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Biomedical subjects

J Neumann

Publications and source records attributed to J Neumann.

At least 37 records · Page 2Linked to original sources
PubMed2000

On the cardiac contractile, electrophysiological and biochemical effects of endothall, a protein phosphatase inhibitor.

Protein phosphatase inhibitors, e.g. cantharidin, exert positive inotropic effects in mammalian heart preparations. Endothall, a synthetic herbicide which is chemically related to cantharidin, inhibits protein phosphatase activities in mouse liver preparations. However, the cardiac effects of endothall have hitherto not been studied. In guinea pig papillary muscles, endothall (1-100 micromol/l) failed to affect force of contraction, whereas cantharidin (1-100 micromol/l) increased force of contraction maximally to 313.4 +/- 32% of control at 10 micromol/l. In isolated guinea pig ventricular cardiomyocytes, endothall did neither change the free intracellular calcium concentration nor the amplitude of calcium current nor the phosphorylation state of regulatory phosphoproteins like phospholamban. In contrast, cantharidin (30 micromol/l) increased the free intracellular calcium concentration and the L-type calcium current to 149.6 +/- 9% and to 157.6 +/- 12% of control, respectively. Furthermore, cantharidin (1-100 micromol/l) augmented the phosphorylation of phospholamban maximally to 140.8 +/- 7% of control. Nevertheless, in guinea pig ventricular homogenates, both endothall and cantharidin inhibited phosphatase activity with EC(50) values of 1.92 and 0.32 micromol/l, respectively. Thus, in contrast to cantharidin, endothall failed to increase force of contraction, though it inhibited protein phosphatase activity. Clearly, endothall is not an appropriate tool to study the function of protein phosphatases in the mammalian heart.

Animals↗
PubMed2000

Cantharidin enhances norepinephrine-induced vasoconstriction in an endothelium-dependent fashion.

In this study we characterized the effects of the protein phosphatase (PP) type 1 and type 2A inhibitor cantharidin (Cant) and its structural analogs cantharidic acid and endothall on PP activity, force of contraction, and myosin light chain phosphorylation in rat aorta. All compounds inhibited PP activity in homogenates of rat aorta with a rank order of potency of Cant = cantharidic acid > endothall. However, only Cant increased force of contraction and myosin light chain phosphorylation in intact isolated rat aortic rings. Based on these findings, we investigated the effects of Cant on alpha-adrenoceptor-mediated vasoconstriction. Cant (1 and 3 microM) enhanced norepinephrine-induced contraction in endothelium-intact rat aorta. In contrast, Cant did not affect norepinephrine-induced contraction in endothelium-denuded rat aorta. We suggest that inhibition of PP1 and/or PP2A activities by Cant enhances vascular contractility in endothelium-intact rat aorta by increasing the phosphorylation state of endothelial regulatory proteins.

Animals↗
PubMed2000

Functional properties of transgenic mouse hearts overexpressing both calsequestrin and the Na(+)-Ca(2+) exchanger.

Overexpression of calsequestrin (CSQ) induces severe cardiac hypertrophy, whereas overexpression of Na(+)-Ca(2+) exchanger (NCX) does not affect cardiac weight. To investigate a possible beneficial effect of NCX in hypertrophy, we produced transgenic mice overexpressing both NCX and CSQ (NCX/CSQ). Surprisingly, these mice developed severe heart failure. The heart/body weight ratio was enhanced and the mRNA expression of ANF, as a marker of hypertrophy, was highest in double transgenic mice. In isolated muscle strips, the basal relaxation time was prolonged in CSQ and NCX/CSQ mice. Moreover, in the presence of caffeine, force of contraction was increased only in CSQ and NCX/CSQ and was accompanied by elevated diastolic tension. In some respects, however, additional overexpression of NCX altered the CSQ phenotype into the wild-type phenotype. The expression of sarcoplasmic reticulum (SR)-Ca(2+)-ATPase and phospholamban, proteins involved in the Ca(2+) uptake of the SR, were only increased in CSQ, indicating a possible influence of NCX in the regulation of SR-Ca(2+) uptake proteins. The Ca(2+) transients and the L-type Ca(2+) currents in the presence of caffeine were very large in CSQ, but smaller increases were noted in double transgenic mice. Therefore, the successful co-overexpression of CSQ and NCX in these mice provides a novel model in which to investigate the interaction of proteins tightly linked to maintain Ca(2+) homeostasis.

