Ethical and psychosocial issues related to interferon alpha therapy for chronic hepatitis C

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The initial rate of net Mg2+ efflux was measured in human red blood cells by atomic absorption. In fresh erythrocytes incubated in Na+,K+-Ringer's medium this rate was 7.3 ± 2.8 μmol/I cells per h (mean±S.D. of 14 subjects) with an energy of activation of 13 200 cal/mol. Cells with total Mg2+ contents ([Mg]i) ranging from 1.8 to 24 mmol/l cells were prepared by using a modified p-chloromercuribenzenesulphonate method. Mg2+ efflux was strongly stimulated by increases in [Mg]i and in external Na+concentrations ([Na]o). A kinetic analysis of Mg2+ efflux as a function of [Mg]i and [Na]o revealed the existence of two components: (i) an Na+-stimulated Mg2+ efflux, which exhibited a Michaelian-like dependence on free internal Mg2+ content (apparent dissociation constant = 2.6 ± 1.4 mmol/l cells; mean ± S.D. of six subjects) and on external Na+ concentration (apparent dissociation constant = 20.5 ± 1.9 mM; mean ± S.D. of four subjects) and a variable maximal rate ranging from 35 to 370 μmol/l cells per h, and (ii) an Na+-independent Mg2+ efflux, which showed a linear dependence on internai Mg2+ content with a rate constant of (6.6 ± 0.7) · 10−3 h−. Fluxes catalyzed by the Na+-stimulated Mg2+ carrier were partially dependent on the ATP content of the cells and completely inhibited by quinidine (IC50 = 50 μM) and by Mn2+ (IC50 = 0.5–1.0 mM).