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 and inner medulla of kidney. 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.