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Biomedical subjects

U Walter

Publications and source records attributed to U Walter.

At least 199 records · Page 11Linked to original sources
PubMed1982

Studies on erythrocyte acetylcholinesterase in essential hypertension.

There is accumulating evidence that acetylcholinesterase (AChE might be involved in the transport of sodium across biological membranes. Consequently, because in primary hypertension abnormalities in the transport of sodium by red blood cells have been documented. AChE activities were measured in hemoglobin-free red-blood-cell membranes of patients with essential hypertension. In the absence of any effectors, the Michaelis constant of AChE for acetylcholine (Km) was 1.57 . 10(-5) mol/l, both in normotensives and in hypertensives. Sodium inhibited AChE at low substrate concentrations, whereas the enzyme was activated by sodium at moderate and high substrate levels. With increasing sodium, the substrate optimum was displaced toward higher substrate concentration. On the other hand, an inhibition of AChE by excess substrate could be demonstrated. Erythrocyte AChE activity of male patients with essential hypertension was no different from that of the normotensive controls. Therefore, abnormalities in electrolyte transport mechanisms reported in essential hypertension might be independent of AChE activity.

Acetylcholinesterase↗
PubMed1982

[ATPase activity and sodium transport in erythrocytes of patients with essential hypertension (author's transl)].

The rate constant for erythrocyte "total" sodium efflux was significantly decreased in patients with essential hypertension compared with normotensive controls due to a reduced "ouabain-sensitive" (active) sodium transport. The rate constants for "ouabain-insensitive", "ouabain-insensitive furosemide-sensitive" and "ouabain-insensitive furosemide-insensitive" sodium efflux were not different between hypertensives and normotensives. Ouabain inhibited sodium efflux by 74% and furosemide by a further 13%, both in hypertensives and in normotensives. The reduced rate constant for active erythrocyte transport in patients with essential hypertension was due to a diminished Na-K-ATPase activity demonstrable in hemolyzed and dialyzed erythrocytes. In contrast, in hemoglobin-free red blood cell membranes Na-K-ATPase activity was not different between both groups. Apparently the centrifugation procedure, which is necessary for preparation of hemoglobin-free membranes, leads to a loss of non-hemoglobin proteins, including ouabain-sensitive and ouabain-insensitive ATPase and/or a Na-K-ATPase inhibiting factor. Thus, the results obtained in hemolyzed and dialyzed red blood cells reflect probably better the conditions in the intact erythrocyte than do measurements on hemoglobin-free membranes, suggesting a decreased Na-K-ATPase activity in erythrocytes of essential hypertensives. However, the diminished rate constant for ouabain-sensitive sodium efflux did not result in a measurable increase in erythrocyte sodium indicating that this biochemical abnormality can fully be compensated in moderate essential hypertension without excess salt intake. The cause of the reduced rate constant for ouabain-sensitive sodium efflux is not clear. However, as suggested for sodium-potassium cotransport and for sodium-lithium countertransport it might be determined genetically.

Adenosine Triphosphatases↗
PubMed1982

Frozen tissue sections as an experimental system to reveal specific binding sites for the regulatory subunit of type II cAMP-dependent protein kinase in neurons.

Specific binding sites for the regulatory subunit of type II cAMP-dependent protein kinase (RII) were revealed in neurons by an immunohistochemical approach. Fixed frozen sections of several regions of the rat central nervous system were incubated in the presence of bovine RII. Bound bovine RII was subsequently detected by an immunofluorescence procedure using antibodies that recognize bovine but not rat RII. The results indicate that RII binds with high affinity to neurons. Binding is prominent in dendrites and almost undetectable in axons and axon terminals. The morphological distribution of the RII binding sites is almost identical to that of microtubule-associated protein 2 (MAP 2) immunoreactivity. Preadsorption of RII with a MAP preparation highly enriched in MAP 2 completely abolished binding of RII to tissue sections, suggesting that the binding is mediated by MAP 2. Our results indicate that frozen sections of fixed tissues are a suitable experimental system for study of specific interactions of cellular macromolecules at a morphological level.

Animals↗
PubMed1981

Inhibition of molybdenum blue formation by ATP.

