Peanut lectin binds to a subpopulation of mitochondria-rich cells in the rainbow trout gill epithelium

Fluorescently labeled peanut lectin agglutinin (PNA-FITC) was used to ident ify a subtype of mitochondria-rich (MR) cells in the gills of freshwater ra inbow trout. In situ binding of PNA-FITC was visualized by inverted fluores cence microscopy and found to bind to cells on the trailing edge of the fil ament epithelium as demonstrated by differential interference contrast opti cs. The amount of PNA-FITC binding on the filament epithelium increased wit h cortisol pretreatment concomitant with an increased chloride cell fractio nal area as demonstrated by scanning electron microscopy. Dispersed gill ce lls were isolated by trypsinization and separated using a discontinuous Per coll density gradient. Cells migrating to the 1.06-1.09 g/ml interface were found to be MR as demonstrated by staining with the vital mitochondrial dy e 4-(4-(dimethylamino)styryl)-N-methylpyridinium iodide and transmission el ectron microscopy (TEM). However, only similar to 40% of the MR cells were found to bind PNA-FITC. Cortisol pretreatment increased the relative number s of MR cells isolated from the dispersed gill cell population, but the rel ative proportions of PNA binding cells remained unchanged. Ultrastructural analysis of isolated cells in the TEM demonstrated that the MR cell fractio n was comprised of a mixed population of chloride cells and pavement cells.