PubMed Health⌕ Search

Biomedical subjects

B Herman

Publications and source records attributed to B Herman.

At least 37 records · Page 2Linked to original sources
PubMed1991

Early PDGF-induced alterations in cytosolic free calcium are required for mitogenesis.

Early alterations in cytosolic free Ca2+ concentration (Ca2+i) (occurring within seconds to minutes) following platelet-derived growth factor (PDGF) stimulation were demonstrated to be required, in both BALB/c3T3 fibroblasts and vascular smooth muscle cells, for subsequent DNA synthesis by introduction of Ca(2+)-antagonists at different times in relation to growth factor stimulation. Blockade of PDGF-stimulated increases in Ca2+i correlated with inhibition of PDGF-stimulated DNA synthesis in both systems, although the mechanism of increased Ca2+i is different in the two cell types. In vascular smooth muscle cells, voltage-sensitive Ca(2+)-channel antagonists, TPA, and pertussis toxin inhibited both PDGF-induced increases in Ca2+i and DNA synthesis when added immediately before PDGF, but did not do so when added for the same time period 4 hr after PDGF. Similarly, pretreatment of fibroblasts with TMB-8 inhibited PDGF-induced alterations in Ca2+i and DNA synthesis, but had no effect on DNA synthesis when added after PDGF exposure. These findings demonstrate for the first time that early increases in Ca2+i stimulated by PDGF play a critical role in PDGF-stimulated mitogenesis.

Animals↗
PubMed1990

Cytosolic free magnesium, ATP and blebbing during chemical hypoxia in cultured rat hepatocytes.

Cytosolic free Mg2+ concentration was determined in 1-day cultured rat hepatocytes using Multiparameter Digitized Video Microscopy (MDVM) of the fluorescent probe, mag-fura-2. Chemical hypoxia with KCN (5 mM) and iodoacetate (1 mM), a model which mimics the ATP depletion and reductive stress of hypoxia, caused a rapid increase of free Mg2+ from 1.1 +/- 0.2 to 1.6 +/- 0.2 mM within 4 min. Concurrently, numerous small plasma membrane blebs formed and ATP levels dropped from 13.24 to 1.32 nmol/10(6) cells. Removal of KCN and iodoacetate resulted in recovery of ATP to 60-70% of pre-exposure levels, a concomitant decrease in cytosolic free Mg2+ back toward basal levels, and reversal of blebbing (bleb resorption). These results indicate that changes of cytosolic free Mg2+ inversely reflect changes of ATP in a model of hypoxia and reoxygenation. Bleb formation and resorption were dependent on the fall and rise of ATP.

Adenosine Triphosphate↗
PubMed1990

Protection by acidotic pH and fructose against lethal injury to rat hepatocytes from mitochondrial inhibitors, ionophores and oxidant chemicals.

The importance of mitochondrial ATP formation and extracellular acidosis was evaluated in hepatocyte suspensions after different toxic treatments. Acidotic pH was protective against cell killing from all toxic treatments examined except for pronase, a toxic protease. Fructose, a substrate for glycolytic ATP formation, provided good protection against toxicity from cyanide, oligomycin, t-butyl hydroperoxide, menadione and cystamine. Protection by fructose against CCCP, gramicidin and Br-A23187 required oligomycin. This indicated that these ionophores were causing cytotoxicity by uncoupling oxidative phosphorylation. Fructose provided little protection against pronase and HgCl2, the latter compound being a potent inhibitor of glycolysis. In conclusion, disruption of mitochondrial ATP formation was a common event contributing to the toxicity of chemical oxidants and ionophores. Acidotic pH was generally protective under these conditions of impaired ATP generation.

Animals↗
PubMed1990

Toxic injury from mercuric chloride in rat hepatocytes.

