Calcium homeostasis and cell death in Sol8 dystrophin-deficient cell line in culture

Abnormalities of calcium homeostasis are involved in the process of cell in juries such as Duchenne muscular dystrophy characterized by the absence of the protein dystrophin. But how the absence of dystrophin leads to cytosoli c calcium overload is as yet poorly understood. This question has been addr essed with skeletal muscle cells from human DMD muscles or mdx mice. Althou gh easier to obtain than human muscles, mdx muscle cells have provided cont roversial data concerning the resting intracellular calcium level ([Ca2+](i )). This work describes the culture of So18 cell line that expresses neithe r dystrophin nor adhalin, a dystrophin-associated protein. The [Ca2+](i) an d intracellular calcium transients induced by different stimuli (acetylchol ine, caffeine and high potassium) are normal during the first days of cultu re. At later stages, calcium homeostasis exhibits drastic alterations with a breaking down of the calcium responses and a large [Ca2+](i) elevation. C oncomitantly, So18 cells exhibit morphological signs of cell death like cyt oplasmic shrinkage and incorporation of propidium iodide. Cell death could be significantly reduced by blocking the activity of calpains, a type of ca lcium-regulated proteases. These results suggest that So18 cell line provid es an alternative model of dystrophin-deficient skeletal muscle cells for w hich a clear disturbance of the calcium homeostasis is observed in culture in association with calpain-dependent cell death. It is shown that transfec tion with a plasmid cDNA permits the forced expression of dystrophin in So1 8 myotubes as well as a correct sorting of the protein. This approach could be used to explore possible interactions between dystrophin deficiency, ca lcium homeostasis alteration, and dystrophic cell death. (C) 2001 Harcourt Publishers Ltd.