FIGURE 1.

Effect of Ca²⁺-releasing messengers on Mn²⁺-mediated quenching of fura-2 trapped in the lumen of yolk platelets. Yolk platelets are lysosome-related organelles in sea urchin eggs. A, addition of 100 μm MnCl₂ rapidly decreases fluorescence. The gray box highlights the area expanded in panel B. B, basal rate of fura-2 quenching is accelerated by NAADP (500 nm) and ionomycin (5 μm) but not a second addition of NAADP (500 nm) or inositol 1,4,5-trisphosphate (10 μm) or cADP-ribose (1 μm). C, the effect of a messenger is not affected by the order of addition (concentrations as in B). D, pre-treatment with a low concentration of NAADP (5 nm) abolishes the subsequent response to supramaximal NAADP (500 nm) demonstrating diagnostic self-desensitization. Other concentrations are as in panel B.