PubMed Health⌕ Search

Biomedical subjects

B Ek

Publications and source records attributed to B Ek.

At least 55 records · Page 3Linked to original sources
PubMed1994

Reoxygenation-induced cell damage of isolated neonatal rat ventricular myocytes can be reduced by chain-breaking antioxidants.

To study the role of chain-breaking antioxidants on reperfusion injury in the ischemic heart, cultured ventricular heart cells (myocytes) were subjected to hypoxia and reoxygenation. The myocytes were prepared from neonatal rats and cultured in F10 medium that was supplemented with serum. As a marker for cell damage, lactate dehydrogenase was analyzed in the medium. Cells subjected to hypoxia for 5 h showed a 1.9 fold increase in lactate dehydrogenase (LD) leakage, while cells subjected to 1 h hypoxia followed by 4 h reoxygenation showed a 5-fold increase in LD intake. Alpha-tocopherol, beta-carotene, nordihydroguairetic acid (NDGA), butylated hydroxyltoluene (BHT), and ICI211965 were added to the cell medium every 24 h for 6 d prior to reoxygenation. All compounds protected against reoxygenation-induced cell damage. In the presence of the 5-lipoxygenase inhibitor ICI211965, protection against LD leakage was found only at high concentrations, which corresponded to the antioxidative effect of ICI211965, and not to inhibition of 5-lipoxygenase. We conclude that cultured ventricular myocytes can be used to evaluate the protective effect of antioxidants on reoxygenation-induced cell damage, and that chain-breaking antioxidants protected well against reoxygenation-induced cell damage.

Animals↗
PubMed1994

Purification and characterization of an extracellular serine protease from the nematode-trapping fungus Arthrobotrys oligospora.

When grown in liquid cultures allowing the formation of nematode traps, the fungus Arthrobotrys oligospora produced two extracellular proteases hydrolysing the chromogenic substrate Azocoll. The protease activity was separated into two fractions (FI and FII) using anion-exchange chromatography. In bioassays, protease(s) present in FII immobilized the free-living nematode Panagrellus redivivus indicating that the enzyme(s) might be involved in the infection of nematodes. A protease designated PII was purified from FII to apparent homogeneity by hydrophobic interaction and size-exclusion chromatography, resulting in an approximately 15-fold increase in specific activity. The purified enzyme was glycosylated, had a molecular mass of approximately 35 kDa (gel filtration) and an isoelectric point of pH 4.6. PII immobilized P. redivivus in bioassays and hydrolysed proteins of the purified cuticle. The enzyme hydrolysed several protein substrates including casein, bovine serum albumin and gelatin, but not native collagen. Examination of substrate specificity with synthetic peptides showed that PII readily hydrolysed tripeptides with aromatic or basic amino acids including N-benzoyl-L-phenylalanyl-L-valyl-L-arginine-4-nitroanilide (Bz-Phe-Val-Arg-NA) and succinyl-glycyl-glycyl-L-phenylalanine-4-nitroanilide (Suc-Gly-Gly-Phe-NA). Mono-peptides were hydrolysed at considerably slower rates. PII had an optimum activity between pH 7 and 9 and was susceptible to autodegradation. PII was inhibited by several serine protease inhibitors including phenylmethylsulfonyl fluoride (PMSF), chymostatin and antipain. The protease was N-terminally blocked, but the sequence of one internal peptide showed a high homology with a region containing the active site histidine residue of the subtilisin family of serine proteases.

Amino Acid Sequence↗
PubMed1993

Characterization of the 97 and 103 kDa forms of starch branching enzyme from potato tubers.

N-Terminal analysis, peptide mapping and partial peptide sequencing of the 97 and 103 kDa forms of starch branching enzyme from potato tubers showed that the two forms are highly related. A comparison with sequence data in the literature showed that these forms belong to the starch branching enzyme isoform I family. An internal cDNA fragment was obtained using PCR technology on potato tuber RNA with two oligonucleotide primers constructed from the peptide sequence data. Southern blot analysis using the PCR fragment as probe showed that there is only one gene locus encoding this isoform of the enzyme in Solanum tuberosum as well as in Solanum commersonii.

1,4-alpha-Glucan Branching Enzyme↗
PubMed1993

Differential expression of myrosinase gene families.

