Differences in Ca2+ pumping activity between sub-populations of human red cells.
It has been shown recently that the free Ca2+ content of human red cells rises during ageing in vivo. With the aim of determining the mechanisms involved in such a change, we have investigated some aspects of Ca2+ 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 Percoll gradients. At 37 degrees C and pH 7.4, no differences in Ca2+ entry were found. By contrast, either at pH 7.0 or 7.4, the maximal Ca2+ extrusion rate of the approximately 10% heaviest cells was one-half of the corresponding lighter ones. The results demonstrate that the elevated free Ca2+ concentration distinctive of senescent cells, arises from a reduction in Ca2+ extrusion capacity during ageing. The possible physiological significance of this finding is discussed.
Romero
P J
PJ
Instituto de Biología Experimental, Facultad de Ciencias, Universidad Central de Venezuela, Caracas, Venezuela.
Romero
E A
EA
D002118:Calcium / Q000097:blood*; D000252:Calcium-Transporting ATPases / Q000097:blood*; D004905:Erythrocyte Aging; D004912:Erythrocytes / Q000166:cytology* / Q000378:metabolism; D006706:Homeostasis; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009994:Osmolar Concentration
D000252:Calcium-Transporting ATPases; D002118:Calcium