1. Institute for Biology, Experimental Biophysics, Humboldt-Universität zu Berlin, D-10115 Berlin, Germany.
2. Institute for Synaptic Physiology, Center for Molecular Neurobiology Hamburg, University Medical Center Hamburg-Eppendorf, D-20251 Hamburg, Germany.
3. Department of Molecular Sensory Systems, Center of Advanced European Studies and Research (caesar), Ludwig-Erhard-Allee 2, 53175 Bonn, Germany.