48 Biochirnica et Biophysica Acta 857 (1986) 48-60 Elsevier BBA 73045 Anomalous permeability and stability characteristics of erythrocytes in non-electrolyte media D. Sambasivarao, N.M. Rao, and V. Sitaramam National Institute o/Nutrition, Indian Council of Medical Research, Jamai Osmania PO, Hyderabad 500007, A.P. (India) (Received October 8th, 1985) Key words: Hypertonic disruption; Osmolysis; Membrane surface charge; Ionic detergent; (Rat erythrocyte) The permeability characteristics of the erythrocyte membrane were critically evaluated in electrolyte and non-electrolyte (sucrose) media by ion-selective electrodes and radioactive polyol fluxes as well as by the novel technique of osmometry. K + e/flux demonstrated a linear osmotic susceptibility distinct from Na + influx upon incubation in NaCl media of various tonicities. In non-electrolyte media, acidification of the medium, large fluxes of K +, sucrose and even haemoglobin (as manifest by hypertonic disruption) were consistent with enhanced porosity of the bilayer due to the field created by surface charge density leading to density fluctuations in the bilayer. Introduction Despite major efforts over half a century, several ambiguities persist in the understanding of the behaviour and stability of erythrocytes in electro- lyte and non-electrolyte media [1-6]. The stabil- ity/lysis of erythrocytes can be categorized broadly into osmotic and non-osmotic mecha- nisms. The osmotic mechanism of lysis, which includes hypotonic and colloidal lysis, is primarily mechanical and is characterized by influx of water due either to low osmolality of the external medium or to a decrease in the reflection coeffi- cients to the external osmolytes due to a change in membrane porosity. Non-osmotic mechanisms in- clude physical disruption due to detergency, toxins, action of lipases, etc., and involve a perturbation in the bilayer structure rather than mere influx of water. A testable consequence of such a distinction lies in the retarding influence of hypertonicity only on the osmotic mechanism of lysis. The ab- sence of such a clear distinction, compounded by lack of adequate osmotic methodology, has re- sulted in much ambiguity in the past. For in- stance, suspension of erythrocytes from a variety of species in non-electrolyte media was known to result not only in ion and solute fluxes but also in lysis [1-3,5-8]. Changes in the volume (cf. Ref. 9) of a perfect osmometer cannot exist without con- comitant osmolyte fluxes (cf. Refs. 2 and 3). Simi- larly osmolyte fluxes are inconsistent with the notion of invariant isotonicity. Neglect of these logical contradictions has led to considerable con- fusion with regard to the mechanism of lysis in hypertonic electrolyte and non-electrolyte media, on resuspension of the cells into so-called isotonic media (cf. Refs. 2 and 3). An explanation for electrolyte fluxes, on suspension of erythrocytes in non-electrolyte media, was thus far restricted to reversal of Donnan potentials across a membrane of invariant semipermeability (cf. Ref. 1), which would be untenable if the bulk porosity of the membrane changed even to non-electrolytes such as polyols. Since the primary mechanistic distinction lies in the influence of external osmotic pressure on lysis, we investigated, in depth, the influence of 0005-2736/86/$03.50 © 1986 Elsevier Science Publishers B.V. (Biomedical Division)