Department of Physiology, University of Wisconsin Medical School, Madison 53706, USA.
Illumination with ultra-violet is used widely in physiological experiments for the photolysis of caged compounds. In the peptidergic cells of the pituitary gland, as well as cultured PC12 cells, ultra-violet light was found to produce changes in a number of membrane properties. Light of sufficient intensity to produce rapid photolysis of commonly used caged compounds induced changes in K+ and Ca2+ current, as well as changes in membrane capacitance. All responses to light showed a rapid timecourse, activating in a few ms and decaying within 10-50 ms after illumination ended. Experiments with radical scavengers and with inhibitors of cytochrome p450 and phospholipase A2 failed to block the light responses. These rapid responses to light emphasize that experiments employing ultra-violet light in the photorelease of physiological and pharmacological agents require special care for control of light artifacts.