Search PubMed⌕ Search

Biomedical subjects

J Holtz

Publications and source records attributed to J Holtz.

At least 55 records · Page 3Linked to original sources
PubMed1998

Mechanism of ET(A)-receptor stimulation-induced increases in intracellular Ca2+ in SK-N-MC cells.

The mechanism underlying endothelin-1 (ET-1)-induced increases in intracellular Ca2+ concentrations in the human neuroblastoma cell-line SK-N-MC was investigated. ET-receptor agonists increased inositol phosphate (IP)-formation (assessed as accumulation of total [3H]-IPs in [3H]-myo-inositol prelabelled cells) and intracellular Ca2+ (assessed by the FURA-2 method) with an order of potency: ET-1 > sarafotoxin 6b (S6b)> ET-3 = S6c; the ETA-receptor antagonist BQ-123 inhibited both responses with apparent pKi-values of 8.3 and 8.6, respectively, while the ETB-receptor antagonist BQ-788 did not. Pretreatment of the cells with pertussis toxin (PTX, 500 ng ml(-1) overnight) reduced ET-1-induced Ca2+ increases by 46+/-5%, but rather enhanced ET-1-induced IP-formation. Chelation of extracellular Ca2+ by 5 mM EGTA did not affect ET-1-induced IP-formation. However, in the presence of 5 mM EGTA or SKF 96365, an inhibitor of receptor mediated Ca2+ influx (1.0-3.0 x 10(-5) M) ET-1-induced Ca2+ increases were inhibited in normal, but not in PTX-treated cells. [125I]-ET-1 binding studies as well as mRNA expression studies (by RT-PCR) detected only ETA-receptors whereas expression of ETB-receptor mRNA was marginal. ET-1 (10(-8) M) inhibited isoprenaline-evoked cyclic AMP increases; this was antagonized by BQ-123, not affected by BQ-788 and abolished by PTX-treatment. We conclude that SK-N-MC cells contain a homogeneous population of ETA-receptors that couple to IP-formation and inhibition of cyclic AMP formation. Stimulation of these ETA-receptors increases intracellular Ca2+ by at least two mechanisms: a PTX-insensitive IP-mediated Ca2+ mobilization from intracellular stores and a PTX-sensitive influx of extracellular Ca2+.

Adrenergic beta-Agonists↗
PubMed1998

Hand-arm vibration syndrome with proximal ulnar artery occlusion.

The case of a man exposed during 25 years to vibration while maneuvering a heavy earth moving tractor is reported. The first clinical manifestation of hand-arm vibration syndrome was a bilateral Raynaud's phenomenon followed five years later by digital necrosis. The arteriography revealed a proximal and bilateral ulnar artery occlusion. Bilateral median nerve conduction abnormalities were also present. Vibration exposure level was much higher than the threshold level proposed by the European Commission. Laboratory examinations for vasculitis and other vascular diseases were all negative. The purpose of this report is to show that vibration can be responsible for proximal occlusion of a medium sized artery and severe neurovascular abnormalities which must be distinguished from the usual vasospastic Raynaud's phenomenon and the classical hypothenar hammer syndrome. An early and correct diagnosis is crucial because continued repetitive trauma can result in irreversible ischemic injury and loss of digits.

Angiography↗
PubMed1997

Alternative splicing of the primary Fas transcript generating soluble Fas antagonists is suppressed in the failing human ventricular myocardium.

Apoptosis of cardiomyocytes has been proposed as a factor contributing to severe heart failure. Since the trigger for apoptotic cellular suicide in nonischemic myocardium is unknown, we analyzed in human myocardial tissue the expression of the apoptosis-inducing membrane receptor Fas/APO-1 and of its alternatively spliced soluble isoforms which antagonize Fas by binding of the Fas ligand. Using reverse transcription polymerase chain reaction (RT-PCR) we found mRNA for Fas and 5 isoforms in nonfailing left ventricles, whereas Fas and only one isoform (FasExo6Del) were detectable in failing left ventricles. Standard calibrated, competitive RT-PCR revealed no significant increase of Fas mRNA in failing compared to nonfailing ventricles. However, the mRNA for FasExo6Del, expressed nearly on the same level as Fas in nonfailing ventricles, was decreased about 3-fold in failing ventricles. We propose that this altered expression of the Fas system renders the myocardium more susceptible for Fas-mediated apoptosis in end-stage heart failure.

