Portable fluorescence photometer for monitoring free calcium

We introduce a compact and portable photometric system for measurements of the calcium dynamics in cells. The photometer is designed for applications in centrifuges or in zero gravity environment and thus extremely compact an d reliable. It operates with the calcium-sensitive dye Indo-1. The excitati on wavelength of 345 nm is generated by frequency doubling of a laser diode . Two compact photomultiplier tubes detect the fluorescent emission. The el ectronics provide the sensitivity of photon counting combined with simultan eous measurement of the temperature, of air pressure, and of gravitational force. Internal data storage during the experiment is possible. A newly dev eloped cell chamber stabilizes the cell temperature to 37.0 +/-0.1 degreesC and includes a perfusion system to supply the cells with medium. The syste m has a modular setup providing the possibility of changing the light sourc e and detectors for investigation of ions other than calcium. Measurements of the intracellular calcium concentration are based on a comprehensive cal ibration of our system. First experiments show that the calcium dynamics of osteosarcoma cells stimulated by parathyroid hormone is observable. (C) 20 00 American Institute of Physics. [S0034-6748(01)00301-X].