Demonstration of calcium uptake and release by sea urchin egg cortical endoplasmic reticulum

Abstract. The calcium indicator dye f luo-3 /AM was loaded into the ER of isolated cortices of unferti l ized eggs of the sea urchin Arbacia punctulata. Develop-ment of the f luorescent signal took from 8 to 40 min and usual ly required 1 mM ATP The signal decreased to a minimum level within 30 s after perfusion with 1 FAM InsP3 and increased within 5 min when InsP3 was replaced with 1 mM ATP. Also, the f luorescence sig-nal was lowered rapidly by perfusion with 10 p,M NTRACELLULAR free calcium rises near the sperm entry point in the eggs of many animals; a wave of elevated calcium then proceeds from this region by a release of calcium from internal stores (Gi lkey et al., 1978; Jaffe, 1983; Hafner et al., 1988). The calcium wave is crucial in the activation of the egg (Whitaker and Steinhardt, 1982