A cassette containing the non-coding exon 1, and a neo/PGK cassette flanked by loxP sites followed by exon 2 that contains the whole Gja1 coding sequence including the mutations S255A, S262A, S279A, and S282A, was inserted into the endogenous locus. The neomycin selection cassette was removed by breeding with Tg(CMV-cre)1Cgn mice. These serine to alanine mutations prevent Gja1 phosphorylation by mitogen-activated protein kinase.