1. O. Orwar, A. Moscho, H. A. Fishman, R. N. Zare, Department of Chemistry, Stanford University, Stanford, CA 94305, USA.
2. K. Jardemark and I. Jacobson, Department of Anatomy and Cell Biology, Göteborg University, S-413 90, Göteborg, Sweden.
3. R. H. Scheller, Department of Molecular and Cellular Physiology, Howard Hughes Institute, Stanford University, Stanford, CA 94305, USA.