Journal of Electron Microscopy Advance Access published online on February 25, 2009
Journal of Electron Microscopy, doi:10.1093/jmicro/dfp010
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Exposure of the gill epithelial cells of larval lampreys to an ion-deficient environment: a stereological study
1 Anatomische Anstalt, Ludwig-Maximilians-Universität München, 80336 München
2 Zentrum Anatomie, Medizinische Hochschule Hannover, 30625 Hannover, Germany
3 Centre for Fish and Fisheries Research, School of Biological Sciences and Biotechnology, Murdoch University, Murdoch 6150, Western Australia, Australia
* To whom correspondence should be addressed. E-mail: helmut.bartels{at}med.uni-muenchen.de
Three kinds of epithelial cells comprise the surfaces of the gill filaments and lamellae of larval lampreys (ammocoetes): ammocoete mitochondria-rich cells (AMRCs), intercalated mitochondria-rich cells (IMRCs) and pavement cells. Selected characteristics of these cell types in ammocoetes of Geotria australis held in distilled water and in 10% sea water were compared using an ultrastructural stereological approach to determine which of those cell type(s) respond to exposure to an ion-deficient environment in a manner that indicates that they are involved in ion uptake. Particular focus was placed on the enigmatic AMRC, which comprises ca 60% of the cells and contains numerous mitochondria. The mean percentage contributions of both AMRCs and pavement cells to the total number of the three cell types in the two experimental groups were not significantly different, whereas that of IMRCs was >7% in distilled water and <1% in 10% sea water (P < 0.001). Furthermore, the mean apical surface areas of neither AMRCs nor pavement cells differed significantly between the two experimental groups, whereas that of IMRCs was nearly 3-fold greater in distilled water than in 10% sea water. The volume densities and size of mitochondria in AMRCs did not differ between the two exposure regimes. The above comparisons provide no indications that the uptake of Na+ and Cl– in the gill epithelium of ammocoetes involves either the AMRC or pavement cell but, when considered in conjunction with data on ion-transporting cells in other vertebrates, they are consistent with the conclusion that the IMRC plays a crucial role in this process.
Keywords mitochondria-rich cells, gill epithelium, lampreys, ionic regulation, fresh water
Received 31 August 2008, accepted 4 February 2009