Release of membrane-bound calcium by radiation and sulfhydryl reagents

Abstract Effects of ionizing radiation and of sulfhydryl reagents on the 45 Ca binding of red cell membranes were studied. Corresponding effects of these agents on potassium leak from intact red cells were also determined. Essentially all the 45 Ca associated with the ghosts appeared to be bound. Calcium binding could be described by assuming two independent groups of binding sites with dissociation constants of about 6 × 10 −4 m and 2 × 10 −4 m. The total binding capacity was about 2.5 × 10 −4 moles/g ghost protein. Membrane calcium was decreased by radiation and by the two sulfhydryl reagents, p‐chloromercuribenzoate (PCMB) and N‐ethyl maleimide (NEM). The tightly bound calcium fraction appeared to be most affected by these agents. Changes in potassium leak evoked by varying doses of agents appeared to parallel effects on membrane calcium. These investigations suggest that the increased cation permeability observed after exposure or red cells to radiation or sulfhydryl reagents may be related to alterations in the calcium‐binding properties of the cell membrane.