Alternative Splicing↗
PubMed1997

Tumor necrosis factor alpha (TNF alpha) is cardiodepressant in pathophysiologically relevant concentrations without inducing inducible nitric oxide-(NO)-synthase (iNOS) or triggering serious cytotoxicity.

Cardiac hypertrophy and heart failure are frequently accompanied by elevated plasma levels of tumor necrosis factor alpha (TNF alpha), the pathogenetic relevance of this finding being a matter of debate. In human acute septic cardiomyopathy, on the other hand, the negative inotropic impact of TNF alpha on the heart is well documented and frequently ascribed to the induction of inducible nitric oxide (NO) synthase (iNOS) and an enhanced production of NO in the heart. Yet the present study presents evidence that in cardiomyocytes TNF alpha in non-toxic concentrations specifically depresses contractile performance independent of NO. In spontaneously beating neonatal rat cardiomyocytes, TNF alpha in a low, pathophysiologically relevant concentration (10 U/ml, 1-3 days) does not alter basal pulsation amplitude, but blocks alpha- and beta-adrenoceptor-stimulated increase in contractility and beating irregularity and impairs the impact of high extracellular calcium on contractile performance. However, this low TNF alpha-concentration does not suffice to induce iNOS - documented by reverse transcriptase polymerase chain reaction - or enhance nitrite concentrations in the cell culture supernatants as a measure of cellular NO production, neither in the presence nor absence of dexamethasone (0.1 micro M). Only in high concentration - the specific proinflammatory action being documented by an enhanced release of interleukin-6 from cardiomyocytes - TNF alpha (1000 U/mol; 6, 24 h) weakly induces the mRNA for iNOS, with a consecutive moderate rise in cellular nitrite production. TNF alpha-incubation (10-1000 U/ml) does not alter the morphological appearance of the cells displayed by phase contrast microscopy or evoke gross cytotoxicity.

Animals↗
PubMed1997

Expression and function of the cardiac Na+/Ca2+ exchanger in postnatal development of the rat, in experimental-induced cardiac hypertrophy and in the failing human heart.

The diastolic and systolic dysfunction in the failing heart appear to be related to the altered Ca2+ handling of the cardiac myocyte. Disturbed Ca2+ handling might also affect influx and efflux of other ions, including Na+. In this context, the cardiac sarcolemmal Na+/Ca2+ exchanger represents an important exchange mechanism of Ca2+ versus Na+ transport across the sarcolemma. Expression and function of cardiac Na+/Ca2+ exchanger is highest in newborn rats and declines gradually in postnatal development. In pressure overload-induced hypertrophy, expression of cardiac Na+/Ca2+ exchanger is increased and translated into increased Na+/Ca2+ exchanger activity similar to the early phase of postnatal development in the rat. This suggests a common underlying mechanism in the control of Na+/ Ca2+ exchanger expression in the immature and the hypertrophied myocardium. Similar to experimental-induced hypertrophy, mRNA, protein and activity of Na+/ Ca2+ exchanger is increased in the failing human heart suggesting an increase in the number of functional exchanger molecules rather than an enhanced exchange rate by preexisting exchanger molecules. The potential functional implications of an increased cardiac Na+/Ca2+ exchanger activity in human heart failure may be limitation of diastolic intracellular Ca2+ overload. However, this may increase the arrhythmogenic potential of the failing heart, since additional Na+ influx via Na+/Ca2+ exchanger may affect the membrane potential.

Aging↗
PubMed1996

Cardiac Na+/Ca2+ exchange activity in patients with end-stage heart failure.

