Development of cell hypoxia induced by factors of long-term spaceflight

Abstract

308 Changes in erythrocyte shape and plasma membrane viscosity and selective permeability were studied as well as the content of oxygen and the efficiency of its retention by human erythrocytic hemoglobin after a long-term spaceflight (LSF) were determined. It has been found that 24 h after LSF, the discocyte count decreases, the plasma membrane viscosity and the activities of Na + /H + exchange and Ca 2+ -dependent a + channel increase, Ca 2+ -ATPase activity and the hemoglobin content decrease, and the efficiency of O 2 retention by hemoglobin increases. It is assumed that the detected changes are the cellular factors that are involved in hypoxia development in humans during LSF. LSF factors (zero gravity, the action of electromagnetic fields and radiation, hypodynamia, and psychological stress) cause integrated changes in the red blood lineage of cosmonauts [1‐6]. Decrease in the erythrocyte count and hemoglobin content accompanied by an increase in the count of transformed erythrocytes, changes in the plasma membrane permeability and cell metabolism, increase in the relative cholesterol concentration, and decrease in the level of phospholipids in the plasma membrane have been recorded [2, 7]. A decrease in the ATP content both during and after LSF is associated with the activation of active ion transport, possible changes in the state of plasma membrane, and altered hemoglobin synthesis. It is important that the LSF factors cause changes in both the hemoglobin composition (increase in the fraction of A 2 hemoglobin and methemoglobin and decrease in the activity of methemoglobin reductase) and physicochemical properties of globin (shift in hemoglobin isoelectric point to the alkaline region) [6]. Characteristic changes in the erythrocyte shape caused by the LSF factors have been detected. More precisely, the specific morphological features of the erythrocyte include changes in the diameter, hemoglobin content and concentration, and cell thickness and volume. Erythrocyte has the shape of a biconcave disc, which is optimal for the oxygen diffusion into the cell. In the case of spherical erythrocytes, the central part of the cell is less saturated with oxygen than the surface layers. In addition, erythrocyte in this case loses the ability to rapidly and reversibly change its configuration to pass freely through the spleen capillaries and sinuses. This may considerably influence its lifespan [6, 7]. The decreased count of discocytes and increased counts of transformed erythrocyte forms (spherocytes, stomatocytes, knizocytes, and echinocytes) is observed during the first days after LSF [2]. It has been found that the average erythrocyte volume, thickness, and specificity increase after LSF, whereas the average surface area decreases. LSF influences not only the cell shape, but also the electrophoretic mobility of hemoglobin molecule, which is likely to be accompanied by changes in the protein redistribution in the cytoplasm. We have earlier demonstrated that characteristic changes in the erythrocyte shape and volume as well as the cell plasma membrane viscosity and permeability