Maturation of macroreticulocyte membranes in vivo.

Abstract

Abstract Maturaton of macroreticulocyte membranes was studied over 11 days in 2 animal models in vivo. (1) Reticulocytosis was induced by acute blood loss in rats and halted by irradiation; and (2) reticulocytosis was established in polycythemic rats by exchange transfusion. Reticulocytes fell from 46.1 per cent (in irradiated rats) and 30.7 per cent (in exchanged rats) to normal by day 5. Mean cell volume of reticulocytes decreased 29 per cent (from 108 μ 3 to 77 μ 3 ; normal=63 μ 3 ), and mean cell hemoglobin content decreased 26 per cent (from 29.7 to 21.9 μμg; normal=20.8 μμg). The measured 51 Cr half-survival of reticulocyte-rich blood was decreased 1.5 to 1.9 days, but cell survival was normal when corrected for the loss of hemoglobin (and 51 Cr) per cell during maturation. Young reticulocytes (mean age in the circulation=0.25 days) had a cholesterol content 2.5-fold and phospholipid content 4-fold that of mature red cells. They lost 44 per cent of this cholesterol and 67 per cent of this phospholipid during maturation. Isolated plasma membranes of reticulocytes had a cholesterol:phospholipid molar ratio (C:P) equal to that of mature cells. These membranes accounted for 50 per cent of the phosphoiipid and greater than 80 per cent of the cholesterol of young reticulocytes. Approximately 13 of this lipid was lost during maturation. The mitochondrial fraction was cholesterol-poor. It appeared to be lost largely during the first 2 days of reticulocyte maturation and completely by day 5. Splenectomy decreased the rate and extent of lipid loss during reticulocyte maturation resulting in mature red cells rich in lipid. Nonetheless, the loss of plasma membrane lipid in splenectomized animals was 75 per cent of that occuring in animals with intact spleens. These studies demonstrate that the macroreticulocyte loses substantial amounts of lipid during maturation. Much of this results from the loss of phospholipid-rich intracellular organelles, primarily, mitochondria. However, macroreticulocytes also lose approximately 13 of their plasma membrane lipids during maturation due to factors operative in vivo. The spleen is one of these factors.