No abstract

Oxidant-induced damage has been proposed to be the underlying mechanism for loss of membrane phospholipid asymmetry in the erythrocyte membrane. In sickle cell disease, thalassemia, and diabetes as well as in senescent erythrocytes, an apparent correlation between oxidative damage and loss of phosphatidylserine asymmetry has been reported. In the present study, erythrocytes were subjected to various levels of oxidative stress and/or sulfhydryl modifying agents. The transmembrane location of phosphatidylserine (PS) was assessed by FITC-conjugated annexin V labeling and the PS-dependent prothrombinase assay. Transbilayer movement of spin-labeled PS was used to determine aminophospholipid translocase activity. Our data show that cells did not expose PS as the result of oxidative stress induced by phenylhydrazine, hydrogen peroxide, tert-butyl hydroperoxide, cumene hydroperoxide, or sulfhydryl modification by N-ethylmaleimide (NEM) and diamide, even under conditions that led to severe cellular damage and impairment of aminophospholipid translocase activity. In contrast, the increase of intracellular calcium induced by treatment with calcium and ionophore A23187 leads to a rapid scrambling of the lipid bilayer and the exposure of PS, which can be exacerbated by the inhibition of aminophospholipid translocase activity. Oxidation of the cells with hydrogen peroxide or phenylhydrazine did not affect A23187-induced uptake of calcium, but partly inhibited calcium-induced membrane scrambling. In conclusion, oxidative damage of erythrocytes does not induce exposure of phosphatidylserine on the membrane surface, but can interfere with both aminophospholipid translocase activity and calcium-induced randomization of membrane phospholipids.

In humans, XX maleness is the best known example of a sex reversal syndrome occurring with an incidence of one XX male among approximately 20,000 to 30,000 newborn boys. The karyotypes of the majority of these individuals are apparently normal, with respect to the numbers and structure of the chromosomes, but is in contradiction with the phenotypic sex which they display. XX maleness may be either a non Y-related mechanism triggered by a mutation on another chromosome or could be the result of the expression of some cytogenetically undetectable Y chromosome material present in the genome of such individuals. Recently, a number of human Y-specific single copy probes have been isolated. In this study, using several of these Y-specific probes we definitively demonstrate the presence of Y-chromosomal material in the genome of some 46,XX human males. These XX males carry only a fraction of the human Y chromosome. In the three positive cases reported here, presence of inclusive overlapping chromosomal fragments has been detected, implying a genetic heterogeneity of these patients.