Subunit of the rod cyclic GMP-gated cation channel, which is involved in the final stage of the phototransduction pathway. When light hits rod photoreceptors, cGMP concentrations decrease causing rapid closure of CNGA1/CNGB1 channels and, therefore, hyperpolarization of the membrane potential. Forms a heterotetramer with CNGB1 in a 3:1 ratio. May also form cyclic nucleotide-activated homotetrameric channels, that are efficiently activated by saturating cGMP, but poorly activated by saturating cAMP compared to the heterotetramer with CNGB1. Rod cells in the retina. The C-terminal coiled-coil domain mediates homotrimerization of CNGA subunits. Belongs to the cyclic nucleotide-gated cation channel (TC 1.A.1.5) family. CNGA1 subfamily.