OBJECTIVE: The aim of the present study was to investigate the functional activity and expression of the sarcolemmal Na+/Ca2+-exchanger in the failing human heart. METHODS: Left ventricular samples were taken from eleven patients with end-stage heart failure and six organ donors (normal controls). The Na+/Ca2+-exchanger activity was assessed by measuring Na+ gradient-induced 45Ca2+ transport into sarcolemmal vesicles of quantitatively collected crude membrane preparations. The abundance of the Na+/Ca2+-exchanger protein was determined by Western blot analysis using a specific antiserum and the results were normalized to myocyte specific beta-myosin heavy chain protein content. RESULTS: In membrane preparations of failing human hearts, both the Na+ gradient-induced 45Ca2+ transport activity and the level of immunoreactive Na+/Ca2+-exchanger protein were increased (P < 0.01) by 87% and 160% compared to controls, respectively. CONCLUSIONS: In human end-stage heart failure the increased sarcolemmal Na+/Ca2+-exchanger activity appears to be due to an elevated expression of this protein. An increase in the expression and activity of the Na+/Ca2+-exchanger in the failing human heart may be of important functional significance: while a resulting increase in Ca2+ extrusion across the sarcolemma may limit diastolic Ca2+ overload, a corresponding influx of Na+ may be associated with membrane depolarization and enhanced arrhythmogenesis if the Na+/Ca2+-exchanger operates primarily in the forward mode.

Adult↗
PubMed1995

Norplant removal facilitated by use of ultrasound for localization.

Two case reports are presented, describing the use of a 7-MHz ultrasound transducer to locate and visualize Norplant rods that could not easily be removed. The first patient was referred to the radiology department for a sonogram for unrelated reasons; her self-reported history led to the attempt to locate a retained Norplant rod. The second patient was first referred by a physician for the stated purpose of rod localization. After ultrasonic localization of the retained rods, both patients returned to their physicians' offices and underwent successful removal of the rods. Morbidity related to difficult rod retrieval can be reduced by using ultrasound for localization.

Adult↗
PubMed1994

Increased expression of endothelial constitutive nitric oxide synthase in rat aorta during pregnancy.

The mechanisms underlying enhanced vascular reactivity in pregnancy are not yet defined. In this study we have investigated the potential role of endothelium-derived vasodilator nitric oxide (EDNO). EDNO-mediated dilatory responses in vitro were markedly increased in aorta of pregnant as compared with nonpregnant rats. This increase in EDNO-releasability was accompanied by a two-fold increase in mRNA of endothelial constitutive nitric oxide synthase (NOS-III). Chronically substituted estrogen, but neither progesterone nor testosterone induced an upregulation of NOS-III mRNA in aorta of gonadectomized rats which amounted to about half that induced in aorta of pregnant rats. Thus, increased EDNO-releasability and increased NOS-III mRNA contribute to enhanced vascular reactivity in pregnancy.

Amino Acid Oxidoreductases↗
PubMed1994

Enrichment of fetal cells from maternal blood by high gradient magnetic cell sorting (double MACS) for PCR-based genetic analysis.

For simple and effective isolation of fetal cells from peripheral maternal blood, we combined depletion of maternal cells and enrichment of fetal cells by high-gradient magnetic cell separation (MACS). First CD45+ and CD14+ cells were depleted from maternal peripheral blood mononuclear cells by MACS. From the depleted fraction, CD71+ erythroid cells were enriched up to 80 per cent by MACS. This double-MACS' procedure yielded an average depletion rate of 780-fold and an average enrichment rate of 500-fold, with approximate recovery rates of 40-55 per cent. For paternity testing, cells from unseparated blood and the various fractions were analysed for polymorphism of the HLA-DQ-A1 locus and D1S80 locus by the polymerase chain reaction (PCR). In CD45-/CD71+ sorted cells from maternal blood, but not in unfractionated cells from maternal blood or CD45-/CD14- cells, paternal alleles could be detected. In the CD45-/CD71+ fraction, the relative frequency of paternal alleles compared with maternal alleles ranged from 1 in 20 to 1 in 200 (determined by titration and depending on the quality of separation and biological variation). In 7 out of 11 cases, between weeks 12 and 25 of gestation, we could identify paternal alleles by PCR, either HLA-DQ-A1 or D1S80. This double-MACS procedure is simple, fast, efficient, and reliable for non-invasive prenatal diagnosis.

