Cation-sensitive pore formation in rehydrated erythrocytes.

Rehydration of red blood cells (RBC) in isotonic media after dehydration in hypertonic electrolyte or nonelectrolyte saline leads to their posthypertonic hemolysis (PH). Ca2+ ions at a concentration of more than 5 mM stimulated hemolysis of RBC treated by hypertonic sucrose but not NaCl if rehydration was carried out in the presence of cations. Zn2+ produced a more complex response of stimulation followed by inhibition as a concentration is increased. Mg2+, Ca2+, Zn2+, EDTA and sucrose exhibited only inhibition when added to isotonic NaCl media immediately after onset of rehydration or later on. At low ionic strength inhibition produced by divalent cations was markedly reduced and sucrose was ineffective. An equimolar concentration of EDTA abolished the inhibition of PH by Zn2+ ions if they were introduced into the isotonic media after the cells, but activated hemolysis when rehydration was carried out in the presence of ions. The same divalent cations prevented shape transformation and hemolysis induced by melittin if they interacted with the plasma membrane prior to the addition of melittin. Subsequent chelation of cations by EDTA triggers the full sequence of events characteristic to the action of melittin alone and resulted in cell spherulation followed by hemolysis. Inhibition of melittin-induced hemolysis produced by all cations was reversible because EDTA abolished the action of divalent cations and even stimulated hemolysis in isotonic sucrose. Similarities in the mode of action of divalent cations and EDTA on posthypertonic hemolysis which is attributed to endogenous stimuli and melittin-induced hemolysis as far as the exogenous agent is concerned imply that in both cases common intrinsic mechanisms are involved in the process of cation-sensitive pore formation in erythrocyte membranes, while differences indicate that more complex pores are formed during posthypertonic injury.