In mature seeds of Brassica napus three major and three minor myrosinase isoenzymes were identified earlier. These myrosinases are known to be encoded by at least two different families of myrosinase genes, denoted MA and MB. In the work described in this paper the presence of different myrosinase isoenzymes in embryos, seedlings, and vegetative mature tissues of B. napus was studied and related to the expression of myrosinase MA and MB genes in the same tissues to facilitate future functional studies of these enzymes. In developing seeds, myrosinases of 75, 73, 70, 68, 66, and 65 kD were present. During seedling development there was a turnover of the myrosinase pool such that in 5-d-old seedlings the 75-, 70-, 66-, and 65-kD myrosinases were present, with the 70- and 75-kD myrosinases predominating. In 21-d-old seedlings the same myrosinases were present, but the 66- and 65-kD myrosinase species were most abundant. At flowering the mature organs of the plant contained only a 72-kD myrosinase. MA genes were expressed only in developing seeds, whereas MB genes were most highly expressed in seeds, seedling cotyledons, young leaves, and to a lesser extent other organs of the mature plant. During embryogenesis of B. napus, myrosinase MA and MB gene transcripts started to accumulate approximately 20 d after pollination and reached their highest level approximately 15 d later. MB transcripts accumulated to about 3 times the amount of MA transcripts. In situ hybridization analysis of B. napus embryos showed that MA transcripts were present predominatly in myrosin cells in the axis, whereas MB genes were expressed in myrosin cells of the entire embryo. The embryo axiz contained 75-, 70-, and 65-kD myrosinases, whereas the cotyledons contained mainly 70- and 65-kD myrosinases. Amino acid sequencing revealed the 75-kD myrosinase to be encoded by the MA gene family. The high degree of cell and tissue specificity of the expression of myrosinase genes suggests that studies of their transcription should provide interesting information concerning a complex type of gene regulation.

Amino Acid Sequence↗
PubMed1993

Oesophageal dysfunction in familial amyloidosis with polyneuropathy.

Sixteen patients with familial amyloidosis and polyneuropathy (FAP) and 14 health subjects underwent oesophageal manometry. Six of the patients had a severe oesophageal dysmotility with almost completely abolished propulsive pressure waves on swallowing in the lower 2/3 of the oesophagus. Ten patients had moderate dysfunction with reduced propulsive pressure wave amplitudes. Neostigmine increased the pressure wave amplitudes in healthy subjects but less so in the FAP patients. Scopolamine (Scopyl)-terbutaline (Bricanyl) almost abolished the propulsive pressure waves in healthy subjects and all patients in the lower 2/3 of the esophagus. Oesophageal distensibility, tested by inflating a rubber balloon in the oesophagus, was similar in FAP patients and healthy subjects. Thus, it is unlikely that amyloid deposits in the mucosal wall increased the oesophageal stiffness. An autonomic, predominantly vagal, denervation probably explains the disturbed function.

Adult↗
PubMed1993

Studies of muscarinic receptor reserve linked to phosphoinositide hydrolysis in parotid gland and cerebral cortex.

Hydrolysis of inositol phospholipids caused by muscarinic agonists was studied in the guinea-pig parotid gland (PG) and cerebral cortex (CX). The present study describes the effect of two muscarinic agonists, carbachol and oxotremorine, on stimulation of phosphoinositide hydrolysis and on binding of [3H]NMS in the presence of the irreversible muscarinic antagonist benzilyl choline mustard (BCM). Carbachol and oxotremorine stimulated the formation of inositol phosphates in PG, pD2(Carb) = 5.3 +/- 0.1, pD2(Oxo) = 5.9 +/- 0.1 and in CX, pD2(Carb) = 4.3 +/- 0.2, pD2(Oxo) = 5.8 +/- 0.2. In the present study slices from both tissues have been exposed to 0.1 microM BCM for 2, 5 and 10 min. Treatment for 10 min caused a 75-85% reduction in specific [3H]N-methyl scopolamine ([3H]NMS) binding sites in both PG and CX. Following 2 min BCM treatment of PG a marked decrease in pD2 value of the carbachol-stimulated inositol phosphate formation was found. This effect was not found in CX. The results showed that a 30-40% reduction in binding sites shifted the carbachol concentration response curve to the right by one order of magnitude and reduced the oxotremorine-induced release of inositol phosphates by approximately 20%. In PG, the BCM-induced reduction of the carbachol-stimulated inositol phosphate formation was paralleled by the reduction in receptor binding sites. Similar treatment, but in CX, showed a lower reduction of the carbachol-stimulated inositol phosphate formation as compared to the reduction in receptor-binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Purification and characterization of a surface lectin from the nematode-trapping fungus Arthrobotrys oligospora.