Molybdenum blue formation was not affected by the presence of ATP up to a concentration of 1.2 muM/l. At higher concentrations the color development was inhibited relative to ATP concentration, finally reaching complete inhibition. Auto-hydrolysis of ATP was found at a rate of 1.4%/h. An exact determination of inorganic phosphate in the presence of easily hydrolyzed phosphate esters requires the measurement of extinction at fixed time intervals and extrapolation back to time zero.

Adenosine Triphosphate↗
PubMed1981

Red blood cell sodium and potassium after hydrochlorothiazide.

In six of seven healthy males 6 days of hydrochlorothiazide (HCT), 50 mg twice daily, without potassium supplements resulted in a rise in red blood cell (RBC) sodium concentration. Serum potassium concentration fell in all subjects. Four days after discontinuing HCT, intracellular sodium and extracellular potassium concentrations had normalized. Throughout the evaluation period the course of mean relative intracellular sodium was almost a mirror image of mean relative extracellular potassium. Thus, either the decline of serum potassium or of HCT (because of its inhibitory effect on Na-K-ATPase activity) might have diminished Na-K-ATPase-dependent active RBC sodium efflux with a resultant rise in erythrocyte sodium concentration. RBC potassium and serum sodium concentrations were not affected by short-term exposure to HCT.

Erythrocytes↗
PubMed1981

Effect of ouabain and furosemide on erythrocyte sodium and phosphate transport.

The effects of ouabain and furosemide on the unidirectional efflux of sodium and phosphate ions were studied in freshly drawn human red blood cells (RBCs). In the presence of physiologic concentrations of sodium and potassium the rate of sodium efflux was reduced by 74% due to ouabain sensitivity. Furosemide (1.0 mmol/l) reduced ouabain-insensitive sodium transport rate by a further 50%. Thus, 13% of total sodium efflux was inhibited by furosemide when ouabain was present. In the absence of ouabain, however, furosemide inhibited 31% of total sodium transport, indicating that it also affected ouabain-sensitive sodium efflux. Phosphate transfer of RBCs was almost 1.0 mmol/l RBCs per hour. Erythrocyte concentration of orthophosphate, however, was only 0.59 mmol/l RBCs. Organic phosphate esters must therefore have been cleaved to maintain constant phosphate elimination. The hydrolysis of adenosine triphosphate (ATP) by Na-K-ATPase might be involved because the phosphate transfer of almost 0.12 mmol/l RBCs per hour was ouabain sensitive. Furosemide reduced phosphate efflux by 50% due to reduction in passive permeability of the RBC membrane. Additional inhibition of any phosphate ester hydrolyzing enzymatic activity cannot, however, by excluded.

Adult↗
PubMed1981

Immunohistochemical localization of cyclic GMP-dependent protein kinase in mammalian brain.

The distribution of cyclic GMP-dependent protein kinase in rat brain has been studied by an immunological approach involving radioimmunoassay and fluorescence immunohistochemistry. Data obtained by radioimmunoassay indicate that cyclic GMP-dependent protein kinase is 20- to 40-fold more concentrated in cerebellum than in other brain regions. Immunohistochemical experiments demonstrate that the high concentration of immunoreactivity of the protein kinase in cerebellum is attributable to Purkinje cells. Immunoreactivity in these cells is homogeneously distributed throughout the cell (perikarya, dendrites, and axons) with the exception of the nucleus. No other neurons either in the cerebellum or in other brain regions were stained by antiserum to the protein kinase. Immunoreactivity, however, was found throughout the brain on smooth muscle cells of blood vessels.

Animals↗
PubMed1981

Steroid hormones may regulate autophosphorylation of adenosine-3',5'-monophosphate-dependent protein kinase in target tissues.

