The osmotic response of human erythrocytes and the membrane cytoskeleton

Abstract

The volumes of human erythrocytes suspended in solutions of varying concentrations of sodium chloride and sucrose were measured by a Coulter Channelyzer Model H4 with appropriate corrections. The cells showed greatly restricted volume changes at osmolarities between 200-700 mOsm. At osmolarities outside this limit, on the other hand, the cells showed nonrestricted volume changes following essentially the predictions of an ideal osmometer. This unexpected volume response was not spuriously due to changes in shape or to a changing orientation of the cells as they traversed the aperture. The restricted volume change observed was abolished when the cells had previously been treated with diamide or had been heated for 60 minutes at 50 degrees C, conditions that are known to disturb the spectrin-actin network. The possibility must be considered that the osmotic behavior of human erythrocytes may be nonideal and that this nonideal behavior is primarily due to mechanical restriction provided by the spectrin-actin network of the membrane cytoskeleton.

Alternative interpretation for the osmotic response of human erythrocytes

“…The solid points and associated straight line represent the "true" volumes, after having quantitatively corrected the "measured' volumes for shape factor, according to the method of Richieri et al (1985a,b). Since the deviation between the straight line and the raw-data curve in Figure 2 is clearly within the same range as that shown in Figure 1 (and also estimated from other similar plots of Heubusch et al, 1985), it can be stated that the shape factor correction alone can similarly account for the deviations in the hypotonic range of their data.We have found that the same linearization effect also results from the similar correction of other of our osmotic pressure-volume data, taken under different conditions (of temperature, PBS composition, pH, etc.) but at the same slow-flow rate through the orifice.…”

“…In contrast, increased chemical nonideality and eventual hemolysis are the likely factors responsible for the behavior in t h e hypertonic range. Figure 1 reproduces a plot of osmotic volume changes reported by Heubusch et al (1985) for erythrocytes in dilute saline (NaC1) solutions (from Heubusch et al, 1985; Fig. 1).…”

“…At this flow rate, the data are well fit using the oblate assumption for the erythrocyte shape witin the orifice (Richieri et al, 1985a). If the data of Heubusch et al (1985) were taken at the more typical Coulter flow rate of 4 d s e c , the contribution of the shape factor correction, now more closely based on the prolate assumption, should be even larger.It is not clear why Heubusch et al (1985) were unable to apply the shape factor correction successfully, since their procedure was apparently the same as that used …”

“…It is not clear why Heubusch et al (1985) were unable to apply the shape factor correction successfully, since their procedure was apparently the same as that used…”

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“…In addition, membrane-skeleton and cell-skeleton proteins can restrain cell swelling [19] and thus interfere with osmotically driven cell fusion. Proteinases are important in chemically induced cell fusion , and the fusion of erythrocytes by some chemical fusogens involves the proteolysis of ankyrin by a serine proteinase [23] and the proteolysis of band 3 by a calcium-activated proteinase [23,24].…”