Visual signal transduction is mediated by a G-protein coupled cascade using cGMP as second messenger. This protein can be activated by cGMP which leads to an opening of the cation channel and thereby causing a depolarization of rod photoreceptors. Induced a flickering channel gating, weakened the outward rectification in the presence of extracellular calcium, increased sensitivity for L-cis diltiazem and enhanced the cAMP efficacy of the channel when coexpressed with CNGA3. Essential for the generation of light-evoked electrical responses in the red-, green- and blue sensitive cones (By similarity). Tetramer formed of three CNGA3 and one CNGB3 modulatory subunits. Defects in CNGB3 are a cause of cone degeneration (cd). Cd is characterized by day-blindness and absence of retinal cone function. This autosomal recessive disorder occurs naturally in the Alaskan Malamute and German Shorthaired Pointer breeds. Belongs to the cyclic nucleotide-gated cation channel (TC 1.A.1.5) family. CNGB3 subfamily.