A protein in rat liver cytosol whose phosphorylation was regulated by hydrocortisone administration in vivo was tentatively identified as the regulatory subunit of a cAMP-dependent protein kinase. Evidence that this protein, whose phosphorylation was regulated by steroid and cyclic AMP, is the regulatory subunit of type-II cAMP-dependent protein kinase included: (a) co-purification of the steroid/cAMP-regulated protein and the regulatory subunit during DEAE-cellulose, Sepharose 4B, and hydroxylapatite column chromatography, (b) co-migration of the two proteins on dodecyl sulfate/polyacrylamide slab gels during the various steps of purification, (c) specific adsorption of the two proteins onto 8(6-aminohexylamino)-cAMP--Sepharose 4B, and (d) a similar pattern of distribution of the two proteins in various subcellular fractions prepared from rat liver homogenate. By each of these criteria, it was found that the steroid/cAMP-regulated protein present in rat liver cytosol behaved identically with the regulatory subunit of type-II cAMP-dependent protein kinase in that tissue. Results qualitatively similar to those obtained in the study of the effect of hydrocortisone on rat liver were also obtained in studies of the effects of other steroid hormones on other target tissues in the rat, including uterus (17 beta-estradiol), ventral prostate and seminal vesicle (testosterone), and epididymal fat pad (hydrocortisone). The tentative identification of the steroid/cAMP-regulated protein as the regulatory subunit of the type-II cAMP-dependent protein kinase in the cytosol of several tissues indicates that autophosphorylation of the regulatory subunit of type-II protein kinase may be regulated by the steroid hormones. The fact that three different classes of steroid hormones appear to affect the phosphorylation of the regulatory subunit of type-II cAMP-dependent protein kinase in their target tissues raises the possibility that this common biochemical action may play an important role in the mechanism of steroid hormone action. It is also possible that this effect of the steroid hormones may provide a molecular basis for some of the known physiological interactions of the steroid hormones with those hormones that act through using cAMP as a second messenger.

Adrenalectomy↗
PubMed1981

Distribution of cyclic-GMP-dependent protein kinase in various rat tissues and cell lines determined by a sensitive and specific radioimmunoassay.

Cyclic-GMP-dependent protein kinase purified from bovine lung was radioiodinated by the Bolton-Hunter procedure yielding a specific radioactivity of 2200 Ci/mmol of enzyme, Using a specific precipitating rabbit antiserum to the cyclic-GMP-dependent protein kinase, a sensitive radioimmunoassay was developed which can detect 200 pg (1.33 fmol) of cyclic GMP-dependent protein kinase. Immunoreactivity like that of cyclic-GMP-dependent protein kinase was detectable in extracts of all rat tissues tested, in extracts of cultured rat brain and heart cells, and in extracts of rat glioma (C6) and neuroblastoma x glioma hybrid cells. In extracts of several tissues and cell lines the presence of cyclic-GMP-dependent protein kinase was also demonstrated by a photoaffinity-labeling procedure using 8-azidoinosine 3',5'-[32P]monophosphate. The results suggest that cyclic-GMP-dependent protein kinase is ubiquitously distributed although its level varies significantly from tissue to tissue and cell type to type. The results also support the hypothesis that cyclic-GMP-dependent protein kinase is involved in mediating some of the intracellular effects of those hormones, neurotransmitters and drugs which regulate the intracellular level of cyclic GMP.

Animals↗
PubMed1980

Immunological distinction between guanosine 3':5'-monophosphate-dependent and adenosine 3':5'-monophosphate-dependent protein kinases.

A guanosine 3':5'-monophosphate (cGMP)-dependent protein kinase was purified from bovine lung using 8-(6-aminohexylamino)-cAMP-Sepharose. The activity of the purified enzyme was highly dependent on cGMP using histone f2b as a substrate. The self-phosphorylation of the purified enzyme was strongly inhibited by cGMP and not significantly affected by cAMP. A precipitating antiserum prepared in rabbits against the cGMP-dependent protein kinase specifically inhibited the histone kinase activity and the self-phosphorylation of the purified cGMP-dependent protein kinase without affecting the cGMP binding site. This antiserum also specifically inhibited the phosphorylation of the endogenous substrate proteins by endogenous cGMP-dependent protein kinase in smooth muscle membranes, but did not cross-react detectably with catalytic subunit or regulatory subunit of type I or type II cAMP-dependent protein kinase. Conversely, anti-sera against the regulatory subunit of type I or type II cAMP-dependent protein kinase did not cross-react detectably with cGMP-dependent protein kinase. The substantial differences between the immunological properties of the cGMP-dependent and cAMP-dependent protein kinases suggest that these two enzymes have distinct physiological roles.

