DIFFERENCES IN CA2-CELLS( PUMPING ACTIVITY BETWEEN SUBPOPULATIONS OF HUMAN RED)

It has been shown recently that the free Ca2+ content of human red cel ls rises during ageing in vivo. With the aim of determining the mechan isms involved in such a change, we have investigated some aspects of C a2+ homeostasis. Both the initial rate of Ca2+ influx and some kinetic parameters of the Ca2+ pump of human red cells were studied in light and dense sub-populations obtained through stringent, self-formed Perc oll gradients. At 37 degrees C and pH 7.4, no differences in Ca2+ entr y were found. By contrast, either at pH 7.0 or 7.4, the maximal Ca2+ e xtrusion rate of the approximately 10% heaviest cells was one-half of the corresponding lighter ones. The results demonstrate that the eleva ted free Ca2+ concentration distinctive of senescent cells, arises fro m a reduction in Ca2+ extrusion capacity during ageing. The possible p hysiological significance of this finding is discussed.