The relationship between cytosolic free Ca2+, mitochondrial membrane potential, ATP depletion, pyridine nucleotide fluorescence, cell surface blebbing, and cell death was evaluated in rat hepatocytes exposed to HgCl2. In cell suspensions, 50 microM HgCl2 oxidized pyridine nucleotides between 1/2 and 2 min, caused ATP depletion between 2 and 5 min, and produced an 89% loss of cell viability after 20 min. Rates of cell killing were identical in high (1.2 mM) and low (2.6 microM) Ca2+ buffers. Cytosolic free Ca2+ was determined in 1-day cultured hepatocytes by ratio imaging of Fura-2 employing multiparameter digitized video microscopy. In high Ca2+ medium, HgCl2 caused a 3-4-fold increase of free Ca2+ beginning after 6-7 min, but free Ca2+ did not change in low Ca2+ medium. Bleb formation occurred after about 4-5 min in both buffers prior to any increase of free Ca2+. Subsequently, in high Ca2+ medium, blebs became hot spots of free Ca2+ (greater than 600 nM). After about 2 min of exposure to HgCl2, rhodamine 123 fluorescence redistributed from mitochondrial to cytosolic compartments signifying collapse of the mitochondrial membrane potential. The results taken together demonstrate that bleb formation, ATP depletion, and the onset of cell death are not dependent on an increase of cytosolic free Ca2+. HgCl2 toxicity appears to be a consequence of inhibition of oxidative phosphorylation leading to ATP depletion and cell death.

Adenosine Triphosphate↗
PubMed1990

Lack of metabolic effects of cholecystokinin on hepatocytes.

We previously reported that the liver was the major organ that extracts small, biologically active, circulating forms of cholecystokinin. Although our work indicated extensive degradation of cholecystokinin extracted from plasma during its transit across the hepatocyte, it was unclear whether cholecystokinin might also have a physiological effect on this cell before its intracellular degradation. Therefore we tested the hypothesis that cholecystokinin has a direct biological effect on hepatocytes. Using freshly isolated or cultured hepatocytes, we studied whether cholecystokinin-octapeptide alters protein synthesis, affects amino acid transport or influences cytosolic free calcium concentrations. Using liver slices, we also determined the effect of cholecystokinin-octapeptide on cyclic nucleotide levels. Cholecystokinin-octapeptide, up to a concentration of 1 mumol/L, had no effect on the incorporation of radiolabeled amino acids into total hepatocyte protein; in contrast, comparable molar amounts of insulin stimulated protein synthesis by as much as 37% (ED50 = 1.5 x 10(-10) mol/L). Although insulin and glucagon stimulated the transport into hepatocytes of 14C-alpha-aminoisobutyric acid, a nonmetabolizable amino acid analog, cholecystokinin-octapeptide had no affect Cholecystokinin-octapeptide also did not affect either the concentration of calcium in individual hepatocytes, as measured by digitized video microscopy using Fura-2, or the levels of cyclic AMP or cyclic GMP in liver slices. Our results show that cholecystokinin has no effect on protein synthesis, on amino acid transport or on hepatocyte calcium and cyclic nucleotide levels. These and our previous data suggest that the primary outcome of hepatic extraction of cholecystokinin is hormone degradation.

Amino Acids↗
PubMed1990

Interrelationships of platelet-derived growth factor isoform-induced changes in c-fos expression, intracellular free calcium, and mitogenesis.

Both increases in c-fos proto-oncogene expression and intracellular free calcium ([Ca2+]i) have been implicated as necessary components of the signal transduction pathway by which platelet-derived growth factor (PDGF) stimulates DNA synthesis in cultured BALB/c3T3 fibroblasts. To determine the interrelationship between PDGF-induced increases in c-fos proto-oncogene expression and [Ca2+]i, purified, recombinant BB and AA homodimeric isoforms of PDGF were used to evaluate the dose-response relationships and mechanisms of growth factor-induced changes in these two parameters as well as DNA synthesis. Concentration-dependent increases in [Ca2+]i, c-fos expression, and [3H]thymidine incorporation were observed with both BB and AA PDGF isoforms. BB PDGF was consistently more potent and efficacious than the AA isoform in eliciting a given response. The [Ca2+]i dependency of PDGF-induced increases in c-fos expression and DNA synthesis was determined by pretreatment of cells with agents that inhibit increases in [Ca2+]i: BAPTA, Quin-2, and TMB-8. Under these conditions, PDGF-induced DNA synthesis was blocked, whereas c-fos expression was enhanced. Conversely, in cells made deficient in protein kinase C (PKC) activity by prolonged treatment with phorbol ester, BB and AA PDGF-induced c-fos expression was inhibited by 75-80%, while PDGF-induced increases in [Ca2+]i and DNA synthesis were unaffected or enhanced. Additionally, the PKC-independent component of PDGF-stimulated c-fos expression was found to be independent of increases in [Ca2+]i. These data suggest that 1) both BB and AA PDGF isoforms elicit alterations in [Ca2+]i and c-fos proto-oncogene expression through the same or similar mechanisms in BALB/c3T3 fibroblasts, 2) PDGF-stimulated increases in [Ca2+]i are not required for c-fos expression, and 3) distinct pathways regulate PDGF-induced c-fos expression and mitogenesis, with c-fos expression being substantially PKC-dependent yet [Ca2+]i-independent, while mitogenesis is [Ca2+]i-dependent yet PKC-independent.

