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(88-04) Cell-type replacement in molluscan digestive gland: role of basophilic cells in adaptation to chronic pollution. Marigomez, Ionan*,1, Zaldibar, Beņat1, Cancio, Ibon1, Soto, Manu1, Cajaraville, Miren1, 1 Cell Biology & Histology Lab, Zool. & Animal Cell Dynamics Dept., Univ. Basque Country, P.O.BOX 644, Bilbo, Basque Country, Basque Country ABSTRACT- Biomarkers are pollutant-induced changes considered as early warning signals that can predict changes at complex biological levels. Laboratory and field studies demonstrate that the molluscan digestive gland responds to environmental insult, particularly after short-term exposures to high (sublethal) pollutant levels. Occasionally, inconsistent results are reported after long-term exposure in the laboratory and after chronic pollution episodes in the field. Physiological and genetic adaptations have been widely proposed to explain controversial findings but experimental evidence is lacking. Our observations suggest that adaptation might result from developmental processes (reversible plasticity) that give rise to altered cell type composition. Thus, whereas in laboratory controls and field clean sites digestive cell (target cell-type for most biomarkers) is the most abundant cell-type in the digestive gland epithelium, in episodes of long-term and chronic pollution basophilic cells outnumber digestive cells. Even more, these basophilic cells appear to be hyperplastic. Cell type replacement would depend on the particular proliferating capacities of each cell-type and, interestingly, is readily reversible after ceasing environmental insult. Obviously both biochemistry and physiology of the digestive gland are dramatically different from those reported in conditions of short-term experimentation. The role of basophilic cells in adaptation to chronic pollution and the physiological, toxicological and ecological consequences of cell-type replacement are discussed. How the use of biomarkers is affected by such apparently successful strategy to adapt to chronic pollution is also discussed. Particular emphasis is given to discuss that biochemical and physiological biomarker approaches overlook the fact that most biomarkers are based on cell-type specific responses and cannot anyhow discriminate specific biomarker responses or alterations due to changes in cell-type composition. * Research Project funded by the Basque Government (PI 99-023). Key words: molluscan digestive gland, cell-specific biomarkers, chronic pollution, adaptation |
