1. Institute for Biology, Experimental Biophysics, Humboldt Universität zu Berlin, D-10115 Berlin, Germany.
2. Institute for Synaptic Physiology, Center for Molecular Neurobiology Hamburg, Falkenried 94, D-20251 Hamburg, Germany.
3. Institute of Physical Chemistry, Karlsruhe Institute of Technology, Karlstrasse 12, D-76131 Karlsruhe, Germany.