in the retinal slice culture. Electron microscopy revealed the presence of ribbon synapses in the outer plexiform layer and conventional and ribbon synapses in the inner plexiform layer. Immunofluorescence with antibodies that recognize specific subunits of GABAA or glycine receptors revealed a punctate distribution of the receptors. They were aggregated in "hot spots" that correspond to a concentration of receptors at postsynaptic sites. Different isoforms of GABAA and glycine receptors occurred in the slice cultures. The experiments show that there is a differentiation of synapses and a diversity of transmitter receptors in the slice cultures that is comparable to the in vivo retina.

Animals↗
PubMedDate not supplied

GABA immunoreactivity in the human cerebellar cortex: a light and electron microscopical study.

The distribution of gamma-aminobutyric acid (GABA) in surgical samples of human cerebellar cortex was studied by light and electron microscope immunocytochemistry using a polyclonal antibody generated in rabbit against GABA coupled to bovine serum albumin with glutaraldehyde. Observations by light microscopy revealed immunostained neuronal bodies and processes as well as axon terminals in all layers of the cerebellar cortex. Perikarya of stellate, basket and Golgi neurons showed evident GABA immunoreactivity. In contrast, perikarya of Purkinje neurons appeared to be negative or weakly positive. Immunoreactive tracts of longitudinally- or obliquely-sectioned neuronal processes and punctate elements, corresponding to axon terminals or cross-sectioned neuronal processes, showed a layer-specific pattern of distribution and were seen on the surface of neuronal bodies, in the neuropil and at microvessel walls. Electron microscope observations mainly focussed on the analysis of GABA-labelled axon terminals and of their relationships with neurons and microvessels. GABA-labelled terminals contained gold particles associated with pleomorphic vesicles and mitochondria and established symmetric synapses with neuronal bodies and dendrites in all cortex layers. GABA-labelled terminals associated with capillaries were seen to contact the perivascular glial processes, basal lamina and endothelial cells and to establish synapses with subendothelial unlabelled axons.

Aged↗
PubMedDate not supplied

Activation of multiple-conductance state chloride channels in spinal neurones by glycine and GABA.

In the mammalian central nervous system, glycine and gamma-aminobutyric acid (GABA) bind to specific and distinct receptors and cause an increase in membrane conductance to CI- (refs 5-7). Neurones in various regions of the nervous system show differential sensitivity to glycine and GABA; thus GABA and glycine receptors are spatially distinct from one another. However, on the basis of desensitization experiments on spinal cord neurones, it was suggested that the receptors for glycine and GABA may share the same CI- channel. We now report that in small membrane patches, isolated from the soma of spinal neurones, both receptor channels display several (multiple) conductance states. Two of the states are common to both receptor channels. However, the most frequently observed 'main conductance states' of the GABA and glycine receptor channels are different. Both channels display the same anion selectivity. We propose that one class of multistate CI- channel is coupled to either GABA or glycine receptors. The main conductance state adopted by this channel is determined by the receptor to which it is coupled.

Animals↗