Animals↗
PubMed2000

[Radical procedures on the thyroid gland at the turn of the millennium].

The increasing demands for radical thyroid operations by endocrinologists led during the last decade to elaboration of tactics and surgical techniques of thyroid operations. Nowadays as radical operation removal of all thyroid tissue is considered, and when malignancy is suspected, also removal of the affected lymph nodes. While in 1992 the ratio of radical thyroid operations did not exceed 30%, at present these operations account for more than 90%. Our experience is based on results assembled in a group of 4960 patients operated on account of thyroid disease with the conclusion, if judged with regard to postoperative complications, radical removal of the thyroid gland is nowadays almost equally safe as subtotal surgery. Sufficiently radical surgery prevents moreover a relapse of the disease. An essential part of treatment of thyroid disease should be interdisciplinary collaboration in particular among endocrinologists, sonographists and surgeons, not only during preoperative preparation but also during the regular postoperative follow up of patients.

Czech Republic↗
PubMed2000

Transcriptional regulation by cAMP in the heart.

Stimulation of the cAMP-dependent signalling pathway by beta-adrenergic catecholamines is an important physiological mechanism to increase contractile force in the heart. In addition to this, long-term beta-adrenergic stimulation by elevated catecholamines also influences the expressional control of functionally relevant cardiac regulatory proteins in human heart failure. The regulation of transcription by the cAMP-response element (CRE) is an important mechanism for a cAMP-mediated control of gene expression involved e.g. in spermiogenesis and memory/learning processes. This article discusses recent data leading to the hypothesis that this mechanism also contributes to altered gene regulation in heart failure.

Animals↗
PubMed1999

Expression of constitutive nitric oxide synthase in rat and human gastrointestinal tract.

The aim of this study was to determine the expression of constitutive NO synthases (ecNOS and bNOS) at the protein level in rat and human gastrointestinal tract. We established a quantitative Western blotting method for detection and quantification of ecNOS and bNOS in both species. Human gastric fundus was further analyzed by immunohistochemistry. EcNOS expression at the protein level could be quantified in different organs of the rat gastrointestinal tract and in human gastric mucosal biopsies. Immunohistochemistry of gastric fundus revealed that immunoreactivity for ecNOS was localized mainly in the endothelium of small vessels. In rats, expression of bNOS at the protein level was highest in esophagus. By means of immunohistochemistry of human gastric fundus, immunoreactivity was detected mainly in the plexus of Auerbach. We conclude that isoforms of constitutive nitric oxide synthase can be identified and quantified at the protein level both in rat and human gastrointestinal tract. The presence of bNOS in nerve tissue supports previous observations that NO serves as a transmitter in non-adrenergic, non-cholinergic nerves in human esophagus and stomach. The observation that ecNOS has been found mainly in endothelial cells suggests the involvement of NO in the regulation of mucosal blood flow.

Aged↗
PubMed1999

Expression of cardiac calcium regulatory proteins in atrium v ventricle in different species.

The duration of contraction in isolated electrically driven preparations from atrium and ventricle of mouse, rat, rabbit, guinea-pig and dog was consistently shorter in atrial compared to ventricular preparations. Overexpression of phospholamban (PLB) in transgenic mice prolonged duration of contraction, underscoring the importance of PLB for kinetics of cardiac contractility. The expression of regulatory proteins was studied by Western and Northern blot analysis. In rat myocardium, expression of the sarcoplasmic reticulum Ca2+ ATPase (SERCA) was higher in atrium than in ventricle, as was also observed in the rabbit, guinea-pig and wild-type mouse samples. Canine myocardium, however, had similar levels of SERCA (protein and mRNA) in atrium and ventricle. PLB and calsequestrin on protein and RNA levels were lower in atrium than in ventricle from rat, rabbit, guinea-pig and wild-type mouse. PLB protein and RNA levels were higher in ventricle than in atrium at ages 1 and 5 days postnatally and in adult rats. SERCA protein and RNA levels were higher in ventricle than in atrium at days 1 and 5 after birth, but lower in ventricle than in atrium in adult rats. In dog, the calsequestrin level was identical in atrium and ventricle (protein and mRNA) and PLB did not differ between atrium vs ventricle at the protein level but was lower at the mRNA level. Also, Ca2+ uptake was higher in atrium than in ventricle in the dog samples. The expression of the inhibitory subunit of troponin was unchanged between atrium and ventricle in all species studied (protein and mRNA). In dog, protein expression of triadin and junctin was lower in atrium vs ventricle. Triadin mRNA was not altered in dog atrium vs ventricle. In summary, while the hastened relaxation of atrium vs ventricle correlates in part with the lower expression of PLB and higher expression of SERCA, altered regional expression of other SR proteins handling Ca2+ may also play an important role in some species.

