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Biomedical subjects

U Wick

Publications and source records attributed to U Wick.

10 recordsLinked to original sources
PubMed1990

[Analysis of alpha 1-antitrypsin deficiency using DNA methods].

Deficiency of alpha 1-antitrypsin can be diagnosed by DNA methods that are quick and also give reproducible results. Direct DNA analysis of the M, S, and Z alleles of the alpha 1-antitrypsin gene is possible when two molecular biology techniques are combined: a part of the gene is enzymatically replicated according to the pattern of the human DNA that is to be investigated. On hybridization with the various allele-specific pieces of synthetic DNA the copies that have come about in this way give a signal corresponding to the genotype. Only a small amount of material (0.5 microgram DNA) is needed for the investigation. This method is thus suitable for prenatal diagnosis when this is requested by members of a family known to be affected. A total of 53 samples were typed and investigations were carried out in six families.

Alleles↗
PubMed1979

Oscillations of cyclic nucleotide concentrations in relation to the excitability of Dictyostelium cells.

Aggregating cells of Dictyostelium discoideum are able to release cyclic AMP periodically. The oscillations of cAMP generation are associated with changes in adenylate cyclase activity. Cyclic AMP receptors on the cell surface are functionally coupled to the oscillating system as evidenced by phase shifts that are induced by small pulses of extracellular cAMP. An important element of the oscillating system is the signal processing from surface receptors to the adenylate cyclase. This pathway exhibits adaptation resulting in the suppression of responses to constant, elevated concentrations of cAMP. The signal input for adenylate cyclase activation is, therefore, a change in the extracellular cAMP concentration with time. Oscillations in the absence of detectable changes of intra- or extracellular cAMP concentrations suggest the possibility that there is a metabolic network in D. discoideum cells that undergoes oscillations without coupling to adenylate cyclase. Cyclic GMP concentrations oscillate with a slight phase difference in advance of that of cAMP, suggesting that the two nucleotide cyclases might not be activated by the same mechanism. Elevation of extracellular calcium exerts an inhibitory effect on the accumulation of cAMP and on the second of the two cGMP peaks.

Adenylyl Cyclases↗
PubMed1978

Cyclic-AMP stimulated calcium influx into aggregating cells of Dictyostelium discoideum.

Within about 10 seconds after stimulation of Dictyostelium discoideum cells with cyclic AMP an increased rate of 45Ca influx was observed. Part of the cellular calcium reappeared in the extra-cellular medium between 1 and 3 minutes after stimulation. No effect of 5'AMP on calcium distribution was found. The transient calcium influx is discussed in connection with chemotaxis and other cyclic-AMP induced responses.

Calcium↗
PubMed1975

Cell communication by periodic cyclic-AMP pulses.

At the surface of aggregating cells of the slime mould, Dictyostelium discoideum, two different sites interacting with extracellular cAMP are detectable: binding sites and cycl-nucleotide phosphodiesterase. Both sites are developmentally regulated. An adequate stimulus for the chemoreceptor system in D. discoideum is the change of cAMP concentration in time, rather than concentration per se: long-term binding of cAMP causes only short-term response. The system is, consequently, adapted to the recognition of pulses rather than to steady-state concentrations of cAMP. The ce,lls are, nevertheless, able to sense stationary spatial gradients and to respond to them by chemotactic orientation. The possibility is discussed that they do so by transforming spatial concentration changes into temporal ones, using extending pseudopods as sensors. The cAMP recognition system is part of a molecular network involved in the generation of spatio-temporal patterns of cellular activities. This system controls the periodic formation of chemotactic signals and their propagation from cell to cell. The phosphodiesterase limits the duration of the cAMP pulses and thus sharply separates the periods of signalling; the binding sites at the cell surface are supposed to be the chemoreceptors. The control of cellular activities via cAMP receptors can be studied with biochemical techniques with cell suspensions in which spatial inhomogeneities are suppressed by intense stirring, whereas the temporal aspect of the spatiotemporal pattern is preserved. Under these conditions it can be shown that the extracellular cAMP concentration changes periodically, and that the phase of the cellular oscillator can be shifted by external pulses of cAMP. It can also be shown that small cAMP pulses induce a high output of cAMP, which demonstrates signal amplification, a function necessary for a cellular relay system.

3',5'-Cyclic-AMP Phosphodiesterases↗