Meeting Abstract

69.4  Wednesday, Jan. 6  Localization of labile zinc in hemocyte lysosomes of the pond snail, Lymnaea stagnalis DIAMANT, A.G.*; RIDGWAY, R.L.; Seattle Pacific University; Seattle Pacific University adiamant@spu.edu

Hemocytes of Lymnaea stagnalis maintain normal cellular function when exposed to much higher (up to 10^-4 M) than ambient (10^-12 M to 10^-9 M) concentrations of ZnCl₂. While the ultimate destination of excess Zn²⁺ within the cell has remained an item of debate, previous studies in our lab suggest that Zn²⁺ is initially taken up endocytically in small “zincosomes” which then fuse with and/or mature into late endosomes and, eventually, lysosomes. To substantiate these findings, three competing hypotheses concerning the final site of sequestration of labile Zn²⁺ were tested: 1) exclusively lysosomes, 2) exclusively mitochondria, or 3) some combination of the two. Isolated hemocytes were labeled with FluoZin-3 AM (a membrane-permeant probe that fluoresces green upon binding Zn²⁺) and either LysoTracker Red DND-99 or MitoTracker Red FM (membrane-permeant probes that fluoresce red upon passively diffusing into their respective organelles). We observed and imaged the cells using a spinning disc confocal microscope in order to qualitatively evaluate the degree of co-localization between each organelle and Zn²⁺. To quantify the results, deconvolved images were analyzed and Pearson’s coefficients calculated. Results from a sample of 10 cells per experiment were used to calculate 95% confidence intervals, which suggest co-localization between lysosomes and Zn²⁺ (Pearson’s = 0.85 ± 0.03) and exclusion between mitochondria and Zn²⁺ (Pearson’s = 0.33 ± 0.06). These results support the specific hypothesis that Zn²⁺ is sequestered mainly, if not exclusively in the lysosomes. They also corroborate the more general hypothesis that the endosomal-lysosomal pathway is responsible for maintaining a low level of cytosolic labile Zn²⁺ in these cells. (Funded by a SPU Faculty Research Grant to RLR).