Photolysis of Caged Calcium Using a Low-Cost Flash Unit

Abstract

Photolabile calcium chelators have been designed to study intracellular calcium-dependent processes (1,2). These “caged” calcium compounds are useful tools to bypass rate limiting steps, i.e., in muscular excitation-contraction coupling (3–5). When using chelators intracellularly (6–8), it is possible to evoke a stepwise increase in the intracellular calcium concentration [Ca²⁺], by exposing the cells to high-intensity ultraviolet (UV) light. The minimum energy density required for photolysis of the caged calcium compound Nitr5 is approx 250 mJ/cm² in a wavelength band from 320 to 370 nm (9,10). The commonly used frequency-doubled ruby laser (6,7) meets these specifications during a flash of 25 ns, but is quite expensive. When a longer flash duration, ±4 ms, is acceptable, the commercially available xenon flashlamp developed by Rapp and Güth (11) can be used. At one-fourth of the price of the laser, it is still not a very economical alternative. We decided to develop a UV light source for the release of caged Ca²⁺ based on a standard photo flashlamp, costing one-tenth of the price of the commercially available xenon flash unit. An additional advantage of this system is that it is battery powered, thus avoiding interference on the power lines. A modified Metz® 60 CT 4 flash unit, which is widely used in professional photography, was used. When the unit is used for photographic applications, the UV light from the flashtube is absorbed by a filter in the front window, and a long flashtube is used to illuminate a large area evenly.