Animals↗
PubMed1980

Microinjection of catalytic subunit of cyclic AMP-dependent protein kinase enhances calcium action potentials of bag cell neurons in cell culture.

We have found that the calcium action potentials of bag cell neurons from the abdominal ganglion of Aplysia may be enhanced by intracellular microinjection of the catalytic subunit of cyclic AMP-dependent protein kinase (ATP:protein phosphotransferase, EC 2.7.1.37). The catalytic subunit was purified from bovine heart and shown to be effective in stimulating the phosphorylation of bag cell proteins in homogenates at concentrations of 10-50 nM. Intracellular injection into isolated bag cell neurons maintained in primary culture was through pressure applied to microelectrodes filled at the tip with catalytic subunit (5-22 muM). In 11 of 16 injected cells, both the slope of the rising phase and the height of the action potentials evoked by a constant depolarizing current were markedly enhanced relative to the pre-injection control (mean increases, 73% and 35%, respectively). This effect could occur with no change in resting potential or in the latency of the action potential from the onset of the depolarizing pulse. The effect was observed with enzyme dissolved in three different salt solutions (Na phosphate, K phosphate, or KCl). In two experiments, tetrodotoxin (50 muM) added to the extracellular medium had no effect on the enhanced action potentials. Subsequent addition of the calcium antagonist Co(2+), however, diminished or abolished the spikes. In more than half of the experiments, the injection of catalytic subunit was accompanied by an increase in the input resistance of the cells as measured by applying small hyperpolarizing current pulses. In three experiments, subthreshold oscillations in membrane potential resulted from the injections. Control injections (24 cells), carried out either with carrier medium alone or with heat-inactivated enzyme preparations, did not produce spike enhancement, increased input resistance, or oscillations. Our data suggest that the stimulation of intracellular protein phosphorylation by the catalytic subunit of cyclic AMP-dependent protein kinase enhances the excitability of bag cell neurons by modifying calcium and potassium channels or currents.

Action Potentials↗
PubMed1980

[Massive upper gastrointestinal bleeding as first clinical manifestation of pseudoxanthoma elasticum (author's transl)].

We describe a patient with a "cryptogenic" massive upper gastrointestinal bleeding due to a pseudoxanthoma elasticum, recognized only postoperatively. She underwent twice emergency abdominal surgery with total gastrectomy and partial jejunal resection, with a complicated postoperative course. An insufficient enteral anastomosis was perhaps caused by deficient reapir mechanisms of the involved organs due to the underlying disease. Pseudoxanthoma elasticum, an hereditary degenerative disease of especially the elastic connective tissue, involves primarily the vascular system, skin, and eyes, with the typical complication of massive gastrointestinal bleedings. Instead of surgical intervention, such bleedings should be treated preferably by utmost application of conservative means.

Adult↗
PubMed1979

Presence of free cyclic AMP receptor protein and regulation of its level by cyclic AMP in neuroblastoma-glioma hybrid cells.

Neuroblastoma-glioma hybrid cells of line 108CC-5 were found to contain high levels of soluble adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase activity and high levels of two specific cAMP receptor proteins, RI and RII. Treatment of the hybrid cells with dibutyryl cAMP increased the level of RI but did not significantly affect the level either of RII or of cAMP-dependent protein kinase activity. The effect of dibutyryl cAMP could be mimicked by prostaglandin E1 and 3-isobutyl-1-methylxanthine, both of which are known to raise cAMP levels in neuroblastoma-glioma hybrid cells. Both in control as well as in dibutyryl cAMP-treated cells, RII but not RI was associated with cAMP-dependent protein kinase. Several lines of evidence suggest that RI represents the free regulatory subunit of type I cAMP-dependent protein kinase. The presence of this regulatory subunit as free cAMP receptor protein in neuroblastoma-glioma hybrid cells may be of significance with respect to the regulation of growth and differentiation in tumor cells.

Animals↗