Antigens, CD↗
PubMed1994

Vascular renin-angiotensin-system, endothelial function and atherosclerosis?

Clinical observations demonstrate an enhanced risk for myocardial infarction in patients with sustained activation of the local and/or systemic renin-angiotensin system, such as a high renin-sodium profile or a heritably enhanced expression of angiotensin converting enzyme. Chronic renin-angiotensin system blockade by angiotensin converting enzyme inhibition in patients with moderate heart failure reduces the rate of myocardial infarction and reinfarction. Preliminary experimental evidence suggests that these clinical observations may be partially explained by a proatherogenic effect of an activated renin-angiotensin system, which can downregulate the endothelial releasability of nitric oxide. Nitric oxide exerts many potentially antiatherogenic effects on endothelium, platelets and low density lipoproteins and indirectly on monocytes and leukocytes. Hypertension-induced chronic distension of elastic arteries upregulates the local renin-angiotensin system in these arteries and thereby downregulates nitric oxide releasability. Enhanced local synthesis of the trophic factor angiotensin-II and reduced releasability of the antitrophic factor nitric oxide appear to cooperate in the trophic adaptation of the distended vessel wall to the enhanced load, but with the disadvantage of enhanced susceptibility for atheroma development due to reduced releasability of nitric oxide. Chronic blockade of the renin angiotensin system by angiotensin converting enzyme inhibitors or by angiotensin receptor type-1 antagonists normalizes a reduced endothelial releasability of nitric oxide in several models, partially by a bradykinin-dependent mechanism. This endothelial protection proved to attenuate the progression of atherosclerosis in experimental models. The antiatherogenic potential of renin angiotensin system blockade in humans is presently under study.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1994

Comparative effects of chronic angiotensin-converting enzyme inhibition and angiotensin II type 1 receptor blockade on cardiac remodeling after myocardial infarction in the rat.

BACKGROUND: After myocardial infarction, the noninfarcted left ventricle develops reactive hypertrophy associated with a depressed coronary flow reserve, myocardial interstitial fibrosis, and reduced capillary density. The present study investigated the comparative cardiac effects of chronic angiotensin-converting enzyme (ACE) inhibition and selective angiotensin II type 1 receptor (AT1) blockade in the rat model of myocardial infarction and failure. METHODS AND RESULTS: Seven days after coronary ligation (MI), rats were randomized to enalapril (n = 8; 500 micrograms.kg-1.d-1), losartan (n = 9; 3 mg.kg-1.d-1), or placebo (n = 8) and treated for 6 weeks. Sham-operated rats (n = 10) served as controls. Coronary blood flow was measured with radiolabeled microspheres during baseline and maximal coronary dilation induced by dipyridamole (2 mg.kg-1.min-1 over 10 minutes). Right and left ventricular (LV) weight was increased in infarcted rats compared with sham-operated animals and enalapril- and losartan-treated MI rats. Minimal LV and right ventricular coronary vascular resistance was increased in MI rats but normalized with enalapril and losartan (LV:sham, 8.9; MI-placebo, 12.7; MI-enalapril, 9.2; MI-losartan, 8.8 mm Hg.mL-1.min-1.g-1, all P < .05 versus MI-placebo). Interstitial fibrosis determined from perfusion-fixed hearts was increased in infarcted rats but reduced by both enalapril and losartan. Myocardial capillary density improved with enalapril and losartan. In separate groups treated as above, plasma and tissue ACE activity was determined and demonstrated significantly higher ACE activity in noninfarcted LV tissue of MI-placebo rats compared with sham (0.64 vs 0.27 nmol.mg protein-1.min-1, P < .05). Enalapril and losartan reduced LV ACE activity (0.39 and 0.29 nmol.mg protein-1.min-1, P < .05 versus MI-placebo). CONCLUSIONS: The present study demonstrates that both chronic ACE inhibition and AT1 receptor blockade (1) reduces cardiac hypertrophy, (2) restores minimal coronary vascular resistance in postinfarction reactive hypertrophy, and (3) attenuates the development of myocardial interstitial fibrosis in the noninfarcted LV. These results suggest that inhibition of generation of angiotensin II and AT1 receptor blockade are equally effective in preventing important features of ventricular remodeling after myocardial infarction.

