Lack of dystrophin but normal calcium homeostasis in smooth muscle from dystrophic mdx mice.

The free cytosolic Ca2+ concentration ([Ca2+]i) in the dystrophin-lacking smooth muscle from mdx mice was studied to gain new insights into the relation between dystrophin and cytoplasmic Ca2+ homeostasis, which was reported to be impaired in the mdx skeletal muscle. We observed that [Ca2+]i, as measured with the fluorescent Ca2+ indicator fura-2, was not elevated in resting smooth muscle of the vas deferens from mdx mice, in comparison with control C57 mice. Changes of the external Ca2+ concentration evoked similar changes of [Ca2+]i in mdx and control vas deferens. During contraction, cytosolic Ca2+ transients were identical, both in amplitude and in kinetics, whether or not dystrophin was present. Stretches evoked similar Ca2+ increases in muscles from both strains. Intracellular Ca2+ homeostasis appears to be unimpaired in mdx smooth muscle. Thus, the lack of dystrophin per se does not automatically induce a perturbation of Ca metabolism in muscle cells.