About the Authors
Department of Biomedical Optics, Max-Planck Institute for Medical Research, Heidelberg, Germany
Department of Physiology and Biophysics, University of Washington, Seattle, Washington, United States of America
The authors have declared that no competing interests exist.
TE and WD designed the experiments with contributions by SEH and PBD. SEH performed most of the experiments, with TE contributing the remainder. The data were analyzed by SEH and TE and interpreted by SEH, TE, PBD, and WD. The paper was written by SEH, TE, PBD, and WD.