Search PubMed⌕ Search

Biomedical subjects

J Horak

Publications and source records attributed to J Horak.

At least 19 recordsLinked to original sources
PubMed2001

Optimisation of the quantitative determination of chlormequat by matrix-assisted laser desorption/ionisation mass spectrometry.

The plant growth regulator chlormequat, an involatile quaternary ammonium salt, has been quantified by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOFMS). Restrictions for quantitative MALDI-TOFMS analysis, such as irreproducible crystallisation and unsatisfactory laser stability, have been overcome by the application of two synthesised isotopically labelled standards and the optimisation of the measurement protocol. Data acquisition at constant laser power was compared to data acquisition at approximately constant ion abundance of the relevant ions (analyte and internal standards). Data acquisition at constant ion abundance performed better and enabled a high number of consecutive firings to the same sample deposition area. Furthermore an increased sample-to-sample repeatability and a high reproducibility over several weeks without re-calibration have been attained by this method. Linearity over three orders of magnitude (0.05 to 30 ng/microL chlormequat), with a correlation coefficient of 0.9997, was achieved using [13C3]-chlormequat as internal standard. Limit of detection and limit of determination were determined to be in the low pg/microL range for pure standard solutions. Thin-layer chromatography was applied for the removal of high amounts of choline, which is often present in plant tissue extracts and can adversely affect the ionisation and detection of chlormequat by MALDI-TOFMS. The use of two internal standards ([13C3]- and [2H9]-chlormequat) enabled direct quantification and simultaneous control of the recovery.

Calibration↗
PubMed2001

Virtual PCR.

UNLABELLED: We present an algorithm that uses public sequence data to predict PCR products. The algorithm is implemented as a CGI script. Output is compared to real-world PCR. AVAILABILITY: Perl code and instructions for installation are freely available over the internet at http://www.sci.muni.cz/LMFR/vpcr.html.

Algorithms↗
PubMed2001

Glucose-induced monoubiquitination of the Saccharomyces cerevisiae galactose transporter is sufficient to signal its internalization.

In Saccharomyces cerevisiae, the addition of glucose to cells growing on galactose induces internalization of the galactose transporter Gal2p and its subsequent proteolysis in the vacuole. Here we report that the essential step in Gal2p down-regulation is its ubiquitination through the Ubc1p-Ubc4p-Ubc5p triad of ubiquitin-conjugating enzymes and Npi1/Rsp5p ubiquitin-protein ligase. Moreover, Gal2p appears to be stabilized in mutant cells defective in the ubiquitin-hydrolase Npi2p/Doa4p, and the mutant phenotype can be reversed by overexpression of ubiquitin. An analysis of the fate of Gal2p in cells overexpressing wild-type ubiquitin as well as its variants incompetent to form polyubiquitin chains showed that monoubiquitination of Gal2p is sufficient to signal internalization of the protein into the endocytic pathway.

Endosomal Sorting Complexes Required for Transport↗
PubMed2000

Emergent management of the airway. New pharmacology and the control of comorbidities in cardiac disease, ischemia, and valvular heart disease.

Once it is decided that the patient in distress requires tracheal intubation, the primary goal is to secure the airway as quickly and safely as possible to assure adequate oxygenation and ventilation. The clinician should quickly review the patient's history, physical examination findings, and laboratory data to determine the presence of cardiovascular disease, assess intravascular volume status, and formulate a plan for induction of anesthesia. The stresses of hypoxia, hypercarbia, acidosis, and extreme fatigue result in near-maximal sympathetic outflow that is manifest as tachycardia, labile blood pressure, and increased myocardial contractility. The astute clinician should anticipate that the tachycardia and hypertension associated with laryngoscopy and tracheal intubation is followed by a period of hypotension. This postintubation hypotension results from the acute marked attenuation of the sympathetic tone associated with resolution of hypoxia and hypercarbia, direct drug-induced negative inotropic effect, and vasodilation. The decrease in sympathetic vascular tone may result in hypotension by exacerbating the decrease in cardiac preload and afterload from hypovolemia. In addition, the use of positive pressure ventilation and positive end-expiratory pressure (PEEP) in these hypovolemic patients will further decrease ventricular preload by impeding venous return, leading to profound hypotension. Several pharmacologic agents are required to treat effectively the hemodynamic perturbations associated with induction, laryngoscopy, and tracheal intubation. Most sedative hypnotic agents that are administered for induction provide minimal to no analgesia. Patients are most often given a combination of drugs to provide adequate sedation, analgesia to blunt the noxious stimuli, and muscle relaxation to facilitate the laryngoscopy. The major challenge is to choose a combination of drugs that at the appropriate doses, effectively blunt the responses to intubation without contributing to postlaryngoscopy hypotension. One can use several strategies to accomplish these goals; administration of a narcotic analgesic before induction decreases the dose of induction agent and can attenuate the sympathetic response to intubation. Because of the prevalence of cardiovascular disease and hypovolemia in this population of patients, all chosen drugs should have minimal negative effect on cardiac function and patients with hypovolemia should be hydrated. Most clinical studies have been performed in hemodynamically stable patients, so the routine dosages of sedative hypnotics should be reduced substantially and titrated to effect. An additional strategy is to treat significant hemodynamic perturbations with vasopressors, vasodilators, short-acting selective beta-1 blockers, and inotropic agents. The choice of vasoactive agent depends on the magnitude of the hemodynamic response and the presence of specific underlying cardiovascular pathology.