Animals↗
PubMed1990

Relationship of social class characteristics and risk factors for coronary heart disease in West Germany.

A cross-sectional analysis of the baseline survey of the German Cardiovascular Prevention Study was carried out to analyse the relationship between four different social class characteristics and major risk factors for coronary heart disease. 4,796 randomly selected German residents aged 25-69 years participated in the health survey between 1984 and 1986. The response rate was 66.2%. No significant association with social class variables was observed for prevalence of hypertension, hypercholesterolaemia or low high density lipoproteins. Multiple logistic regression analysis showed that obesity and lack of physical activity were significantly more prevalent in lower social classes for both sexes, while for cigarette smoking this relationship held for males only. The strongest social class gradient was found for lack of physical activity, adjusted odds ratio 4.75, P less than 0.001, comparing lowest social class by composite index to highest. The number of coronary heart disease risk factors per study subject increased strongly with decreasing social class. Education, measured as years of schooling, showed a stronger association with coronary heart disease risk factors than household income, occupational status, or a three-dimensional composite index of social class. These findings indicate the need to focus on lower social class population groups when carrying out community-based coronary heart disease primary prevention programmes, particularly with regard to smoking, obesity, and lack of physical activity.

Adult↗
PubMed1990

Characterization of low-light-level cameras for digitized video microscopy.

The use of low-light-level video cameras and solid-state image detectors in conjunction with image digitizers for optical microscopy is increasing dramatically as more people learn about such systems, and as they become more powerful, less expensive, and easier to use. However, there is currently little information available allowing comparison between cameras, or for determining camera suitability for a given experiment. In this paper, we describe a series of tests designed to characterize the performance of low-light-level cameras. The results of these tests should assist in the selection of appropriate cameras for given video microscopy applications.

Image Processing, Computer-Assisted↗
PubMed1990

Angiotensin II stimulates protein-tyrosine phosphorylation in a calcium-dependent manner.

Cellular responses to epidermal growth factor (EGF) are dependent on the tyrosine-specific protein kinase activity of the cell-surface EGF receptor. Previous studies using WB rat liver epithelial cells have detected at least 10 proteins whose phosphotyrosine (P-Tyr) content is increased by EGF. In this study, we have examined alternate modes of activating tyrosine phosphorylation. Treatment of WB cells with hormones linked to Ca2+ mobilization and protein kinase C (PKC) activation, including angiotensin II, [Arg8]vasopressin, or epinephrine, stimulated rapid (less than or equal to 15-s) and transient increases in the P-Tyr content of several proteins (p120/125, p75/78, and p66). These proteins, detected by anti-P-Tyr immunoblotting, were similar in molecular weight to a subset of EGF-sensitive P-Tyr-containing proteins (P-Tyr-proteins). The increased P-Tyr content was confirmed by [32P]phosphoamino acid analysis of proteins recovered by anti-P-Tyr immunoprecipitation. Elevating intracellular [Ca2+] with the ionophore A23187 or ionomycin or with the tumor promoter thapsigargin mimicked the effects of hormones on tyrosine phosphorylation, whereas treatment with a PKC-activating phorbol ester did not. In addition, responses to angiotensin II were not diminished in PKC-depleted cells. Ca2+ mobilization, measured by fura-2 fluorescence, was coincident with the increase in tyrosine phosphorylation in response to angiotensin II or thapsigargin. Loading cells with the intracellular Ca2+ chelator bis-(o-aminophenoxy)ethane-N ,N ,N' , N'-tetraacetic acid (BAPTA) inhibited the appearance of all P-Tyr-proteins in response to angiotensin II, thapsigargin, or ionophores, as well as two EGF-stimulated P-Tyr-proteins. The majority of EGF-stimulated P-Tyr-proteins were not affected by BAPTA. These studies indicate that angiotensin II can alter protein-tyrosine phosphorylation in a manner that is secondary to, and apparently dependent on, Ca2+ mobilization. Thus, ligands such as EGF and angiotensin II, which act through distinct types of receptors, may activate secondary pathways involving tyrosine phosphorylation. These results also raise the possibility that certain growth-promoting effects of Ca2+ -mobilizing agents such as angiotensin II may be mediated via tyrosine phosphorylation.

