A c.896G>A mutation was engineered in exon 7 changing arginine codon 299 to a glutamine codon (p.Arg299Gln). This mutation is the equivalent of the human R302Q mutation which causes increased unstimulated activity and is associated with a cardiac phenotype. An FRT site flanked neomycin resistance gene cassette was inserted into intron 6 and removed later through flp-mediated recombination. In addition, loxP sites were inserted within intron 6 upstream and within intron 7 downstream from the mutation. (J:235379, J:256296)