Search PubMed⌕ Search

Biomedical subjects

W Hoss

Publications and source records attributed to W Hoss.

At least 37 records · Page 2Linked to original sources
PubMed1986

Regional distribution of muscarinic receptors preferring gallamine in the rat brain.

The regional distribution of muscarinic receptors recognized by the antagonist gallamine was determined autoradiographically by the ability of gallamine to reduce the binding of [3H]quinuclidinyl benzilate in rat brain slices. The inhibition data obtained from indirect binding assays on whole slices indicated that gallamine distinguished at least two sites with differing affinities. Analysis using a two-site model gave Kh = 0.6 microM, K1 = 10 microM. The regions of highest and lowest affinity for gallamine were apparent qualitatively by visual inspection of the autoradiograms. A number of regions in coronal sections at three different levels were compared by microdensitometry. Gallamine possessed greater overall affinity for the diencephalon and brainstem than for the forebrain. Within the forebrain, the septal nucleus was unique in that it displayed high affinity for gallamine. Within the brainstem, the superior colliculus had the greatest proportion of sites with high affinity for gallamine. In general, the binding profile of gallamine was opposite to that of the antagonist pirenzepine and similar to that of the agonist carbachol, suggesting that gallamine is selective for M2 muscarinic receptors.

Animals↗
PubMed1986

Characterization of noncholinergic nicotine receptors on human granulocytes.

The noncholinergic nicotine receptor on leukocytes identified earlier [Davies et al., Molec. Cell. Biochem. 44, 23 (1982)] was further characterized. Structure-activity relationships showed that a pyrrolidine ring containing a basic N atom is an important structural feature for ligands that bind to the receptor. Accordingly, the carcinogenic component of tobacco smoke, N-nitrosonornicotine, does not bind to the receptor. The stereoselectivity for the d-isomer, which was confirmed using [3H]d-nicotine as a ligand, together with the absolute configurational relationship between d-nicotine and L-proline, suggested that basic peptides containing proline as the N-terminal amino acid would bind to the receptor. The finding that Pro-Lys-Pro-Arg, which has been reported to inhibit granulocyte phagocytosis, bound to the receptor with an IC50 value of 3.5 microM is compatible with this idea. An increase in receptor binding, which was observed in the presence of plasma, could be ascribed to bicarbonate. The presence of bicarbonate in the binding assay, even when the pH of the buffer was carefully controlled, resulted in an increase (approximately 2-fold) in the apparent number of receptors without affecting the Kd value significantly. Increasing the pH of the buffer in the absence of bicarbonate also increased receptor binding, suggesting that bicarbonate may increase receptor binding by its known ability to increase intracellular pH at constant extracellular pH. Preincubation of cells with d-nicotine under certain conditions reduced the subsequent binding of [3H]d-nicotine to the receptor.

Binding Sites↗
PubMed1986

Mechanism of phospholipase A2-induced conduction block in bullfrog sciatic nerve. I. Electrophysiology and morphology.

The effects of exogenously added phospholipase A2 (PLA2) and its hydrolytic products in isolated bullfrog sciatic nerve were investigated. Nerves were pretreated for 3 h with a dose of trypsin which did not affect conduction in order to enhance penetration of the added agents. Treatment of nerves with beta-glucosidase, neuraminidase or chymotrypsin had no effect on conduction. Whereas incubation of the nerves with normal Ringers for 2 h had no significant effect on conduction, incubation with PLA2 in Ringers caused decrements in the height of the compound action potential in a dose-related manner. In addition, incubation of the nerves with 10 mg/ml lysolecithin, arachidonic acid, or docosahexaenoic acid caused marked decrements in the height of the compound action potential. Electron microscopic analysis of nerves after each treatment which caused conduction block revealed varying levels of myelin damage. Although myelin was damaged at the paranodal and/or internodal region, depending on the agents used, the axonal membrane appeared to be intact at the ultrastructural level. It was concluded that the block in conduction resulting from PLA2 was due to the formation of lysolecithin and long chain polyunsaturated fatty acids.

