Spots were picked in MilliQ water and prepared for and analyzed by MALDI-TOF/TOF mass spectrometry as described before. Data interpretation was carried out using the GPS Explorer software (V3.5) and database searching using the Mascot program (V2.2) (www.matrixscience.com). Since all experiments were performed on rat INS-1E cells, MS/MS searches were conducted with the following settings: UniProt_sprot (517100 sequences; 182146551 residues, release date June 2010) with the taxonomy set on Rodentia (25375 sequences) and UniProt_trembl (10867798 sequences; 3502326038 residues, release date June 2010) with the taxonomy set on Rodentia (87619 sequences). MS/MS tolerance for precursor ions was set on 0,2 Da and fragment ions on 0,4 Da, methionine oxidation as variable modification and carbamidomethylation of cysteine as fixed modification. As enzyme, trypsin was selected and a maximum of one missed cleavage was allowed. Using these parameters the probability-based MOWSE scores greater than the given cut-off value for MS/MS fragmentation data were taken as significant (p<0.05). For protein identifications where no hit was found in the rat databases, protein identity was based on comparison with the orthologous mouse sequence (Supplemental table 1). The biological processes, localization and functions of the proteins were extracted from Gene Ontology (GO) using the automated STRAP tool. The function and pathway enrichment of the identified proteins was assessed using Ingenuity Pathway Analysis software (IPA version 8.6; build 93815; content version 3003, 2010-04-29).