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Biomedical subjects

J Geiger

Publications and source records attributed to J Geiger.

At least 37 records · Page 2Linked to original sources
PubMed1999

Flow cytometry analysis of intracellular VASP phosphorylation for the assessment of activating and inhibitory signal transduction pathways in human platelets--definition and detection of ticlopidine/clopidogrel effects.

Increased platelet adhesion or aggregation are key events in the pathogenesis of cardiovascular diseases. Exact determination of the platelet activation state is essential to recognize, prevent, and treat cardiovascular complications due to platelet dysfunction. Initial phases of platelet activation and inhibition are characterized by phosphorylation of specific intracellular proteins. However, methodological problems often prevent analysis of platelet protein phosphorylation under clinical conditions. A novel flow cytometry-based method using a phosphorylation-specific antibody was developed for fast and easy quantification of the phosphorylation state of a specific intracellular platelet protein. This method was used to analyze various platelet receptors and their intracellular signaling which may be impaired in genetic or acquired disorders or altered due to therapeutic interventions. In a first clinical application, the inhibitory effects of ticlopidine and clopidogrel on the platelet P2YAC ADP receptor were monitored.

Adult↗
PubMed1998

Ligand specificity and ticlopidine effects distinguish three human platelet ADP receptors.

Human platelets express adenosine 5'-diphosphate (ADP)-specific purinoceptors of the P2X and P2Y receptor superfamily, but their structure, diversity, and precise pharmacological profile is not well understood. Here, functional assays with intact platelets and well-characterized nucleotide derivatives were performed in order to characterize the ligand specificity of these platelet-specific purinoceptors. For the signalling pathways investigated (aggregation, rapid Ca2+-influx, desensitization of Ca2+-influx, Ca2+-mobilization, inhibition of adenylyl cyclase), significant differences in ligand specificity were demonstrated. ADP activated all purinoceptors of human platelets, while adenosine 5'-triphosphate (ATP) was a weak agonist for the P2X receptor and an antagonist for the P2Y receptors. The ADP-receptor pathway-antagonist ticlopidine inhibited ADP-evoked aggregation and adenylyl cyclase inhibition but did not affect platelet purinoceptors associated with Ca2+-influx and Ca2+-mobilization. These results indicate the presence of three distinct ADP-selective purinoceptors on human platelets.

Adenosine Diphosphate↗
PubMed1998

Outpatient pediatric orthopedics. Common and important conditions.

Many common pediatric orthopedic conditions can be managed by the pediatrician who has a knowledge of the natural history of these conditions. An accurate diagnosis is necessary to provide proper treatment, give advice to patients, or make referrals to the proper specialist. The authors' find that in approximately 95% of cases, a specific diagnosis can be made and that 40% of patient referrals for orthopedic problems could have been managed by the primary care physician. This article discusses some of the more common pediatric orthopedic problems often encountered by primary care physicians.

Adolescent↗
PubMed1998

Neurobiological aspects of human immunodeficiency virus infection: neurotoxic mechanisms.

Dementia due to human immunodeficiency virus (HIV) infection is the commonest cause of dementia in children, young adults and middle-aged people. Its incidence continues to rise despite the use of newer antiretroviral agents. The study of the pathogenesis of HIV dementia has lead to the discovery of novel mechanisms of neural dysfunction and toxicity, and holds promise for further discovery of new molecules and pathways involved in maintaining cerebral function and enabling dysfunction. New to the field of neurovirology is the emerging concept that proteins that are part of the virus may themselves be neurotoxic by virtue of their abilities to be either directly toxic to brain cells or may, through their actions on glial cells or macrophages, release neurotoxic products coded by the host genome. These mechanisms have been demonstrated for HIV-1 and accordingly we propose a new term, virotoxins, to describe such actions. This review provides an in-depth analysis of the pathophysiological mechanisms by which these viral and cellular products affected by HIV virotoxins cause neural dysfunction.

