Changes of intracellular Ca++ as measured by arsenazo III in relation to the K permeability of human erythrocyte ghosts.

A Ca-sensitive dye, arsenazo III, has been incorporated into resealed human erythrocyte ghosts and calibrated to monitor continuously micromolar concentrations of intracellular ionized Ca ([Ca++]i). When the external concentration of Ca is much greater than [Ca++]i, [Ca++]i increases because of a net balance between Ca influx and efflux. Dynamic changes in [Ca++]i regulate K efflux, which in turn may influence the rate of Ca influx. A procedure for purifying arsenazo III is also described.