Angiotensin II↗
PubMed1990

Multiparameter digitized video microscopy of toxic and hypoxic injury in single cells.

There is no clear picture of the critical events that lead to the transition from reversible to irreversible injury. Many studies have suggested that a rise in cytosolic free Ca2+ initiates plasma membrane bleb formation and a sequence of events that lead ultimately to cell death. In recent studies, we have measured changes in cytosolic free Ca2+, mitochondrial membrane potential, cytosolic pH, and cell surface blebbing in relation to the onset of irreversible injury and cell death following anoxic and toxic injury to single hepatocytes by using multiparameter digitized video microscopy (MDVM). MDVM is an emerging new technology that permits single living cells to be labeled with multiple probes whose fluorescence is responsive to specific cellular parameters of interest. Fluorescence images specific for each probe are collected over time, digitized, and stored. Image analysis and processing then permits quantitation of the spatial distribution of the various parameters with the single living cells. Our results indicate the following: The formation of plasma membrane blebs accompanies all types of injury in hepatocytes. Cell death is a rapid event initiated by rupture of a plasma membrane bleb, and it is coincident with the onset of irreversible injury. An increase of cytosolic free Ca2+ is not the stimulus for bleb formation or the final common pathway leading to cell death. A decrease of mitochondrial membrane potential precedes the loss of cell viability. Cytosolic pH falls by more than 1 pH unit during chemical hypoxia. This acidosis protects against the onset of cell death.

Animals↗
PubMed1990

R- and S-wave amplitude changes with acute anterior transmural myocardial ischemia. Correlations with left ventricular filling pressures.

The value of R- and S-wave amplitude changes as electrocardiographic (ECG) markers of myocardial ischemia and dysfunction was evaluated using coronary angioplasty as a model of acute transmural ischemia and ST segment elevation. Hemodynamic data and 12-lead ECGs were recorded at baseline and during coronary occlusion in 34 patients with left anterior descending artery angioplasty. In the precordial leads V1 through V4, the sum of R-wave amplitude increased in 17 patients, was unchanged in ten, and decreased in seven; the sum of S-wave amplitude decreased in 33 patients (including two patients with complete loss of S wave) and increased in one. Mean R-wave change was 2.7 +/- 6.2 mm, mean S-wave change was -12.9 +/- 9.0 mm, and mean precordial ST elevation was 12.5 +/- 8.7 mm. Absolute R-wave change correlated directly with ST elevations (p = .013), while S-wave change correlated inversely (p less than .007). Only ST elevations correlated with changes in pulmonary capillary wedge pressure (PW) (p less than .007). In the precordial lead with maximum ST elevations, only R-wave changes correlated with ST elevations (p = .002), and both R-wave changes and ST elevations correlated with changes in PW (R:p = .027; ST:p = .007). The presence of large increases in R waves or decreases in S wave, or of high-magnitude ST elevations identified patients with the highest elevations in PW. In conclusion, decreases in S waves and, less commonly, increases in R waves are seen with diagnostic ST elevations and may have some limited clinical value. The correlation between magnitude of acute anterior ST elevations and changes in left ventricular filling pressures may have important clinical consequence.

Acute Disease↗
PubMed1990

Calcium and pH in anoxic and toxic injury.