HIV Infections↗
PubMed1997

Functional properties of AMPA and NMDA receptors expressed in identified types of basal ganglia neurons.

AMPA- and NMDA-type glutamate receptors (AMPARs and NMDARs) mediate excitatory synaptic transmission in the basal ganglia and may contribute to excitotoxic injury. We investigated the functional properties of AMPARs and NMDARs expressed by six main types of basal ganglia neurons in acute rat brain slices (principal neurons and cholinergic interneurons of striatum, GABAergic and dopaminergic neurons of substantia nigra, globus pallidus neurons, and subthalamic nucleus neurons) using fast application of glutamate to nucleated and outside-out membrane patches. AMPARs in different types of basal ganglia neurons were functionally distinct. Those expressed in striatal principal neurons exhibited the slowest gating (desensitization time constant tau = 11.5 msec, 1 mM glutamate, 22 degrees C), whereas those in striatal cholinergic interneurons showed the fastest gating (desensitization time constant tau = 3.6 msec). The lowest Ca2+ permeability of AMPARs was observed in nigral dopaminergic neurons (PCa/PNa = 0.10), whereas the highest Ca2+ permeability was found in subthalamic nucleus neurons (PCa/PNa = 1.17). NMDARs of different types of basal ganglia neurons were less variable in their functional properties; those expressed in nigral dopaminergic neurons exhibited the slowest gating (deactivation time constant of predominant fast component tau1 = 150 msec, 100 microM glutamate), and those of globus pallidus neurons showed the fastest gating (tau1 = 67 msec). The Mg2+ block of NMDARs was similar; the average chord conductance ratio g-60mV/g+40mV was 0.18-0.22 in 100 microM external Mg2+. Hence, AMPARs expressed in different types of basal ganglia neurons are markedly diverse, whereas NMDARs are less variable in functional properties that are relevant for excitatory synaptic transmission and neuronal vulnerability.

Animals↗
PubMed1995

Platelet-vessel wall interactions, focal adhesions, and the mechanism of action of endothelial factors.

Endothelial cells produce a variety of vasoactive substances including prostacyclin (PGI2) and endothelium-derived relaxing factor (EDRF/NO) which are potent inhibitors of platelet adhesion/aggregation and vascular smooth muscle cell contraction/proliferation. PGI2 and EDRF elevate cAMP or cGMP, respectively, in vascular cells and other targets. The intracellular effects of cAMP and cGMP in vascular smooth muscle cells and platelets are primarily mediated by the family of cAMP- and cGMP-dependent protein kinases and their substrates. Important effector systems include enzymes, channels and regulatory proteins responsible for the regulation of intracellular Ca++. Other evidence suggests that VASP, a focal adhesion protein phosphorylated in platelets and smooth muscle cells in response to PGI2 and EDRF, is important for the regulation of integrins and cell-matrix interactions.

Blood Platelets↗
PubMed1994

Regulation of calcium mobilization and entry in human platelets by endothelium-derived factors.

Stimulation of Ca2+ mobilization and entry by agonists such as ADP, thrombin, and thromboxane is an early step of platelet activation. Here, we compared the effects of adenosine 3',5'-cyclic monophosphate (cAMP)-elevating prostaglandins, guanosine 3',5'-cyclic monophosphate (cGMP)-elevating nitrovasodilators, membrane-permeant selective activators of cAMP- or cGMP-dependent protein kinases, and physiological endothelium-derived factors on the agonist-evoked Ca2+ mobilization and entry in human platelets. Prostaglandin E1, the prostacyclin analogue Iloprost, the nitric oxide (NO) donor 3-morpholinosydnonimine hydrochloride, and selective activators of cGMP- or cAMP-dependent protein kinase strongly inhibited the agonist-evoked Ca2+ mobilization from intracellular stores and associated late Ca2+ entry but had little effects on the rapid (1st) phase of ADP-evoked Ca2+ entry. During coincubation of platelets with endothelial cells, endothelium-derived factors that were released strongly inhibited platelet agonist-evoked Ca2+ mobilization and only moderately affected the rapid phase of ADP-evoked Ca2+ entry. These effects were partially prevented when endothelial cells were preincubated with cyclooxygenase and/or NO synthase inhibitors. Endothelial cells therefore produce sufficient quantities of labile platelet inhibitors whose effects on the platelet Ca2+ response resemble those observed with selective cAMP- and cGMP-dependent protein kinase activators.

