DEMONSTRATION OF CALCIUM-UPTAKE AND RELEASE BY SEA-URCHIN EGG CORTICAL ENDOPLASMIC-RETICULUM

The calcium indicator dye fluo-3/AM was loaded into the ER of isolated cortices of unfertilized eggs of the sea urchin Arbacia punctulata. Development of the fluorescent signal took from 8 to 40 min and usually required 1 mM ATP The signal decreased to a minimum level within 30 s after perfusion with 1-mu-M InsP3 and increased within 5 min when InsP3 was replaced with 1 mM ATP. Also, the fluorescence signal was lowered rapidly by perfusion with 10-mu-M A23187 or 10-mu-M ionomycin. These findings demonstrate that the cortical ER is a site of ATP-dependent calcium sequestration and InsP3-induced calcium release. A light-induced wave of calcium release, traveling between 0.7 and 2.8-mu-m/s (average speed 1.4-mu-m/s, N = 8), was sometimes observed during time lapse recordings; it may therefore be possible to use the isolated cortex preparation to investigate the postfertilization calcium wave.