Erythrocytes lack mitochondria and nuclei and consist mainly of hemoglobin, a complex molecule containing heme groups whose iron atoms temporarily link to oxygen molecules in the lungs or gills and release them throughout the body.
The membrane contains different ion channels like the Ca²⁺-activated K⁺ channels, or the volume-sensitive Na⁺/K⁺ pump. Studies also revealed the participation of ion channels in the regulation of erythrocyte 'apoptosis'. Osmotic shock, oxidative stress and energy depletion all activate a Ca²⁺-permeable non-selective cation channel in the erythrocyte cell membrane.