ELECTROCHEMICAL DETECTION OF HISTAMINE AND 5-HYDROXYTRYPTAMINE AT ISOLATED MAST-CELLS

The electrochemical oxidation of histamine has been investigated as an analytical tool. In a physiological buffer, histamine is oxidized at carbon fiber microelectrodes at potentials close to the background in a chemically irreversible process. Cylindrical carbon fiber electrodes were used as amperometric detectors for histamine separated with a re versed-phase capillary column, and detection limits of 240 amol were a chieved. Electrodes with beveled tips were used as real-time sensors b y monitoring with repetitive cyclic voltammograms at a scan rate of 80 0 V/s with a 16.7-ms repetition rate, and detection limits of 1.4 mu M were achieved. Both techniques were used to probe histamine and 5-hyd roxytryptamine (5-HT) stored in rat peritoneal mast cells. The content in single cells was measured by capillary HPLC, and both substances w ere found in single cells. Although the analysis revealed a large cell -to-cell variation in the amount of histamine and 5-HT, the average am ount was 150 and 4 fmol of histamine and 5-HT, respectively. Release o f histamine and 5-HT was measured with the electrode placed 1 mu m fro m the cell surface. Release was observed as a series of sharp concentr ation spikes, consistent with corelease of the two substances from ind ividual vesicles following exocytosis.