Biological Transport↗
PubMed1994

Human cyclic GMP-dependent protein kinase I beta overexpression increases phosphorylation of an endogenous focal contact-associated vasodilator-stimulated phosphoprotein without altering the thrombin-evoked calcium response.

The role of the cGMP-dependent protein kinase (cGK) and one of its major substrates, the vasodilator-stimulated phosphoprotein (VASP), in the regulation of a receptor-evoked calcium response was investigated. The human type I beta cGK was stably transfected in human embryonic kidney 293 cells and Swiss mouse 3T6 fibroblasts, which contained significant or no detectable levels of the focal adhesion protein VASP, respectively. Western blot analysis and protein kinase activity measurements demonstrated an 8-fold overexpression of cGK-I beta in 293 cells (7-fold in 3T6 cells), representing an intracellular cGK concentration of 0.33 microM. In experiments with intact 293 cells expressing cGK-I beta, beta-phenyl-1,N2-etheno-cGMP and 8-(p-chlorophenylthio)-cGMP were capable of converting up to 30-40% of the 46-kDa VASP to its 50-kDa phospho- form, equivalent to results observed with cGMP analogs that cause a marked inhibition of the stimulated Ca2+ transient in intact human platelets. In contrast to platelets, preincubation of fura-2-loaded 293 and 3T6 cells with 8-(p-chlorophenylthio)-cGMP did not significantly inhibit thrombin-evoked calcium transients, although sufficient cGK-mediated VASP phosphorylation was clearly detectable under these conditions in cGK-I beta-expressing 293 cells. These results demonstrate that cGK inhibition of agonist-evoked calcium mobilization is not a mechanism common to all cell types and that VASP phosphorylation may not be an essential or sufficient component of the cGK effect on calcium levels. In contrast, the observed VASP phosphorylation mediated by recombinant human cGK-I beta in intact 293 cells does support the hypothesis that focal adhesions and their associated proteins are important cellular sites of cGK action.

Blood Proteins↗
PubMed1993

Defective nitrovasodilator-stimulated protein phosphorylation and calcium regulation in cGMP-dependent protein kinase-deficient human platelets of chronic myelocytic leukemia.

The presence and functional role of the cyclic nucleotide signal transduction system was investigated in platelets from patients with myeloproliferative disorders. Platelets from certain patients with chronic myelocytic leukemia showed decreased expression of cGMP-dependent protein kinase, and platelets from two such patients were studied in some detail. These platelets had very little if any cGMP-dependent protein kinase but a normal level of cAMP-dependent protein kinase. They also contained a normal level of VASP (vasodilator-stimulated phosphoprotein, a specific substrate of both cAMP- and cGMP-dependent protein kinase), as well as a functionally intact prostaglandin E1-stimulated cAMP-mediated VASP phosphorylation. In contrast, sodium nitroprusside-stimulated VASP phosphorylation was severely impaired in these cGMP-dependent protein kinase-deficient platelets, despite an exaggerated cGMP response to sodium nitroprusside. Furthermore, whereas selective activation of the cGMP-dependent protein kinase by 8-(4-chlorophenylthio)-cGMP strongly inhibited the ADP- or thrombin-evoked calcium mobilization from intracellular stores in normal platelets, this agonist-evoked calcium response was not inhibited by the cGMP analog in cGMP-dependent protein kinase-deficient platelets. The results demonstrate a defect in the nitrovasodilator-/cGMP-regulated signal transduction system in human platelets from some patients with myeloproliferative disorders, and underscore that a cGMP-dependent protein kinase regulatory system, distinct from that of cAMP-dependent protein kinase or other cGMP-dependent effectors is operative in normal human platelets.

