Quantitative analysis of individual neurons by open tubular liquid chromatography with voltammetric detection

The ability to analyze individual cells is often important in biology because of the heterogeneity of tissue; this is especially true in the area of neurobiology. A method is described for the determination of trace levels of organic compounds in individual cells by open tubular liquid chromatography with voltammetric detection. In the method, a cell is isolated, an internal standard is added, the cell is homogenized and centrifuged, and the supernatant is injected directly onto the chromatography column. Since data are collected in both the electrochemical and chromatographic domains, the resolution of the method is better than that obtained by using amperometric detection. The combination of voltammetry and chromatography also aids in the identification of compounds. By use of this method three different neurons, D2, E4, and F1, from the land snail Helix aspersa are analyzed. The data show that the cells give certain unique and repeatable chemical profiles. Dopamine, serotonin, tyrosine, and tryptophan were identified and quantified in two of the cells at the femtomole level. In the third cell, only the two amino acids were observed and measured. The quantitative data indicate that the method is at least as reliable as other methods that have been applied to single cells and considerably more sensitive. The combination of qualitative and quantitative information allows for the chemical mapping of cells.