Animals↗
PubMed1999

[Spontaneous splenic rupture with diffused angiomatosis of the spleen].

The diffuse angiomatosis of the spleen is a rare splenic proliferation. Spontaneous rupture is the main, potentially lethal complication, found in 25% of cases. The problem with these vascular tumors is preoperative diagnosis, because they are asymptomatic for a long time. First-choice therapy is limited resection. In the case of rupture, splenectomy is a life-saving procedure. We report on a 56-year-old woman with a spontaneous splenic rupture as the first symptom of diffuse angiomatosis of the spleen. Exceptional features of splenic hemangiomas, causes of spontaneous rupture and the therapy are described.

Angiomatosis↗
PubMed1999

Effect of 2,3-butanedione monoxime on force of contraction and protein phosphorylation in bovine smooth muscle.

The aim of the study was to investigate the effects of the putative protein phosphatase (PP) activator 2,3-butanedione monoxime (BDM) in vascular smooth muscle. BDM concentration-dependently increased PP activity in homogenates of bovine coronary arteries and led to dephosphorylation of various smooth muscle proteins in 32P-labelled bovine aortic smooth muscle cells. In isolated bovine coronary artery rings (CARs) the effects of 10 mmol/l BDM on force of contraction (FOC) under conditions of depolarization by 75 mmol/l KCl and PP inhibition by 100 micromol/l cantharidin were investigated. At the end of contraction experiments CARs were freeze-clamped and myosin light chain (MLC20) phosphorylation was determined by two-dimensional gel electrophoresis. Pretreatment of CARs with BDM reduced KCl-induced FOC to 42+/-4% vs. 118+/-1% (no BDM) and cantharidin-induced FOC to 102+/-2% vs. 120+/-7% (no BDM) compared to a former KCl contraction (= 100%). Moreover, BDM increased the amount of unphosphorylated MLC20 up to 56+/-2% vs. 36+/-5% (no BDM) and 28+/-2% vs. 21+/-1% (no BDM), respectively, demonstrating the central role of MLC20 phosphorylation in initiating smooth muscle contraction. In KCl precontracted CARs BDM decreased FOC to 47+/-4% vs. 100+/-1% (no BDM) but did not affect MLC20 phosphorylation, suggesting an uncoupling of force maintenance and MLC20 phosphorylation. In contrast, BDM neither affected FOC nor MLC20 phosphorylation in CARs precontracted with cantharidin. These results strengthen the hypothesis that PP activation by BDM only occurs on the holoenzyme level, e.g. by affecting regulatory subunits.

Animals↗
PubMed1999

Inositol-1,4,5-trisphosphate increase by diadenosine tetraphosphate in preparations from failing human myocardium.

In human ventricular trabeculae carneae 100 microM AP4A (diadenosine tetraphosphate) increased force of contraction to 162.8+/-15.7% of predrug value (n=9). This positive inotropic effect was accompanied by a prolongation of time parameters: time to peak tension and time of relaxation were prolonged by 7.8+/-1.3% and 14.9+/-3.8%, respectively (P<0.05). In the same trabeculae, AP4A increased IP3 (inositol-1,4,5-trisphosphate) content from 9.0+/-1.3 pmol/mg to 22.9+/-5.4 pmol/mg protein (n=5-9). In conclusion, the positive inotropic effect of AP4A in the human myocardium is likely due to an increase of IP3 mediated probably via Gq-coupled P2Y-purinoceptors. Because of the prominent role of Gq in the development of cardiac disease, these findings may lay the ground to further investigate the possible role of AP4A and/or related ligands (e.g. AP2A and AP3A) in heart failure.

Cardiomyopathies↗
PubMed1999

On the contractile function of protein phosphatases in isolated human coronary arteries.