Animals↗
PubMed1986

Mechanism of phospholipase A2-induced conduction block in bullfrog sciatic nerve. II. Biochemistry.

The biochemical changes associated with conduction block following exogenous application of purified phospholipase A2 to bullfrog sciatic nerves were investigated. Nerves were treated with concentrations of phospholipase A2 needed to produce at least a 50% decrease in the compound action potential after a 2-2 1/2 h incubation. This phospholipase A2-induced conduction block was associated with lipid hydrolysis, depletion of high energy phosphates and decreases in [3H]saxitoxin binding. Forty-two percent of the nerve phosphatidylcholine and 45% of the nerve phosphatidylethanolamine were hydrolyzed. [3H]Saxitoxin binding was decreased by 85% in association with conduction block attained with phospholipase A2 incubation. There were significant decrements in adenosine triphosphate levels (-58%) and in phosphocreatine levels (-78%), but no difference in the specific activities of these phosphate compounds. It is concluded that a number of mechanisms can account for the conduction failure resulting from phospholipase A2, including disruption of sodium channels needed for propagation of regenerative nerve impulses and the depletion of high energy phosphates needed to maintain ionic gradients.

Adenine Nucleotides↗
PubMed1986

Inactivation of depolarization-induced calcium uptake in rat brain synaptosomes.

The inactivation of depolarization-induced Ca uptake into rat brain synaptosomes was demonstrated biochemically by comparing 45Ca fluxes after various intervals of predepolarization achieved by abruptly increasing [K+]o. The chemical composition of the medium was maintained throughout the predepolarization and Ca uptake steps. Under these conditions, inactivation was dependent on depolarization, i.e., basal unstimulated Ca uptake in the presence of 5 mM [K+]o did not inactivate. Inactivation of stimulated Ca uptake was dependent on the predepolarization interval, moderately dependent on [Ca]o and relatively independent of membrane potential, i.e., [K+]o and ions such as Ni2+ and Co2+ that blocked Ca uptake. Both cinnarizine and lidoflazine blocked stimulated Ca uptake in a concentration-dependent manner without affecting the % inactivation. Although the amount of stimulated uptake increased greatly between 10 and 30 degrees C, the % inactivation was unaffected by temperature. These findings suggest that inactivation of the presynaptic Ca uptake is an intrinsic property of the channel independent of calcium uptake.

Animals↗
PubMed1985

Characterization of muscarinic cholinergic receptors in the brains of copper-deficient rats.

In order to assess a possible role for copper as a regulator of muscarinic receptors in vitro, the receptor was characterized in rats made copper deficient by a dietary regimen. In forebrain regions there was a decrease in both the affinity of the receptors for [3H]-1-quinuclidinyl benzilate and the density of receptors in the copper-deficient animals compared with control animals. Copper treatment in vitro of homogenates from deficient animals did not reverse the in vivo effects on antagonist binding but, rather, decreased receptor occupancy and ligand affinity in a manner similar to copper treatment of control homogenates. Minimally deficient rats displayed very similar changes in receptor properties compared with the more severely deficient animals. Minimal copper deficiency produced robust effects on the binding of agonists, increasing ID50 and derived dissociation constants. The addition of copper to the assay medium caused an apparent reversal of the in vivo effect of copper deficiency on agonist binding, decreasing ID50 and derived dissociation constants to values near those observed with homogenates from normal animals in the presence of copper. Since copper deficiency has dramatic effects on both receptor number and the binding of agonists to muscarinic receptors in the central nervous system, it is suggested that copper, because of its ability to form complexes with some proteins, may have an endogenous role in the regulation of the receptor.

Animals↗
PubMed1984

Nicotine-induced membrane perturbation of intact human granulocytes spin-labeled with 5-doxylstearic acid. Correlation with chemotaxis.