Angiotensin II↗
PubMed1994

Relation between myocardial function and expression of sarcoplasmic reticulum Ca(2+)-ATPase in failing and nonfailing human myocardium.

Expression of sarcoplasmic reticulum (SR) Ca(2+)-ATPase was shown to be reduced in failing human myocardium. The functional relevance of this finding, however, is not known. We investigated the relation between myocardial function and protein levels of SR Ca(2+)-ATPase in nonfailing human myocardium (8 muscle strips from 4 hearts) and in myocardium from end-stage failing hearts with dilated (10 muscle strips from 9 hearts) or ischemic (7 muscle strips from 5 hearts) cardiomyopathy. Myocardial function was evaluated by the force-frequency relation in isometrically contracting muscle strip preparations (37 degrees C, 30 to 180 min-1). In nonfailing myocardium, twitch tension rose with increasing rates of stimulation and was 76% higher at 120 min-1 compared with 30 min-1 (P < .02). In failing myocardium, there was no significant increase in average tension at stimulation rates above 30 min-1. At 120 min-1, twitch tension was decreased by 59% (P < .05) in dilated cardiomyopathy and 76% (P < .05) in ischemic cardiomyopathy compared with nonfailing myocardium. Protein levels of SR Ca(2+)-ATPase, normalized per total protein or per myosin, were reduced by 36% (P < .02) or 32% (P < .05), respectively, in failing compared with nonfailing myocardium. SR Ca(2+)-ATPase protein levels were closely related to SR Ca2+ uptake, measured in homogenates from the same hearts (r = .70, n = 16, and P < .005).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1994

Gene expression of the cardiac Na(+)-Ca2+ exchanger in end-stage human heart failure.

The regulation of cytosolic Ca2+ concentration during excitation-contraction coupling is altered in the failing human heart. Previous studies have focused on disturbances in Ca2+ release and reuptake from the sarcoplasmic reticulum (SR), whereas functional studies of the cardiac Na(+)-Ca2+ exchanger, another important determinant of myocyte homeostasis, are lacking for the failing human heart. Using a cardiac Na(+)-Ca2+ exchanger cDNA recently cloned from a guinea pig cDNA library, we investigated the gene expression of the cardiac Na(+)-Ca2+ exchanger in relation to the SR Ca(2+)-ATPase. Expression of both genes was quantified in left ventricular myocardium from 24 failing human cardiac explants and 7 control heart samples in relation to beta-myosin heavy chain mRNA by slot blot analysis. Compared with patients with nonfailing hearts, patients with dilated cardiomyopathy (DCM, n = 13) showed a 55% increase in Na(+)-Ca2+ exchanger mRNA levels (P < .05 versus control value) and a 41% increase in patients with coronary artery disease (CAD, n = 11). In the same hearts, SR Ca(2+)-ATPase mRNA levels were decreased by 50% in DCM and by 45% in CAD (P < .05 for both versus control value). There was a positive correlation between Na(+)-Ca2+ exchanger and SR Ca(2+)-ATPase mRNA levels both in normal and failing human hearts, albeit with different slopes and intercepts of the regression line. The Na(+)-Ca2+ exchanger protein levels as assessed by Western blot analysis and normalized to beta-myosin heavy chain protein were increased in DCM and CAD (P < .05 and P < .01 versus control value, respectively), whereas SR Ca(2+)-ATPase protein levels were reduced (P < .05 for both groups versus control values). Thus, the Na(+)-Ca2+ exchanger gene expression is enhanced in failing human hearts and may, in part, compensate for the depressed SR function with regard to diastolic Ca2+ removal.

Adult↗