Controlling calcium release in spatially distinct regions. A, B and C, schematic illustration of the position of the area (pink circle) inside the nucleus or the cytoplasm that was illuminated with UV light for photolysis of NP-EGTA; arrows indicate the directions of calcium signal spreading analyzed. D, schematic illustration of image acquisition and calcium release that were performed simultaneously using a confocal laser-scanning microscope. The path of the laser beam (blue line) controlled by galvanometer driven scan mirrors starts in the upper left corner of the image and scans in the x-direction. At the end of the row the laser is switched off and the mirrors move back. The laser is switched on again and the scanning continues in the next row. This procedure is repeated up to the end of the image. The mirrors then move back to the starting position and the next image can be acquired. E, blow-up of the area containing the uncaging spot indicated in pink. For photolysis of NP-EGTA, the UV laser was switched on during the scanning process to illuminate the uncaging spot.