COS 7 or HEK293 cells transfected with the cDNA for rabbit RYR1 carrying point mutations introduced by site directed mutagenesis 19, 62, 63, myotubes generated from muscle biopsy tissue 44, 64 66 and 1B5 dyspedic myotubes transduced with wild type and mutated RYR1 cDNA 67 accutane symptoms