Ca2+ transport activities of inside-out vesicles prepared from density-separated erythrocytes from rat and human.
The plasma membrane Ca2+ ATPase in erythrocytes is vital for the maintenance of intracellular Ca2+ levels. Since the cytoplasmic Ca2+ concentration is elevated in older erythrocytes, the properties of the Ca2+ transport ATPase were examined during cell aging using inside-out vesicles (IOVs) prepared from density-separated, young (less dense, Ey) and old (more dense, Eo) rat and human erythrocytes. The transport of Ca2+ and the coupled hydrolysis of ATP were measured using radiolabeled substrates. The calmodulin-independent Ca2+ transport activity (Ey, 38.8 vs. Eo, 23.3 nmols/min/mg IOV protein) and the Ca2+ dependent ATP phosphohydrolase activity (Ey, 53.5 vs. Eo, 48.8 nmols/min/mg protein) were greater in IOVs prepared from younger (less dense) rat erythrocytes. The calmodulin-independent Ca2+ transport activity in IOVs from human erythrocytes was 12.9 nmols/min/mg IOV protein for Ey and 10.7 nmols/min/mg IOV protein for Eo. Inside-out vesicles from older (more dense) cells exhibited a lower pumping efficiency as determined by the calculated stoichiometry, molecule of Ca2+ transported per molecule of ATP hydrolyzed (rat: Ey, 0.74 vs. Eo, 0.49; human: Ey, 1.22 vs. Eo, 0.77). The enzymatic activity of rat and human Ey IOVs was labile. The Ca2+ transport activity in Ey but not Eo IOVs rapidly declined during cold storage (4 degrees C). The decrease in Ca2+ transport activity during aging may accentuate the age-related decline in several erythrocytic properties.
Seidler
N W
NW
Department of Biochemistry & Molecular Biology, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark.
Swislocki
N I
NI
D000110:Acetylcholinesterase / Q000097:blood; D000255:Adenosine Triphosphate / Q000097:blood; D000818:Animals; D002118:Calcium / Q000097:blood*; D000252:Calcium-Transporting ATPases / Q000097:blood*; D002458:Cell Fractionation; D004905:Erythrocyte Aging; D004910:Erythrocyte Membrane / Q000378:metabolism*; D004912:Erythrocytes / Q000378:metabolism; D006801:Humans; D051381:Rats
D000255:Adenosine Triphosphate; D000110:Acetylcholinesterase; D000252:Calcium-Transporting ATPases; D002118:Calcium