Quantitative ultrastructure of gill epithelial cells in the larval lampreyPetromyzon marinus

Abstract

Cells and organelles in the respiratory epithelium of the sea lamprey (Petromyzon marinus) gill were measured in electron micrographs of plastic-embedded sections to provide baseline data for future quantitative studies of how toxicants affect gill morphology. Stereology was used, based on the [Formula: see text] method for determining cell volumes. The method was checked against unbiased methods and was shown to be accurate within 12%. We found that cells in the basal layer of the epithelium, basal cells, are smaller (averaging 338 μm3) and contain smaller volumes of most organelles, than cells in the superficial layer. These features suggest that basal cells are either undifferentiated or differentiating cells. The superficial layer contains larger, more specialized cells: presumed ion-uptake cells (817 μm3) and mucous-pavement cells (548 μm3). Ion-uptake cells contain the largest volume of mitochondria (270 μm3), consistent with the high energy demands of ion transport. Mucous-pavement cells contain the largest volume of secretory vesicles (55 μm3), presumably for coating the lamellae with protective mucus. A new cell type was discovered, with features intermediate between basal cells and mucous-pavement cells, suggesting that the former cells transform into the latter. Volumes of gill epithelial cells are independent of animal size.