It is unknown whether protein phosphatases types 1 and 2A are present in and can regulate the tone of human vascular tissue. The expression and possible function of serine/threonine protein phosphatases (PP) type 1 (PP1) and type 2A (PP2A) were studied in isolated human coronary arteries. Catalytic subunits of PPI and PP2A were identified by means of phosphatase activity measurement in tissue homogenates, by separation of enriched extracts through affinity column chromatography, by immunoblotting with specific antibodies, by hybridization of mRNA with specific DNA probes and PCR of reverse transcribed mRNA. Based on these methods, the catalytic subunits of PP1(alpha,beta,gamma) and PP2A(alpha,beta) were identified. Appropriately, cantharidin, an inhibitor of PP1 and PP2A, increased basal tone of human isolated coronary artery rings with an EC50 of about 16 micromol/l by increasing the phosphorylation state of the regulatory light chains of myosin. In summary, PP1 and PP2A are expressed in human coronary arteries and they can alter vascular tone.

Chromatography, Affinity↗
PubMed1999

Activity of cAMP-dependent protein kinase and Ca2+/calmodulin-dependent protein kinase in failing and nonfailing human hearts.

OBJECTIVES: A hallmark of human heart failure is prolonged myocardial relaxation. Although the intrinsic mechanism of phospholamban coupling to the Ca(2+)-ATPase is unaltered in normal and failed human hearts, it remains possible that regulation of phospholamban phosphorylation by cAMP-dependent mechanisms or other second messenger pathways could be perturbed, which may account partially for the observed dysfunctions of the sarcoplasmic reticulum (SR) associated with this disease. METHODS: cAMP-dependent protein kinase (PKA) and Ca2+/calmodulin-dependent protein kinase II (CaM kinase) were characterized initially by DEAE-Sepharose chromatography in hearts from patients with end-stage dilated cardiomyopathy. We measured the activity of PKA and CaM kinase in left ventricular tissue of failing (idiopathic dilated cardiomyopathy; ischemic heart disease) and nonfailing human hearts. RESULTS: Basal PKA activity was not changed between failing and nonfailing hearts. One major peak of CaM kinase activity was detected by DEAE-Sepharose chromatography. CaM kinase activity was increased almost 3-fold in idiopathic dilated cardiomyopathy. In addition, hemodynamical data (left ventricular ejection fraction, cardiac index) from patients suffering from IDC positively correlate with CaM kinase activity. CONCLUSIONS: Increased CaM kinase activity in hearts from patients with dilated cardiomyopathy could play a role in the abnormal Ca2+ handling of the SR and heart muscle cell.

Adult↗
PubMed1999

Regional expression of phospholamban in the human heart.

BACKGROUND: Several independent lines of evidence indicate that phospholamban (PLB) expression correlates positively with depression of force of contraction and duration of contraction in isolated cardiac preparations of several animal species. Here, we studied whether PLB levels correlate with attenuation of contractility and enhancement of contractile time parameters in different parts of the human heart. METHODS: Force of contraction was measured in isolated electrically driven atrial and ventricular preparations from human hearts. Ca(2+)-uptake by human atrial and ventricular homogenates was assayed at different ionized Ca(2+)-concentrations. Protein expression of PLB and the sarcoplasmic Ca(2+)-ATPase (SERCA) was measured in homogenates by quantitative immunoblotting using specific antibodies. PLB mRNA expression was quantified in human cardiac preparations by Northern blot analysis. RESULTS: The duration of contraction in isolated preparations of human right ventricle (RV) was double that found in right atrial preparations (RA) (620 +/- 25 ms versus 308 +/- 15 ms). In RA, PLB expression was reduced by 44% at the protein level and by 34% at the mRNA level compared to RV. In contrast, the SERCA protein content was increased by 104% in RA compared to RV. Ca(2+)-uptake at low ionized Ca(2+)-concentration, where the inhibiting effect of PLB is maximal, amounted to 1.39 +/- 0.28 nmol Ca2+/mg protein in RA and to 0.62 +/- 0.09 nmol Ca2+/mg protein in RV (n = 6 both). CONCLUSIONS: It is suggested that duration of contraction is shorter in human atrium versus ventricle due to the combined effect of decreased PLB levels (which inhibits SERCA function) and increased SERCA levels. The lower relative ratio of PLB to SERCA leads to less inhibition of SERCA and increased Ca(2+)-uptake which enhances relaxation and contraction in human atrium.

Atrial Natriuretic Factor↗