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Biomedical subjects

R Heinrich

Publications and source records attributed to R Heinrich.

191 records · Page 11Linked to original sources
PubMedDate not supplied

Tissue-PO2 (PGO2) in the carotid body of the cat and tidal volume (V) during normovolaemic haemodilution.

During normovolaemic haemodilution with Macrodex (R), the basic respiratory activity is unchanged, while the ventilatory responses to hypoxia and hypercapnia generally decrease. The PGO2 in the cat carotid body remains constant down to an Hk of 10% to 15% and then decreases. This confirms the suggestion of Acker and Lübbers (1976) that increased plasma flow through the carotid body does not influence the oxygen supply to this organ, despite variations of both oxygen transport capacity and haemoglobin concentration. The fine structure of the carotid body is partly destroyed by haemodilution with Macrodex (R) and this could account for the impaired chemoreception.

Animals↗
PubMedDate not supplied

Aminergic neuron systems of lobsters: morphology and electrophysiology of octopamine-containing neurosecretory cells.

In the American lobster (Homarus americanus) the biogenic amines serotonin and octopamine appear to play important and opposite roles in the regulation of aggressive behavior, in the establishment and/or maintenance of dominant and subordinate behavioral states and in the modulation of the associated postural stances and escape responses. The octopamine-containing neurosecretory neurons in the thoracic regions of the lobster ventral nerve cord fall into two morphological subgroups, the root octopamine cells, a classical neurohemal group with release regions along second thoracic roots, and the claw octopamine cells, a group that selectively innervates the claws. Cells of both subgroups have additional sets of endings within neuropil regions of ganglia of the ventral nerve cord. Octopamine neurosecretory neurons generally are silent, but when spontaneously active or when activated, they show large overshooting action potentials with prominent after-hyperpolarizations. Autoinhibition after high-frequency firing, which is also seen in other crustacean neurosecretory cells, is readily apparent in these cells. The cells show no spontaneous synaptic activity, but appear to be excited by a unitary source. Stimulation of lateral or medial giant axons, which excite serotonergic cells yielded no response in octopaminergic neurosecretory cells and no evidence for direct interactions between pairs of octopamine neurons, or between the octopaminergic and the serotonergic sets of neurosecretory neurons was found.

Animals↗
PubMedDate not supplied

The modelling of metabolic systems. Structure, control and optimality.

This article gives an overview of recent developments in the modelling of the structure, control and optimality of metabolic networks. In particular, methods of algebraically analysing the topology of such networks are presented. By these methods, conservation relations and elementary modes of functioning (biochemical routes) can be detected. The principles of metabolic control analysis are outlined. Various recent extensions of this theory are presented, such as an analysis in terms of time dependent variables and modular analysis. Evolutionary optimisation principles are applied to explain the catalytic efficiency of single enzymes as well as the structural design of metabolic pathways. Special results concern the optimal distribution of ATP consuming and ATP producing reactions in glycolysis.

Catalysis↗
PubMedDate not supplied

Metabolic pathway analysis: basic concepts and scientific applications in the post-genomic era.

This article reviews the relatively short history of metabolic pathway analysis. Computer-aided algorithms for the synthesis of metabolic pathways are discussed. Important algebraic concepts used in pathway analysis, such as null space and convex cone, are explained. It is demonstrated how these concepts can be translated into meaningful metabolic concepts. For example, it is shown that the simplest vectors spanning the region of all admissible fluxes in stationary states, for which the term elementary flux modes was coined, correspond to fundamental pathways in the system. The concepts are illustrated with the help of a reaction scheme representing the glyoxylate cycle and adjacent reactions of aspartate and glutamate synthesis. The interrelations between pathway analysis and metabolic control theory are outlined. Promising applications for genome annotation and for biotechnological purposes are discussed. Armed with a better understanding of the architecture of cellular metabolism and the enormous amount of genomic data available today, biochemists and biotechnologists will be able to draw the entire metabolic map of a cell and redesign it by rational and directed metabolic engineering.

Biotechnology↗
PubMedDate not supplied

Compensating lipid fluxes generated by the aminophospholipid translocase.

By a combined kinetic and thermodynamic model on the transbilayer dynamics and asymmetric distribution of lipids in the red blood cell, compensating lipid fluxes to the exoplasmic leaflet have been analysed, counterbalancing the active transport of aminophospholipids to the cytoplasmic monolayer by the aminophospholipid translocase. The compensating fluxes are assumed to be of passive nature generated by forces of lateral mechanical stress and of lipid concentration differences between the two monolayers. These forces are shown to be caused and maintained by the operation of the aminophospholipid translocase. Simulations reveal that a reduction of the compensating fluxes upon ATP-depletion can be attributed to the inhibition of the aminophospholipid translocase. Thus, a Mg(2+)- and ATP-dependence of the outward movement of phospholipid analogues in the plasma membrane of red blood cells can be expected independent of the existence and operation of an ATP-dependent 'floppase' activity.

Adenosine Triphosphate↗
PubMedDate not supplied

Elevated muscle tissue oxygen tension in short-term insulin-dependent diabetes mellitus.

In order to assess hemodynamic changes in early phases of insulin-dependent diabetes mellitus, muscle tissue oxygen tensions were determined in 7 newly diagnosed insulin-dependent diabetic patients and in 6 healthy control subjects matched for sex, age and weight. Muscle tissue oxygen tension was measured by polarrographic needle probes while breathing ambient air and oxygen enriched air with an oxygen concentration of 40 per cent as well. Three times during the experiment, heart rates, blood pressures, blood glucose concentrations, and capillary oxygen tensions were obtained. Heart rate, blood pressure, peripheral and autonomic nerve functions did not differ between the 2 groups studied. While breathing ambient air, muscle tissue oxygen tensions were significantly (p = 0.025) higher in the diabetic patients than in the control subjects. In contrast to the control subjects, diabetic patients did not increase muscle tissue oxygen tensions after inhalation of oxygen enriched air despite of an equal increase in capillary oxygen tensions (2p less than 0.05). Local tissue hypoxia does not seem to be a leading cause of hemodynamic abnormalities in the early phases of diabetes.

Adult↗