Calcium, potassium:sodium antiporter that transports 1 Ca(2+) and 1 K(+) in exchange for 4 Na(+). Critical component of the visual transduction cascade, controlling the calcium concentration of outer segments during light and darkness. Light causes a rapid lowering of cytosolic free calcium in the outer segment of both retinal rod and cone photoreceptors and the light-induced lowering of calcium is caused by extrusion via this protein which plays a key role in the process of light adaptation. Ca(2+)(out) + K(+)(out) + 4 Na(+)(in) = Ca(2+)(in) + K(+)(in) + 4 Na(+)(out) Highly expressed in the eye. The uncleaved signal sequence is required for efficient membrane targeting and proper membrane integration and topology. Belongs to the Ca(2+):cation antiporter (CaCA) (TC 2.A.19) family. SLC24A subfamily.