title: Effects of age-dependent membrane transport changes on the homeostasis of senescent human red blood cells.
abstract: Little is known about age-related changes in red blood cell (RBC) membrane transport and homeostasis. We investigated first whether the known large variation in plasma membrane Ca(2+) (PMCA) pump activity was correlated with RBC age. Glycated hemoglobin, Hb A1c, was used as a reliable age marker for normal RBCs. We found an inverse correlation between PMCA strength and Hb A1c content, indicating that PMCA activity declines monotonically with RBC age. The previously described subpopulation of high-Na(+), low-density RBCs had the highest Hb A1c levels, suggesting it represents a late homeostatic condition of senescent RBCs. Thus, the normal densification process of RBCs with age must undergo late reversal, requiring a membrane permeability increase with net NaCl gain exceeding KCl loss. Activation of a nonselective cation channel, Pcat, was considered the key link in this density reversal. Investigation of Pcat properties showed that its most powerful activator was increased intracellular Ca(2+). Pcat was comparably selective to Na(+), K(+), choline, and N-methyl-D-glucamine, indicating a fairly large, poorly selective cation permeability pathway. Based on these observations, a working hypothesis is proposed to explain the mechanism of progressive RBC densification with age and of the late reversal to a low-density condition with altered ionic gradients.
authors: Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, United Kingdom. vll1@cam.ac.uk
authors: Virgilio L
authors: VL
authors: Lew
authors: Nuala
authors: N
authors: Daw
authors: Zipora
authors: Z
authors: Etzion
authors: Teresa
authors: T
authors: Tiffert
authors: Adaeze
authors: A
authors: Muoma
authors: Laura
authors: L
authors: Vanagas
authors: Robert M
authors: RM
authors: Bookchin
mesh_terms: D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D002463:Cell Membrane Permeability; D004905:Erythrocyte Aging; D004910:Erythrocyte Membrane / Q000378:metabolism; D004912:Erythrocytes / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D006442:Glycated Hemoglobin / Q000378:metabolism; D006706:Homeostasis; D006801:Humans; D053499:Plasma Membrane Calcium-Transporting ATPases / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism
chemical_list: D006442:Glycated Hemoglobin; D053499:Plasma Membrane Calcium-Transporting ATPases; D011188:Potassium; D012964:Sodium; C517652:hemoglobin A1c protein, human