Several studies have indicated that the capture of nematodes by the nematophagous fungus Arthrobotrys oligospora is mediated by a lectin on the fungal surface. One of the major surface proteins of this fungus showed haemagglutinating activity and was isolated by affinity chromatography using a mucin Sepharose column. Biochemical analysis showed that the protein was a dimeric glycoprotein with a molecular mass of 36 kDa and an isoelectric point of pH 6.5, and contained no sulphur amino acids. The protein was N-terminally blocked; four internal peptides were sequenced, and showed no significant similarity to sequences in the Swiss-Prot or PIR databases. The haemagglutinating activity of the isolated protein was not inhibited by any of the mono- or disaccharides tested, but it was inhibited by the glycoproteins fetuin and mucin. The haemagglutinating activity changed after incubating the protein in buffers of different pH, with maximal activity at pH 11.0 and no activity at pH 2.8. The lectin was tested for different enzymic activities but none were detected. Analysis of the haemagglutinating activity in various cell fractions indicated that the protein was associated with extracellular polymer layers and with the cell wall of the fungus. About the same amount of the haemagglutinating protein was recovered from samples of vegetative mycelium and of mycelium containing nematode-trapping cells.

Amino Acid Sequence↗
PubMed1991

Correlation between oxidation of low density lipoproteins and prostacyclin synthesis in cultured smooth muscle cells.

The effect of antioxidants on the oxidation of low density lipoproteins in relation to prostacyclin synthesis was investigated in the prescence of rabbit smooth muscle cells (SMC) and Fe-containing culture medium. The lipid peroxidation of low density lipoproteins (LDL) assayed as thiobarbituric acid reactive substances was increased from 0.5 to 1.4 nmol malondialdehyde/mL by the presence of smooth muscle cells. Two potent antioxidants, nordihydroguairetic acid (NDGA) and butylated hydroxytoluene (BHT), inhibited lipoprotein oxidation by IC50 values of 0.2 and 0.8 microM, respectively. Inhibition of lipoprotein oxidation was associated with an increased prostacyclin synthesis by the SMC, the effect being more pronounced with nordihydroguairetic acid than with butylated hydroxytoluene. The stable metabolite of the lipid hydroperoxide, 15-hydroxyeicosatetraenoic acid (15-HETE), formed in the 15-lipoxygenase pathway was measured following antioxidant treatment and found to be eliminated or greatly reduced by both antioxidants. The results presented show that lipid hydroperoxides, formed as a consequence of lipoprotein oxidation and promoted by the smooth muscle cells through a lipoxygenase reaction, may regulate prostacyclin synthase, a process which may be influenced by the addition of antioxidants.

Animals↗
PubMed1991

The 1,4-beta-D-glucan glucanohydrolases from Phanerochaete chrysosporium. Re-assessment of their significance in cellulose degradation mechanisms.

A physico-chemical, functional and structural characterization, including partial sequence data, of three major 1,4-beta-D-glucan glucanohydrolases (EC. 3.2.1.4) isolated from the culture filtrate of the white-rot fungus Phanerochaete chrysosporium, shows that all three enzymes belong to a single family of cellulases. EG44, pI 4.3, (named after its apparent molecular mass in kDa), shows a clear homology with Schizopyllum commune Endoglucanase I (EGI); whereas EG38, pI 4.9, (named in the same manner) is related more closely to Trichoderma reesei (Trichoderma longibrachiatum) Endoglucanase III (EGIII). EG36, pI 5.6-5.7, is probably an EG38 protein lacking its cellulose binding domain. Strong synergistic action is induced by the enzymes acting in concert with cellobiohydrolases (CBHI and CBHII) from the same organism, indicating a highly effective enzymatic system for cellulose degradation. Controlled proteolysis with papain has allowed a so far unique cleavage of endoglucanases EG44 and EG38 into two domains: a core protein, which virtually lacks the capacity to absorb onto microcrystal-line cellulose but retains full catalytic activity against carboxymethyl cellulose and low molecular weight soluble substrates; and a peptide fragment corresponding to the cellulose binding domain. The latter appears to be of paramount significance in the mechanisms involved in the hydrolysis of microcrystalline cellulose.

Amino Acid Sequence↗
PubMed1990

Deletion of the kinase insert sequence of the platelet-derived growth factor beta-receptor affects receptor kinase activity and signal transduction.

