Effect of cell ageing on Ca2+ influx into human red cells

The effect of cell ageing on Ca2+ entry was studied in this work, using sub-populations of young and old human red cells, separated by stringent percoll density gradients. Additionally, the influence of an osmotic gradient was investigated as a model for shear stress. Ca2+ entry was assessed at 37 degrees C, under conditions where the Ca2+ pump was either inhibited by NaVO3 (0.5-10 mM) or inactivated by ATP depletion. The entry was linear with time up to 1 h. No differences in Ca2+ influx between the two sub-populations were detected in isotonic Na+-medium. In contrast, after incubation in anisosmotic media, Ca2+ entry into old cells was significantly higher than into younger cells. In hypotonic Na+-medium, the entry into old cells was not affected by La3+ (10 mu M) whilst it was partially blocked by Gd3+ at a similar level (half-maximal effect attained with about 1 mu M Gd3+). The entry into young cells was only slightly stimulated by these lanthanides at low concentrations (10 mu M), regardless of the tonicity of incubation medium. Further increasing Gd3+ levels above 10 mu M markedly enhanced Ca2+ entry into both cell types. The selective blockade of Ca2+ influx by low Gd3+ concentrations suggests presence of mechano-sensitive channels, that become preferentially activated in old cells. Activation of these channels during in-vivo microcirculation may help to explain the increased Ca2+ content of senescent cells. (C) Harcourt Publishers Ltd 1999.