Ultrastructural effects of 3-trifluormethyl-4-nitrophenol on gills of the larval lamprey <i>Petromyzon marinus</i>

Abstract

Lamprey larvae (ammocoetes) are susceptible to 3-trifluormethyl-4-nitrophenol (TFM), a lampricidal toxicant which is administered through the ambient water. While this organic acid readily diffuses across gill cytomembranes, its actual mode of toxicity is uncertain. In this ultrastructural study, we examined the gills of larval Petromyzon marinus exposed to a nearly lethal dose (2.25 mg/L for 9 h, which is a median lethal concentration). Toxicant-associated damage was limited almost exclusively to a single gill epithelial cell type: presumed ion-uptake cells. These mitochondria-rich cells, which in normal ammocoete gills constitute the major portion of the respiratory surface, showed ultrastructural alterations ranging from abnormalities in microvilli and (or) cytoplasmic vacuolization to hypertrophy or even cytolysis. TFM-poisoned gills also differed from controls in having widened intercellular spaces within both respiratory lamellar epithelium and branchial interlamellar epithelium. Such intercellular spaces were particularly large in the vicinity of ion-uptake cells. These findings are consistent with a proposal that fish branchial ion-pumping cells function in extracting and extruding blood-borne organic acids, yet succumb to the damaging effects of such acids when intracellular concentrations exceed certain levels.