Airway Obstruction↗
PubMed1998

The pharmacokinetics of lamivudine in patients with impaired hepatic function.

OBJECTIVE: This study was designed to evaluate the effect of hepatic impairment on the pharmacokinetics of lamivudine. METHODS: Sixteen patients not infected with hepatitis B virus or human immunodeficiency virus who had hepatic impairment due to liver cirrhosis were assigned to moderately or severely impaired groups by clinical signs/symptoms, 14C-aminopyrine metabolic activity and caffeine clearance and compared with eight healthy controls. Following a 300-mg dose of lamivudine, blood and urine samples were taken for drug assay. RESULTS: Lamivudine was well tolerated in patients with hepatic impairment. There were no statistical differences in overall lamivudine exposure (in terms of AUC or Cmax) or other major pharmacokinetic parameters i.e. CLR, tmax and t1/2, between healthy control subjects and patients with moderate or severe hepatic impairment. CONCLUSIONS: Hepatic impairment does not warrant dose modification of lamivudine based on this single-dose pharmacokinetic study.

Adult↗
PubMed1998

Coronary angiography in Qatar: the first ten years.

Cardiac catheterization in Qatar was initiated in July 1982. In ten years, a total of 3900 procedures were performed at Hamad General Hospital. Computerized data registry has been maintained since 1982. Isolated coronary angiography was done in 2911 patients; of these, 2635 (90.5%) were men, and 276 (9.5%) were women, the average age of the patients was 47+/-9.2 years (range, twenty-five to eighty-eight). Patients' nationality was Qatari in 492 (17%), and other Arabs in 610 (21%), and 1512 (52%) were from the Asian subcontinent. Myocardial infarction was the most common indication (43%). Single-vessel disease was found in 638 (22%), two-vessel disease in 630 (22%), three-vessel disease in 950 (33%), and nonsignificant coronary artery disease in 693 (24%) patients. Morbidity related to the coronary angiography was reported in 147 (5%) patients, but there was no mortality related to the procedure. In 822 (28%) patients, the age was forty years or younger. The angiographic findings of these younger patients were compared with those of the older ones. Younger patients were usually men of Asian subcontinental origin with a recent myocardial infarction (MI). Often, they had normal coronary arteries or single-vessel disease. Patients of Asian subcontinent origin were usually young male patients with a recent MI, who receive streptokinase, and have single-vessel disease.

Adult↗
PubMed1997

Catabolite inactivation of the galactose transporter in the yeast Saccharomyces cerevisiae: ubiquitination, endocytosis, and degradation in the vacuole.

When Saccharomyces cerevisiae cells growing on galactose are transferred onto glucose medium containing cycloheximide, an inhibitor of protein synthesis, a rapid reduction of Gal2p-mediated galactose uptake is observed. We show that glucose-induced inactivation of Gal2p is due to its degradation. Stabilization of Gal2p in pra1 mutant cells devoid of vacuolar proteinase activity is observed. Subcellular fractionation and indirect immunofluorescence showed that the Gal2 transporter accumulates in the vacuole of the mutant cells, directly demonstrating that its degradation requires vacuolar proteolysis. In contrast, Gal2p degradation is proteasome independent since its half-life is unaffected in pre1-1 pre2-2, cim3-1, and cim5-1 mutants defective in several subunits of the protease complex. In addition, vacuolar delivery of Gal2p was shown to be blocked in conditional end3 and end4 mutants at the nonpermissive temperature, indicating that delivery of Gal2p to the vacuole occurs via the endocytic pathway. Taken together, the results presented here demonstrate that glucose-induced proteolysis of Gal2p is dependent on endocytosis and vacuolar proteolysis and is independent of the functional proteasome. Moreover, we show that Gal2p is ubiquitinated under conditions of glucose-induced inactivation.

