A confocal laser scanning microscope designed for indicators with ultraviolet excitation wavelengths.

In this paper we describe the modifications necessary to upgrade, at affordable cost, a commercially available confocal laser scanning microscope for use with ultraviolet (UV) excitation. The optical problems associated with these modifications are described in detail, and easy solutions to solve them are suggested. The optical resolution of the instrument was tested with fluorescent beads and was found to be close to diffraction limited. The light losses due to lateral chromatic aberration were assessed in a thick fluorescent specimen and were found to be comparable to those usually observed with visible light. For a more visual example of the resolution of this instrument, isolated ventricular heart muscle cells were loaded with the fluorescent Ca2+ indicator indo 1. This allowed us to visualize subcellular structural detail and to illustrate the optical sectioning capability of the UV confocal microscope when recording indo 1 emission. Dual-emission line scans were used to perform ratiometric time-resolved detection of Ca2+ transients in voltage-clamped heart muscle cells loaded with the salt form of indo 1. The system presented in this paper should significantly broaden the range of fluorescent indicators that can be used in confocal microscopy.