The critical events that lead to the transition from reversible to irreversible injury remain unclear. Studies are reviewed that have suggested that a rise in cytosolic free Ca2+ initiates plasma membrane bleb formation and a sequence of events that leads ultimately to cell death. In recent studies, we have measured changes in cytosolic free Ca2+, mitochondrial membrane potential, cytosolic pH, and cell surface blebbing in relation to the onset of irreversible injury and cell death following anoxic and toxic injury to single hepatocytes utilizing multiparameter digitized video microscopy (MDVM). MDVM is an emerging new technology that permits single living cells to be labeled with multiple probes whose fluorescence is responsive to specific cellular parameters of interest. Fluorescence images specific for each probe are collected over time, and then digitized and stored. Image analysis and processing then permits quantitation of the spatial distribution of the various parameters within the single living cells. Our results indicate the following: (1) formation of plasma membrane blebs accompanies all types of injury in hepatocytes; (2) cell death is a rapid event, initiated by rupture of a plasma membrane bleb, and is coincident with the onset of irreversible injury; (3) an increase of cytosolic free Ca2+ is not the stimulus for bleb formation or the final common pathway leading to cell death; (4) a decrease of mitochondrial membrane potential precedes loss of cell viability; (5) cytosolic pH falls by more than 1 pH unit during chemical hypoxia. This acidosis protects against the onset of cell death.

Animals↗
PubMed1990

Variation in coronary risk factor levels of men and women between the German-speaking MONICA centres.

The aim of this analysis was to compare levels of risk factors for coronary heart disease (CHD) in men and women aged 25-64 years between German-speaking MONICA collaborating centres, the German Democratic Republic (GDR), Augsburg - the Federal Republic of Germany (FRG)(Au), Bremen - FRG (Br), Heidelberg - FRG (He), and Vaud/Fribourg - Switzerland (CH, with a German-speaking minority). Prevalence of cigarette smoking in men showed little variation in four centres (34 to 40%) and was higher in BR men (49%), while it varied from 17% (GDR) to 33% (BR) in women. Mean total serum cholesterol values (mmol/L) were highest in GDR and CH men (both 6.2) and GDR women (6.1), and lowest in both He men (5.7) and He women (5.6). The proportion with cholesterol values greater than or equal to 6.7 mmol/L was largest in CH men (34%) and smallest in FRG (He) women (17%), while lowering the cut-off point from 6.7 to 6.5 mmol/L raised the prevalence of hypercholesterolaemia in all centres by 5 to 10%. Mean values (mmHg) of blood pressure (BP) were highest in both GDR men (140/88) and women (138/86), as was the prevalence of hypertensive BP values. In all centres, women aged 25-34 had BP values approximately 12/5 mmHg lower than age-matched men, but BP values similar to men at age 55-64, which indicates that age-parallel increase in BP was steeper in women than men.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Role of Na+/H+ exchange by interferon-gamma in enhanced expression of JE and I-A beta genes.

The rapid transductional sequences initiated by interferon-gamma (IFN-gamma) on binding to its receptor regulate functional and genomic responses in many cells but are not well defined. Induction of macrophage activation is an example of such functional and genomic changes in response to IFN-gamma. Addition of IFN-gamma to murine macrophages, at activating concentrations, produced rapid (within 60 seconds) alkalinization of the cytosol and a concomitant, rapid influx of 22Na+. Amiloride inhibited the ion fluxes and the accumulation of specific messenger RNA for two genes induced by IFN-gamma (the early gene JE and the beta chain of the class II major histocompatibility complex gene I-A). The data indicate that IFN-gamma initiates rapid exchange of Na+ and H+ by means of the Na+/H+ antiporter and that these amiloride-sensitive ion fluxes are important to some of the genomic effects of IFN-gamma.

Amiloride↗
PubMed1989

The TGF-alpha precursor expressed on the cell surface binds to the EGF receptor on adjacent cells, leading to signal transduction.

The 50 amino acid form of TGF-alpha is cleaved from a conserved integral membrane glycoprotein by a protease that, in many tumor cells, appears to be limiting. To test whether the membrane-bound precursor has biological activity in the absence of processing, we introduced amino acid substitutions at the proteolytic cleavage sites. BHK cells transfected with expression vectors containing these altered sequences do not secrete detectable levels of mature TGF-alpha into the medium, but express high levels of proTGF-alpha at the cell surface. Coincubation of these BHK cells with A431 cells demonstrates that membrane-bound proTGF-alpha may bind to EGF receptors on the surface of contiguous cells, induce receptor autophosphorylation, and thereby produce a rapid rise in A431 intracellular calcium levels. Thus, proTGF-alpha can be biologically active in the absence of processing, a fact that may have implications for the integral membrane precursors of related growth factors.

Amino Acid Sequence↗