Azides↗
PubMed1994

Progression of venoconstriction in patients after heart transplantation during exercise.

Changes of both central hemodynamics and peripheral circulation in non-exercising muscle were investigated in 17 patients after successful orthotopic heart transplantation during moderate supine isotonic leg-exercise. Changes of peripheral circulation were measured in 14 healthy controls. The cardiac output rose from 5.71 to 9.45 l/min, the right atrial pressure from 3.5 to 12 mmHg, mean pulmonary arterial pressure from 17.4 to 36.9 mmHg, and pulmonary capillary wedger pressure from 9.5 to 23.5 mmHg. Venoconstriction, already present in the rest in patients after heart transplantation, further increased during the exercise (venous compliance lowered from 0.0454 to 0.0309 ml/mmHg). In controls no changes were observed (venous compliance being 0.0833 at rest and 0.0839 ml/mmHg during exercise). Negative correlation was found between an increase in pulmonary arterial pressure and a decrease in venous compliance. The authors hypothesise that venoconstriction could serve to increase of cardiac output via Frank-Starling mechanisms in patients after heart transplantation. Forearm blood flow during the exercise decreased (from 3.4 to 2.0 ml/100 ml/min), while local peripheral resistance rose (from 35.9 to 78.8 units) in patients after heart transplantation. These changes were not observed in controls.

Adult↗
PubMed1991

Saccharomyces cerevisiae null mutants in glucose phosphorylation: metabolism and invertase expression.

A congenic series of Saccharomyces cerevisiae strains has been constructed which carry, in all combinations, null mutations in the three genes for glucose phosphorylation: HXK1, HXK2 and GLK1, coding hexokinase 1 (also called PI or A), hexokinase 2 (PII or B), and glucokinase, respectively: i.e., eight strains, all of which grow on glucose except for the triple mutant. All or several of the strains were characterized in their steady state batch growth with 0.2% or 2% glucose, in aerobic as well as respiration-inhibited conditions, with respect to growth rate, yield, and ethanol formation. Glucose flux values were generally similar for different strains and conditions, provided they contained either hexokinase 1 or hexokinase 2. And their aerobic growth, as known for wild type, was largely fermentative with ca. 1.5 mol ethanol made per mol glucose used. The strain lacking both hexokinases and containing glucokinase was an exception in having reduced flux, a result fitting with its maximal rate of glucose phosphorylation in vitro. Aerobic growth of even the latter strain was largely fermentative (ca. 1 mol ethanol per mol glucose). Invertase expression was determined for a variety of media. All strains with HXK2 showed repression in growth on glucose and the others did not. Derepression in the wild-type strain occurred at ca. 1 mM glucose. The metabolic data do not support- or disprove-a model with HXK2 having only a secondary role in catabolite repression related to more rapid metabolism.

Gene Expression Regulation, Fungal↗
PubMed1986

Central antiarrhythmic effects of imidazole in anesthetized rats.

In urethane anesthetized rats, the intracerebroventricular (icv.) microinjection of sodium glutamate or KCl induced cardiac arrhythmias. These cardiac rhythm disorders could be prevented by the icv. administration of imidazole. The i.v. injection of the same doses of imidazole elicited cardiac arrhythmias. The antiarrhythmic activity of imidazole is probably due to its ability to stimulate phosphodiesterase activity, which leads to a decrease in cGMP and/or cAMP cerebral levels.

Anesthesia↗
PubMed1986

Central antiarrhythmic activity of adenosine in anesthetized rats.

In urethane-anesthetized rats the intracerebroventricular (icv.) administration of sodium glutamate or desipramine induced cardiac arrhythmias. These cardiac rhythm disturbances could be prevented by icv. administration of adenosine. The i.v. injection of adenosine had an arrhythmogenic action. The antiarrhythmic effect of adenosine could be reversed by icv. aminophylline. It is suggested that the antiarrhythmic activity of adenosine is due to the central inhibition of release of acetylcholine, and/or noradrenalin, produced by the decreased availability of calcium for the excitation-secretion coupling.

Adenosine↗
PubMed1979

Evaluation of a new cardiotomy blood filter.

A new cardiotomy blood filter with a polycarbonate body, a polyester prefilter, and a nylon screen with 20 mu pores was compared with four other commercially available filters. The Optigard filter was found to function as a "surface filter," which effectively removes blood particles larger than its nominal pore size.

Cardiopulmonary Bypass↗