The effects of nicotine on intact human granulocytes were examined, using 5-doxylstearic acid as a spin probe. At micromolar concentrations, (-)-nitocine produces a membrane perturbation in granulocytes not observable with oriented lipid bilayers. The effect, which is stereoselective for the (-)-isomer, occurs at concentrations of nicotine that bind to noncholinergic nicotine receptors on granulocytes and which are present in the blood after smoking. At comparable concentrations, (-)-nicotine modulates granulocyte chemotaxis towards a chemotactic peptide in a stereospecific and dose-dependent manner. Cotinine, the major metabolite of nicotine, does not bind to the receptor, does not produce the membrane perturbation observed with nicotine, and has no effect on chemotaxis. These results suggest that (-)-nicotine present in the blood after smoking binds to a receptor on granulocytes, perturbs granulocyte membranes and modulates chemotaxis.

Cell Membrane↗
PubMed1984

Effects of copper on the binding of agonists and antagonists to muscarinic receptors in rat brain.

Studies were performed to assess the effects of copper treatment in vitro on muscarinic binding parameters in rat brain homogenates. Brainstem, an area low in copper, was found to be insensitive to copper treatment as compared to forebrain, a region of relatively high copper content. Inclusion of 3 microM copper in forebrain homogenates decreased the number of sites seen by [3H]-l-quinuclidinyl benzilate (QNB) by 40-50%. Copper-enhanced displacement of bound QNB was noted for agonists and antagonists. Both ligands showed maximal effects at 6 microM copper, although quantitative differences could be determined at any copper level. At levels of maximal effect, the increase in QNB displacement was greater than or less than 50% for agonists and antagonists respectively. Two-site analyses of carbamylcholine (CCH) binding showed that the addition of 1 microM copper to forebrain homogenates increased the percentage of high affinity sites (alpha) from 42 to 70%. The IC50 decreased from 3.1 to 1.7 microM, but the dissociation constants for the high and low affinity sites were not changed. The effect of added copper on CCH binding to muscarinic receptors was reversible with the addition of the copper-chelating agent triethylene tetramine.

Animals↗
PubMed1984

Calcium channel activity in rat brain synaptosomes: effects of neuroleptics and other factors regulating phosphorylation and transmitter release.

Neuroleptic drugs inhibit depolarization-induced Ca uptake in nerve endings, having IC50 values in the micromolar range. Dopamine and a variety of other substances including opiates and PGE1 are inactive. The effect is probably not mediated by the interaction of the neuroleptics with calmodulin, which itself is a potent inhibitor of stimulated Ca uptake. Dibutyryl cyclic AMP, but not fluoride, increases K+-stimulated Ca uptake. Phosphatidic acid, which is an intermediate in transmitter-stimulated phosphatidylinositol turnover, acts as a Ca ionophore in nerve endings and enhances K+-stimulated Ca uptake at a relatively low concentration. Carbamyl choline, a known stimulator of phosphatidylinositol turnover, did not, however, cause a significant increase in K+-stimulated Ca uptake. Treatment of the nerve ending fraction with relatively small amounts of phospholipase A2 greatly inhibited depolarization-induced Ca uptake, demonstrating the importance of phospholipids for the functioning of the potential-dependent Ca channel in nerve endings. These studies suggest that the regulation of voltage-sensitive Ca channels in nerve endings may be one mechanism controlling transmitter release.

Animals↗
PubMed1984

Effect of 2450 MHz microwave energy on the blood-brain barrier to hydrophilic molecules. A. Effect on the permeability to sodium fluorescein.

