1. *Interuniversitary Institute of Myology, Department of Basic and Applied Medical Sciences, CeSI-, Università degli Studi G. d'Annunzio, I-66013 Chieti, Italy;
2. Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, NY 14642; and
3. Telethon Electron Microscopy Core Facility, Department of Cell Biology and Oncology, Consorzio Mario Negri Sud, I-66030 Santa Maria Imbaro, Chieti, Italy