A characteristic feature of the platelet-derived growth factor (PDGF) beta-receptor is the presence of an insert sequence in the protein tyrosine kinase domain. A receptor mutant which lacks the entire insert of 98 amino acids was expressed in CHO cells, and its functional characteristics were compared with those of the wild-type receptor. The mutant receptor bound PDGF-BB with high affinity and mediated internalization and degradation of the ligand with efficiency similar to that of the wild-type receptor but did not transduce a mitogenic signal. It was found to display a decreased autophosphorylation after ligand stimulation and had a decreased ability to phosphorylate exogenous substrates; phosphofructokinase was not phosphorylated at all, whereas a peptide substrate was phosphorylated, albeit at a lower rate compared with phosphorylation by the wild-type receptor. Furthermore, the mutant receptor did not mediate actin reorganization but mediated an increase in c-fos expression. The data indicate that the insert in the kinase domain of the PDGF beta-receptor is important for the substrate specificity or catalytic efficiency of the kinase; the deletion of the insert interferes with the transduction of some, but not all, of the signals that arise after activation of the receptor.

Animals↗
PubMed1988

Muscarinic receptor coupling to inositol phospholipid metabolism in guinea-pig cerebral cortex, parotid gland and ileal smooth muscle.

Inositol phospholipid hydrolysis induced by agonist-stimulation of muscarinic receptors has been examined in slices of guinea-pig cerebral cortex, parotid gland and ileal smooth muscle. An assay measuring 3H-inositol phosphate formation from prelabelled lipids in the presence of LiCl, allowed marked stimulation by agonists to be followed. The pD2-value of carbachol differed markedly, between tissues being more than 10-fold lower in cerebral cortex than in parotid gland. The partial agonist oxotremorine showed the largest relative maximal responsiveness in parotid gland, followed by ileum and cortex. Atropine suppressed the phosphoinositide response to carbachol with an almost similar affinity in each tissue, but pirenzepine was found to have a 20-fold higher affinity in cerebral cortex, pKi = 7.7 than in parotid gland, pKi = 6.3. Carbachol, even in the presence of guanosine triphosphate (GTP), displayed complex binding against 3H-N-methylscopolamine (3H-NMS) in cortical and ileal membranes, though in membranes from the parotid gland a single homogeneous population was found. Atropine inhibition of 3H-NMS parallelled its suppression of the phosphoinositide response, the affinities in each tissue studied being similar. Pirenzepine inhibited binding from two components in cerebral cortex, the high affinity value being similar to that obtained in the phosphoinositide assay. In parotid gland, however, only low affinity pirenzepine binding sites were observed, closely resembling the affinity found for this antagonist in the functional assay. These experiments suggest (a) that there are differences between agonist occupation of muscarinic receptors and phosphoinositide hydrolysis within the different tissues, (b) that both high and low affinity pirenzepine binding sites appear to be linked to phosphoinositide metabolism, and (c) that low affinity pirenzepine sites may be more efficiently coupled to the hydrolysis of phosphoinositides.

Animals↗
PubMed1988

The beta 1- and beta 2-adrenoceptor affinity of atenolol and metoprolol. A receptor-binding study performed with different radioligands in tissues from the rat, the guinea pig and man.

The radioligand binding technique was used to perform a systematic investigation of the beta 1- and beta 2-adrenoceptor affinity of atenolol and metoprolol in tissues from the rat, the guinea pig and man. Radioligands, [125I](+/-)hydroxybenzylpindolol, [125I](-)pindolol, [3H](-)dihydroalprenolol and [3H](-)CGP12177, with different degrees of lipophilicity were used in the binding experiments. In membrane preparations of rat ventricular myocardium and uterus, the number of specific binding sites was similar when comparing experiments performed with the different radioligands. The percentage of the beta 1- and beta 2-adrenoceptor subpopulations in the tissues studied was not dependent on the radioligand or displacing compound used. Furthermore, the affinity of metoprolol and atenolol for beta 1- and beta 2-adrenoceptors was independent of the radioligand used or the tissue studied. The beta 1-adrenoceptor affinity of metoprolol was about 6-7 times higher than that of atenolol, while the beta 1-adrenoceptor selectivity was similar (about 30-fold) for the two beta-blockers. It is concluded that the physical-chemical properties of the radioactive ligands and beta-blockers studied do not affect the results obtained from beta-adrenoceptor-binding experiments in cellular membrane fractions. The beta 1- and beta 2-adrenoceptor affinities did not change in any experiments performed in tissues from the rat, the guinea pig and man for either atenolol or metoprolol.

