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W Roos

Publications and source records attributed to W Roos.

8 recordsLinked to original sources
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↗
PubMed1979

[The pneumocephalus in cranio-cerebral trauma (author's transl)].

The accident surgeon is often surprised to see unusual intracranial translucencies on X-ray films of persons with skull injuries. Inexperienced physicians are often unable to immediately identify these translucencies as air enclosures in the intracranial cavity. Physicians not acquainted with pneumoencephalography commonly employed so far in neurological examinations will find it difficult to recognize in the accumulated air the contours of the ventricular, cerebral convolution and cisternal systems. Hence, the relatively rare event of air penetrating into the intracranial space as a result of an injury, is described here on the basis of two of our patients.

Accidents, Occupational↗
PubMed1977

Adenylyl cyclase and the control of cell differentiation in Dictyostelium dicoideum.

Adenylyl cyclase is part of a biochemical network that controls cell differentiation in Dictyostelium discoideum. At a certain stage of development the enzyme is rhythmically activated, with periods of about 8 min. These oscillations are superimposed upon an increase of the basal activity extending over a period of hours. The basal activity remains low in a mutant blocked at an early stage of development. In strain Ax-2 two periods of strongly increasing basal activity have been found: the first from 2 to 4 h after the end of the growth phase, the other beginning at about 8 h. Based on the periodic regulation of adenylyl cyclase, cyclic AMP is released into the extracellular space in the form of pulses. Application of cyclic-AMP pulses, but not its continuous influx, stimulates the increase of basal adenylyl cyclase activity. Two other constituents of the cyclic-AMP signal system cyclic-AMP receptors and cell-surface phosphodiesterase, are similarly controlled. The principal importance of positive feedback loops in a network controlling cell differentiation is discussed.

Adenylyl Cyclases↗