Blood Platelets↗
PubMed1993

Role of cyclic nucleotide-dependent protein kinases and their common substrate VASP in the regulation of human platelets.

The activation of human platelets is inhibited by two intracellular pathways regulated by either cGMP- or cAMP-elevating agents. There is considerable evidence that the inhibitory effects of cGMP and cAMP are mediated by the cGMP-PK and cAMP-PK, respectively, in human platelets. The cGI-PDE is an additional target for cGMP, and the cGMP-mediated elevation of cAMP levels contributes to the well known synergism between cAMP- and cGMP-elevating platelet inhibitors. Stimulation of both cAMP-PK and cGMP-PK prevents the agonist-induced activation of MLCK and PKC and inhibits the agonist-induced calcium mobilization from intracellular stores without any major effect on the ADP-regulated cation channel. These studies suggest that the inhibition of an early event of platelet activation, e.g. activation of PLC, is an effect common to both cGMP-PK and cAMP-PK stimulation. A common substrate of both cGMP-PK and cAMP-PK, the 46/50 kDa protein VASP, has been recently identified as a novel microfilament- and focal contact-associated protein whose phosphorylation correlates very well with platelet inhibition. Future investigations will have to identify the precise molecular mechanism of cyclic nucleotide inhibition of Ca2+ discharge from intracellular stores and whether cGMP-PK- and cAMP-PK-mediated VASP phosphorylation is an important component of this effect of cyclic nucleotides in human platelets.

Adenylyl Cyclases↗
PubMed1993

Properties and regulation of human platelet cation channels.

The stimulation of calcium influx by various human platelet agonists which differ in their activation pathways was investigated. ADP activates a receptor-operated cation channel (ROC) and stimulates a phospholipase C (PLC)/inositol-trisphosphate (IP3)-mediated calcium mobilization associated with a secondary calcium influx. Thrombin only stimulates the PLC/IP3-mediated calcium mobilization and associated calcium influx, perhaps followed by an additional phase of calcium influx. The platelet calcium response after incubation with the thromboxane A2 mimetic U 46619 is similar but more transient compared to that after thrombin stimulation. Tert-butylhydroquinone (an inhibitor of endoplasmatic reticulum Ca(2+)-ATPases and cyclooxygenase) elevates cytosolic calcium levels by emptying intracellular calcium stores and stimulates a biphasic calcium influx. Activation of platelet cAMP- and cGMP-dependent protein kinases inhibits the ADP- and thrombin-evoked, calcium store-associated cation influx, but not the fast receptor operated cation influx induced by ADP. Experiments with various ADP-analogs, ATP and ATP-gamma-S suggest that two different ADP-receptors may mediate the calcium responses in human platelets.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1993

[Malignant thyroid tumor surgery at the Surgery Clinic of the Medical School Hospital in Pilsen 1987-1991].

At the surgical clinic of the Faculty Hospital in Plzen in 1987-1991 a total of 230 operations of the thyroid gland were performed in 227 patients, incl., 30 operations on account of malignancies in 27 patients. The presented study is focused on malignant diseases. The mean age of the patients was 57.7 years, women predominated. Postoperative complications such as pareses of the recurrent nerve occurred only in one patient. Only one patient died from generalization of thyroid carcinoma. The authors compared the group with a previous clinical study made in 1967-1983 and with the year 1992. In 1992 they proved an increase of benign and malignant thyroid disease.

Adolescent↗
PubMed1992

Role of cGMP and cGMP-dependent protein kinase in nitrovasodilator inhibition of agonist-evoked calcium elevation in human platelets.

