Total ion content of skeletal and cardiac muscle in the mdx mouse dystrophy: Ca2+ is elevated at all ages.

The mdx mouse has been shown to have a gene defect at the locus which is homologous to that which is defective in Duchenne muscular dystrophy and they both lack dystrophin, the protein product of this defective gene. The exact cause of myofibre necrosis in DMD is not known but there is evidence to support a causal relationship between elevated calcium and tissue necrosis. Since the mdx mouse exhibits age-dependent changes in the proportion of tissue necrosis, we have measured total ion content (Ca2+, Na+, K+, and Mg2+) in the heart and skeletal muscle of animals at different ages to determine if ionic changes correlate with reported periods of necrosis. Total calcium is elevated throughout the ages studied (10 days, 30 days and 254-347 days) in both tissues and does not correlate with necrosis, although it appears that pre-necrotic tissues do not exhibit such a wide variation in calcium content as is observed in tissues from older animals. These changes are discussed with reference to the other ions measured and to the regulation of intracellular calcium.