Amperometry and cyclic voltammetry of tyrosine and tryptophan‐containing oligopeptides at carbon fiber microelectrodes applied to single cell analysis

Abstract

AbstractThe amperometric and cyclic voltammetric detection of α‐melanocyte stimulating hormone (MSH), β‐endorphin, and corticotropin‐like intermediate lobe peptide (CLIP), all proopiocortin (POC) derived peptides secreted from melanocytes of the pituitary intermediate lobe, at carbon fiber microelectrodes was investigated. For amperometry, it was found that all of these peptides could be detected; however, fouling of the electrodes reduced the response of the electrode after successive application of the peptide in flow injection experiments. The fouling was apparently due to oxidation of tyrosine in the peptides as similar results were found for tyrosine but not tryptophan. The effect of fouling could be reversed if the electrode was electrochemically treated by scanning from −1.0 V to +1.0 V at 300 V/s for 2 min between application of the peptides. Using cyclic voltammtery at 800 V/s, it was possible to distinguish MSH, which had a peak shaped voltammogram, from the other POC peptides, which had relatively flat voltammetric waves at this scan rate. The scan rate dependence of the peak current for MSH revealed that the voltammetry was adsorption controlled. As a result, in a monitoring application, where voltammograms are continuously obtained with a fixed interval between them, decreasing the interval increases the temporal resolution but decreases the sensitivity for MSH. It was found that when monitoring the current in the potential range of 0.90 to 1.00 V, the temporal response to MSH was dependent upon the potential window used for scanning. Using high scan rates and a potential window 0 to 1.2 V, it was possible to monitor exocytosis from single melanocytes and use the voltammogram to demonstrate detection of MSH from the cells.