Most platelet agonists activate and elevate the cytosolic free calcium concentration in human platelets through receptor-dependent mechanisms that are antagonized by cAMP- and cGMP-elevating agents. Nitrovasodilators such as nitroprusside and endothelium-derived relaxing factor are potent cGMP-elevating platelet inhibitors. In the present study, the role of cGMP and cGMP-dependent protein kinase in nitrovasodilator inhibition of ADP- and thrombin-evoked calcium elevation and activation of human platelets was investigated. Preincubation of platelets with 8-(4-chlorophenylthio)guanosine 3',5'-cyclic monophosphate (8-pCPT-cGMP; a membrane-permeant selective activator of the cGMP-dependent protein kinase that does not significantly affect cGMP-regulated phosphodiesterases) inhibited the thrombin-induced phosphorylation mediated by myosin light chain kinase and protein kinase C. Nitrovasodilator-induced protein phosphorylation in human platelets was distinct from that induced by cAMP-elevating prostaglandins and could be mimicked by 8-pCPT-cGMP. Preincubation of human platelets with nitrovasodilators or 8-pCPT-cGMP inhibited the ADP- and thrombin-evoked calcium elevation in the presence and absence of external calcium. Nitrovasodilators and 8-pCPT-cGMP also inhibited the agonist-induced Mn2+ influx, but stopped-flow experiments indicated that the ADP receptor-operated cation channel was not significantly inhibited. These results suggest that in human platelets nitrovasodilators inhibit the agonist-induced calcium mobilization from intracellular stores and the secondary store-related calcium influx but not the ADP receptor-operated cation channel. The results also suggest that these nitrovasodilator effects are mediated by cGMP and the cGMP-dependent protein kinase.

Adenosine Diphosphate↗
PubMed1992

[The effect increased choline levels on the synthesis and release of acetylcholine in heart atria in white rats].

The paper addresses the problem of (1) the relationship of choline in extracellular fluid and acetylcholine (ACh) synthesis in chambers of the heart of white rats, and (2) the possibility of physiological involvement of this ACh in the control of cardiac activity. Within 60 min after s.c. administration of choline in the dose of 300 mg/kg body weight the ACh content rose to 136% of the control value in isolated heart chambers and after administration of 400 mg/kg body weight to 159% of the control value. Increased ACh synthesis failed to affect the heart rate, nor did it increase the tonic effect of vagus innervation of the heart. Excessive ACh could however be released by electric transmural stimulation of isolated heart chambers as well as by potassium depolarization. The release depended on the presence of calcium ions. The obtained results demonstrate that an increase in the level of choline in extracellular fluid results in increased ACh synthesis in nerve terminals. Enhanced release of this ACh is a precondition for high choline levels to induce an increase in parasympathetic control of cardiac function.

Acetylcholine↗
PubMed1991

Substance P-like immunoreactivity and somatostatin-like immunoreactivity in the ventricular fluid of patients with chronic pain syndromes.

Substance P-like and somatostatin-like immunoreactivities (SPLI and SLI) were determined in ventricular fluid of patients with chronic pain syndromes and in a comparison group with multiple sclerosis, essential tremor, epilepsy and postanoxic myoclonus. Concentrations of SPLI and SLI were non-significantly decreased by 40% and 33% in chronic pain patients as compared with control patients without pain. There were no differences apparent between subgroups of pain patients (deafferentation pain, neoplasia-induced pain, thalamic pain). High pressure liquid chromatography combined with radioimmunoassay showed marked heterogeneity of SPLI and SLI.

Adult↗
PubMed1991

Ventricular fluid neuropeptides in Parkinson's disease. II. Levels of substance P-like immunoreactivity.

Substance P-like immunoreactivity (SPLI) was determined in cerebrovascular fluid of patients with extrapyramidal motor diseases. Patients with Parkinson's disease (PD) showed a SPLI concentration decreased by 30% compared with patients without extrapyramidal disease. No differences were apparent for patients with dystonia. Fluid obtained from the foramen Monro showed higher SPLI concentrations than fluid from a lateral ventricle, indicating that hypothalamic sources are important for ventricular substance P. Lateral ventricular SPLI was particularly low in parkinsonian patients which raises the possibility of a decreased SPergic activity in basal ganglia occurring in PD.

Adult↗