The circulatory physiopathology of human red blood cells investigated with a multiplatform model of cellular homeostasis. III. Senescence changes during the full circulatory lifespan

Human red blood cells (RBCs) have a circulatory lifespan of about four months. Under constant oxidative and mechanical stress, but devoid of organelles and deprived of biosynthetic capacity for protein renewal, RBCs undergo substantial homeostatic changes, progressive densification followed by late density reversal among others, changes assumed to have been harnessed by evolution to sustain the rheological competence of the RBCs for as long as possible. The unknown mechanisms by which this is achieved are the subject of this investigation. Each RBC traverses capillaries between 1000 and 2000 times per day, roughly one transit per minute, a total of about 2•105 transits during their lifespan. A dedicated Lifespan model of RBC homeostasis was developed as an extension of the RCM introduced in the first paper of this series to explore the cumulative patterns predicted for repetitive capillary transits over a standardized lifespan period of 120 days, using experimental data to constrain the parameter space. Capillary transits were simulated by periods of elevated cell/medium volume ratios and by transient deformation-induced permeability changes attributed to PIEZO1 channel mediation as outlined in the second paper of this series. The first unexpected finding was that quantal changes generated during single capillary transits cease accumulating after a few days and cannot account for the observed progressive densification of RBCs on their own, thus ruling out the quantal hypothesis. The second unexpected finding was that the documented patterns of RBC densification and late reversal could only be emulated by the implementation of a strict time-course of decay in the activities of the calcium and Na/K pumps, but only in addition to the quantal changes. These results showed that both quantal changes and pump-decay regimes were necessary to account for the documented lifespan pattern, neither sufficient on their own. They also suggested a strong selective component in the pump decay sequence. A third finding was that RBCs exposed to levels of calcium permeation above certain thresholds in the circulation could develop a pattern of late or early hyperdense collapse followed by delayed density reversal. When tested over much reduced lifespan periods the results emulated the known circulatory fate of irreversible sickle cells, the cell subpopulation responsible for vaso-occlusion and for most of the clinical manifestations of sickle cell disease. Analysis of the results provided an insightful new understanding of the mechanisms driving the changes in RBC homeostasis during circulatory aging in health and disease.

Function and hydrostatics in the telson of the Burgess Shale arthropod Burgessia

Burgessia bella is a characteristic Burgess Shale arthropod (508 Ma), but the unusual preservation of its telson in both straight and bent modes leads to contradictory interpretations of its function. A reinvestigation of the fossil material, including burial attitudes, combined with a comparison with the decay sequence and mechanics of the telson in living Limulus , demonstrates that the telson of Burgessia was flexible in its relaxed state but could be stiffened in life. Evidence of fluid within the telson indicates that this manoeuvrability was achieved by changes in hydrostatic pressure and muscular control. The dual mode in the Burgessia telson is, to my knowledge, the first documented among fossil arthropods. It indicates that the requirement for a rigid telson, which is resolved by a thick sclerotized cuticle in most arthropods, may first have been achieved by hydrostatic means.

The Half-Life of Titanium 44 and SN 1987A

The radioactive isotopes, such as 44Ti and 56Ni, are synthesized as a result of rapid nucleosynthesis in supernova explosions. The gamma-ray photons coming out from the decay sequence of 44Ti is now a strong candidate to explain the the late light curve of SN 1987A. It is noted here that the energy release from the 44Ti decay depends strongly on its half-life. However, the published values for 44Ti half-life display a large spread, ranging from ~ 35 to ~ 68 years. In this paper (Kumagai et al. 1997; see also Kumagai et al. 1993), we discuss the value of the half-life by comparing the theoretical light curves and the observations in SN 1987A. The unestablished half-life value is related to the ratio of the abundance of 44Ti to that of 56Ni.

Coarse woody debris in old-growth temperate beech (Nothofagus) forests of New Zealand

The volume, biomass, and carbon and nitrogen content of coarse woody debris were measured on three 1-ha reference plots in old-growth Nothofagusfusca (Hook. f.) Oerst.–Nothofagusmenziesii (Hook. f.) Oerst. forest on the South Island of New Zealand. Two decay sequences for logs and one for standing dead trees (snags) were recognised from two-way indicator species analysis (TWINSPAN) of up to 30 variables related to physical characteristics and structural integrity. Wood volume (up to 800 m3•ha−1) and biomass were high (up to 300 Mg•ha−1), and the inside-out decay sequence from heartwood to sapwood was unusual compared with that of other temperate hardwood forests. Coarse woody debris represented significant carbon and nitrogen pools, with ca. 150 Mg•ha−1 and 370 kg•ha−1, respectively, in one stand. The coarse woody debris component of these broad-leaved evergreen hardwood forests was much higher than that reported for other temperate hardwood forests and approaches that of many northern hemisphere conifer forests. The large coarse woody debris pools are discussed in relation to live stand biomass, natural disturbances and tree mortality, and decomposition processes.

DIRECTIONAL CORRELATIONS IN 127I

Gamma–gamma coincidence measurements on the decay of 9.3-hour 127Te to 127I form the basis of the decay scheme presented, which confirms the accepted decay sequence. Directional correlation measurements have been made on the 215–203 keV and 360–58 keV cascades. The respective correlation functions are:[Formula: see text]The directional correlation results have been interpreted in terms of the accepted spin sequence, and limits of multipole mixtures are presented. A short discussion of the collective properties of the levels is presented.

Pion and muon decay

The non-conservation of parity in pion and muon decay was discovered (Garwin, Lederman & Weinrich 1957; Friedman & Telegdi 1957) almost immediately after it had been observed in /?-decay. Experimentally it was shown that in the π - μ - e decay sequence the intensity of the final electrons had an angular distribution of the type I = A + B p μ ·p e´ where p μ (p e ) is the momentum of the muon (electron) at the point of emission. Since the muons were brought to rest between the two decay events, the connecting link could only be the muon spin. Equation (1) is thus the consequence of two separate equations, one for each decay process, pion decay σ μ = Cp μ, muon decay I = A + Dσ μ ·p e´