Mutations in the CNGA3 gene have been associated with complete and incomplete forms of autosomal recessive achromatopsia, a disorder that is characterized by reduced visual acuity, lack of color discrimination, photophobia and nystagmus. CNGA3 encodes the A-subunit of the cone cyclic nucleotide-gated (CNG) channel which is an essential component of the phototransduction cascade. The objective of this study was the electrophysiological analysis of mutant CNGA3 channels in a heterologous expression system. A3 channels with the point mutations R427C and R563C were analyzed as homooligomers and also as heterooligomers with the wildtype B-subunit present in native channels. In general, maximum currents were profoundly reduced in mutant channels, in homooligomers more so than in heterooligomers. Overall, the R563C mutant showed K_1/2 and h values for the activation by cGMP which are essentially the same as for wildtype channels while the cGMP-sensitivity of homooligomeric channels with the mutation R427C was increased by a factor of 10 and cAMP maximum currents were quadrupled. These effects were almost completely abrogated when coexpressing A3_R427C with B-subunits, which supports the hypothesis that the B-subunit in some cases partially compensates for the negative impact of an A3 mutation on the functionality of the channel (rescue effect).