Fig. 6.

Endplate myopathy occurs in slow-channel transgenic mice with severe calcium overload. A, Neuromuscular junction from a 2-month-old αC418W mouse showing essentially normal ultrastructure of nerve terminus (white arrowheads), postsynaptic folds (black arrow), and junctional sarcoplasm (asterisk).B, Neuromuscular junction from 2-month-old αL251T mouse. The junctional sarcoplasm is filled with myriads of vacuole-like structures ranging in size from 0.05 to 1 μm (asterisk). Vacuoles are empty or filled with fluffy or granular material. Profiles of nuclei are present at either side of the accumulation of vacuoles. One nucleus appears severely degenerated (black arrow). In B and Cthe secondary synaptic folds and clefts are absent, and the nerve terminals (white arrowheads) are small and barely recognizable at the outer surface of the bulging postsynaptic regions.C, Neuromuscular junction from a εL269F mouse at 2 months. Vacuoles fill the junctional sarcoplasm and are present within the underlying sarcomeres (asterisk). The subsynaptic mitochondria are abnormally enlarged compared with those in the nerve terminus. Some show accumulations of dark, dense granules consistent with calcium (data not shown). Others contain multiple clear inclusions (black arrowhead). Some mitochondria are pathologically dilated (black arrow). One subsynaptic nucleus has normal ultrastructure. Scale bars: A, 0.9 μm;B, 4.1 μm; C, 1.5 μm.