Single cell endocrinology: analysis of P-450scc activity by fluorescence detection methods.

A mechanism-based, fluorogenic probe for the cytochrome P-450scc (cholesterol side chain cleavage) enzyme, rate-limiting for the conversion of cholesterol to steroid hormones, is introduced and its application to the study of enzyme activity and regulation in single steroidogenic cells by several fluorescence detection methods is demonstrated. Reaction of the probe with P-450scc gives pregnenolone and the highly fluorescent resorufin anion. Spectroscopic changes in probe fluorescence, indicative of P-450scc activity, were monitored by steady-state fluorescence spectroscopy, flow cytometry, and microspectrofluorometry. This unique probe provides a nonradiometric indicator for real-time measurement of P-450scc activity in single living cells.

Immunofluorescent flow cytometry in N dimensions. The multiplex labeling approach.

The problem of the simultaneous use in flow cytometry of N greater than 2 antibodies in conjunction with two fluorochromes was investigated. Theoretical analysis led to a labeling procedure and reconstruction formula that allow N-dimensional labeling distributions to be obtained from two-dimensional fluorescence distributions. The general problem of M greater than or equal to 2 fluorochromes and N greater than M antibodies was shown to be reducible to the case of two fluorochromes. The method was tested by a triple labeling analysis of murine thymocytes.

An automated device for the preparation of complex reagent mixtures. The immunofluorescence tomograph.

A microcomputer-controlled device was built that automatically prepares small volumes of mixtures of up to eight reagents. The operation of the system is fast, flexible, and reliable, thus making possible the routine use of experimental protocols that require large numbers of small volume reagent samples, each having a different composition. In particular, the software we developed for this device handles the preparation of three-antibody staining solutions to be used in triple labeling immunofluorescent flow cytometry experiments that involve only two fluorochromes. In this role, the device is known as an "Immunofluorescence Tomograph."

Automated single-cell manipulation and sorting by light trapping.

Following the recently reported trapping of biological particles by finely focused laser beams, we report on the automated micromanipulation of cells and other microscopic particles by purely optical means as well as on a newly observed interaction between particles in the trapping beam. A simple instrument is described which allows single cells to be positioned with high accuracy, transported over several millimeters, and automatically sorted on the basis of their optical properties. These operations are performed inside a small enclosed chamber without mechanical contact or significant fluid flow. Potential applications of this technique in experimental cell biology are discussed.