1. Department of Chemistry, Marquette University, P.O. Box 1881, Milwaukee, Wisconsin 53201-1881, United States
2. Department of Physiology & Membrane Biology, University of California, 1 Shields Avenue, Davis, California 95616, United States
3. Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York 10065, United States
4. Department of Chemistry, University of Texas at Austin, 1 University Station, Austin, Texas 78712, United States
5. Department of Neuroscience, University of Texas at Austin, 1 University Station, Austin, Texas 78712, United States