Animals↗
PubMed1988

Muscarinic receptor interaction with full and partial beta-adrenoceptor agonists in the rat colon strip.

beta-Adrenoceptor agonists inhibit contractile activity in isolated colon strips. In order to demonstrate that beta-adrenoceptors are located at different functional levels within the colon wall, increasing concentrations of muscarinic agonists were used to interact functionally with the beta-adrenoceptor-mediated inhibition of spontaneous colon activity. The effects of the full agonists isoprenaline and terbutaline and of the partial agonist prenalterol were functionally antagonized by carbachol (0.03 and 0.3 mumol/l) and bethanechol (1.3 and 30 mumol/l). This functional antagonism was parallelled by an increase in baseline tension and spontaneous contractile activity of the isolated colon strip. At lower concentrations of carbachol (0.003 and 0.01 mumol/l) or bethanechol (0.03 and 0.3 mumol/l) no effect on the contractile status of the smooth muscle or on the pD2-values of the full agonists was seen. However, at these lower concentrations of muscarinic agonists a marked decrease in the maximal inhibitory response to the partial beta-adrenoceptor agonist prenalterol was demonstrated. The inhibitory response to prenalterol showed a biphasic concentration-response curve. The muscarinic antagonist atropine produced an increase in the maximal response of the high potency component of the concentration-response curve for prenalterol and an increase in the sensitivity to isoprenaline. These results demonstrate the presence of a high cholinergic tone in the colon preparation of a magnitude that clearly reduces the sensitivity to beta-adrenoceptor agonists. The different responses to full and partial beta-adrenoceptor agonists in the presence of increasing concentrations of muscarinic agonists may indicate that beta-adrenoceptors are located on two different functional units within the colon wall.

Adrenergic beta-Agonists↗
PubMed1988

cDNA cloning and expression of a human platelet-derived growth factor (PDGF) receptor specific for B-chain-containing PDGF molecules.

The structure of the human receptor for platelet-derived growth factor (PDGF) has been deduced through cDNA cloning. A 5.45-kilobase-pair cDNA clone predicts a 1,106-amino-acid polypeptide, including the cleavable signal sequence. The overall amino acid sequence similarity with the murine PDGF receptor is 85%. After transcription of the cDNA and translation in vitro, a PDGF receptor antiserum was used to immunoprecipitate a product of predicted size, which also could be phosphorylated in vitro. Stable introduction of the cDNA into Chinese hamster ovary (CHO) cells led to the expression of a 190-kilodalton component, which was immunoprecipitated by the PDGF receptor antiserum; this most probably represents the mature PDGF receptor. Binding assays with different 125I-labeled dimeric forms of PDGF A and B chains showed that the PDGF receptor expressed in CHO cells bound PDGF-BB and, to a lesser extent, PDGF-AB, but not PDGF-AA.

Amino Acid Sequence↗
PubMed1987

Purification of the receptor for platelet-derived growth factor from porcine uterus.

The receptor for platelet-derived growth factor has been purified to homogeneity on a large scale from porcine uterus. The purification procedure utilizes solubilization of uterus membranes by Triton X-100, followed by sequential chromatographies on wheat germ agglutinin-Sepharose, fast protein liquid chromatography Mono-Q, and anti-phosphotyrosine-Sepharose. About 160 micrograms of homogeneous and functionally active 170-kDa receptor could be purified from 5 kg of uterus tissue. The pure receptor responded to platelet-derived growth factor stimulation by autophosphorylation, indicating that the receptor has a kinase domain as an integral part of the molecule. A rabbit antiserum was produced against the pure receptor, which specifically recognizes the intact 170-kDa receptor.

Animals↗
PubMed1987

Nicardipine in the treatment of essential hypertension controlled 6-month-study comparing nicardipine with propranolol at rest and during exercise.

Thirty patients with mild to moderate essential hypertension entered a randomised double-blind parallel group study for 6 months to compare the effects of the new calcium channel blocker nicardipine 90 mg/day and propranolol 240 mg/day. Both drugs reduced systolic and diastolic blood pressures significantly in the supine and in standing positions. After 6 months of treatment, nicardipine had reduced the supine systolic and diastolic blood pressures by 16 and 17 mm Hg, respectively, and propranolol by 15 and 12 mm Hg. While propranolol treatment led to a marked decline in heart rate, nicardipine caused a small but statistically significant increase in heart rate throughout the study. Both drugs reduced blood pressure during maximal exercise, but propranolol had a greater effect. During exercise nicardipine did not affect the heart rate, whereas propranolol dramatically reduced it. Nicardipine did not produce any ECG changes at rest or during exercise. The side-effects for nicardipine were mild and were related to the vasodilatation induced by the drug. No abnormalities in routine blood chemical tests were found for either of the drugs. Nicardipine appears to be an effective single drug treatment for mild to moderate hypertension.

Adult↗