MOLUSKUEN LISERI-GURUINEKO EPITELIOAREN ... - Euskara

Emaitzak eta eztabaida
Cell-type replacement in the digestive gland of mussels exposed to
pollutants
Abstract: The digestive gland epithelium of the mussel Mytilus galloprovincialis (Lmk) is comprised of
two cell types, namely digestive and basophilic cells. Under normal circumstances digestive cells
outnumber basophilic cells but under the influence of pollutants a relative increase in the proportion of
basophilic cells has been described. This alteration has been termed cell-type replacement (CTR).
Autometallography (AMG) is a sensitive histochemical technique to localize metals in cells as black silver
deposits (BSD) and has been used in the assessment of environmental metal pollution. BSD are localized
in the digestive cells lysosomes. The objectives of this work are three. First, to know whether pollutants such
as Cd were able to induce CTR. Second, to check wether Cd localization revealed by AMG at the
ultrastructural level were cell-specific and, if so, to determine wether CTR influenced the estimations made
by AMG. Finally, to determine the effective concentration of various pollutants to provoke CTR and to check
wether CTR is reversible. For these purposes mussels were exposed to different concentrations of organic
and inorganic pollutants at various exposure-times in five complementary laboratory experiments. In order
to quantify CTR, volume density of basophilic cells (Vv BAS ) was estimated on hematoxylin-eosin stained
sections by means of stereology. Similarly, the volume density of BSD (Vv BSD ) was calculated with the aid
of an image analysis. Results revealed that Cd provoked CTR. On the other hand, while BSD were
specifically localized within digestive cells lysosomes, basophilic cells were devoid of BSD. X-ray
microprobe analisys and X-ray mapping demonstrated that although BSD are not metal specific they were
mainly formed around the Cd associated to S atoms. Due to this specific localization, CTR influences
Vv BSD values, and therefore when environmental bioavailable metal levels are estimated this must be
taken into account. On the other hand, organic and inorganic pollutants or their mixtures can provoke CTR
although critical concentrations may change.
Key Words cell-type replacement, autometallography, cadmium, benzo(a)pyrene, X-ray microanalysis,
mussel, digestive gland.
78