causes of physiological stress in shellfish
Lysosomes are regarded as valuable
indicators of compromised biotic integrity. Lysosomes, typically
involved in cellular defense, tissue repair and nutrition, can become
destabilized through exposure to a variety of stressors. This
assay is performed by incubating oyster hepatopancreas cells in neutral
red dye, then counting the number of cells with dye present in the
lysosomes (stable) or dye present in the cytosol (destabilized).
The leaking of neutral red reflects the efflux of lysosomal contents
into the cytosol, which ultimately leads to cell death.
Destabilized hepatopancreas cell
Higher percentages of lysosomal
destabilization indicate an adverse effect on the organism.
P-glycoprotein (p-gp) is a membrane
bound glycoprotein that acts as an efflux pump for organic
xenobiotics. P-gp has been found to be over-expressed in bivalves
collected at sites with high levels of organic pollution. Recent
work has focused on the effects of natural xenobiotics on p-gp
expression and activity (algal extracts have been shown to increase
p-gp expression; brevetoxin has been shown to affect p-gp
activity). This assay is performed using dot blot techniques and
antibody visualization to determine differences in p-gp expression
between individual oysters.
Higher expression or activity
of p-gp indicates an adverse effect on the organism.
In 2001, we found that
lysosomal destabilization was significantly elevated in native oysters
exposed to Kryptoperidinium sp. at the Kiawah 1 site. In
laboratory experiments, lysosomal destabilization was also
significantly elevated in hatchery-reared oysters exposed to Kryptoperidinium
bloom water for 4 days.
asterisk (*) indicates a significant difference from the control.
In 2002, hatchery-reared
oysters were deployed at the Kiawah 1 site, and were collected every
two weeks throughout the summer and fall. Lysosomal
destabilization rates were significantly related to Kryptoperidinium
concentrations, as was P-gp expression.
In 2003, Heterosigma akashiwo
blooms were collected from Bull’s Bay and Shem Creek.
Hatchery-reared oysters were exposed to this bloom water for 4 days,
with results similar to those of 2001. In both experiments,
lysosomal destabilization rates were higher in oysters exposed to bloom
water than control water. P-gp expression was also elevated after
exposure in the April 2003 experiment.
An asterisk (*)
indicates a significant difference from the same experimental
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