Significantly elevated levels of sodium fluorescein (MW 376) were found only in the brains of conscious rats made considerably hyperthermic (colonic temperatures greater than 41.0 degrees C) by exposure to ambient heat (42 +/- 2 degrees C) for 90 min or 2450 MHz CW microwave energy at 65 mW/cm2 (SAR approximately equal to 13.0 W/kg) for 30 or 90 min. For microwave-exposed rats, fluorescein levels within the cortex and hypothalamus appeared to increase with increasing duration of exposure. This trend was not apparent in the cerebellum or medulla. Exposure to ambient heat resulted in increased fluorescein with the cortex, hypothalamus and medulla, but not the cerebellum, and, in general, ambient heat was not as effective as microwave energy in raising tracer concentrations within the brain. By far the greatest elevation of fluorescein dye in the brain occurred in those animals whose blood-brain barrier had been opened osmotically by intracarotid injection of 10 M urea. It is suggested that increased levels of sodium fluorescein found in the brain tissue of ambient heat and microwave-exposed rats most likely represent technically derived artifact and not a breakdown of the blood-brain barrier.

Animals↗
PubMed1984

Opiates stimulate low Km GTPase in brain.

Low Km GTP hydrolysis in rat brain is stimulated in a concentration-dependent manner by the opiate alkaloid etorphine, and by the opioid peptide D-Ala2-leucine-enkephalinamide. The opiate antagonist naloxone inhibits the maximal D-Ala2-leucine-enkephalinamide stimulation of the GTPase, also with concentration dependency. The magnitude of maximally stimulated, opioid-sensitive, GTP hydrolysis is differentially distributed across brain regions. Opioid-stimulated GTPase may represent one means of identifying a specific type of opioid receptor.

Adenylyl Cyclase Inhibitors↗
PubMed1984

Depolarization-induced increase in synaptosomal membrane calcium monitored by chlorotetracycline fluorescence.

Chlorotetracycline (CT) was used as a fluorescent probe for membrane calcium with intact synaptosomes. The net increase in fluorescence intensity at 520 nm, which is a measure of membrane-bound Ca, increases with increasing Ca, saturating in the millimolar range. Membrane Ca can also be detected in the absence of added external Ca. Potassium-induced depolarization of synaptosomes leads to an increase in membrane Ca, reaching a new steady-state value within 5 min. Neither opiates nor phenytoin affected synaptosomal membrane Ca. Relatively high concentrations of chlorotetracycline increased depolarization-induced uptake of 45Ca into synaptosomes. The data suggest that the Ca-CT complex binds to synaptic plasma membranes, and that depolarization-induced Ca influx results in increased Ca binding to the internal surface of the plasma membrane and/or other internal membranes.

Animals↗
PubMed1983

Effects of opiates on synaptosomal calmodulin and calcium uptake.

Acute opiate administration in vivo increases the level of cytoplasmic calmodulin in isolated rat brain synaptosomes. These synaptosomes do not, however, display decreased K+-stimulated 45Ca uptake in vitro. Opiates affect neither cytoplasmic calmodulin nor Ca uptake after incubation of synaptosomes with the drugs in vitro. In contrast to the interpretation of electrophysiological data, these results suggest that the observed inhibition by opiates of the release of several transmitters may not be mediated by presynaptic opiate receptors that inhibit Ca uptake.

Animals↗
PubMed1983

Activation of fluoride-stimulated adenylate cyclase by phospholipase A2 in the caudate nucleus of the rat brain.

Phospholipase A2 (PLA2) increases adenylate cyclase (AC) activity in the rat caudate nucleus in a dose-dependent manner. After maximal stimulation by fluoride, PLA2 treatment further increases AC activity 2.4 fold. Adenylate cyclase activity is maximal after 45% hydrolysis of the phospholipids. Of the products of PLA2 treatment only lysophosphatidylcholine (LPC) produces such an increase in AC activity. In contrast to PLA2 treatment, LPC solubilizes the enzyme, decreases the Km value for ATP, and requires much larger amounts of LPC than that produced by lipase treatment. After maximal stimulation with fluoride and PLA2, removal of most of the LPC does not reduce the activity of adenylate cyclase. These findings suggest that removal of membrane lipid rather than generation of LPC is responsible for the activation of brain adenylate cyclase by phospholipase A2.

Adenylyl Cyclases↗