1. Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195-7290, USA
2. Department of Neurology, University of Washington, Seattle, WA 98195-7290, USA
3. Senator Paul D. Wellstone Muscular Dystrophy Cooperative Research Center, University of Washington, Seattle, WA 98195-7720, USA
4. Department of Biochemistry, University of Washington, Seattle, WA 98195-7290, USA