Distribution and Characterization of Ion Transporting and Respiratory Filaments in the Gills of Procambarus clarkii

Individual gill filaments of the freshwater crayfish Procambarus clarkii were determined to be either predominantly respiratory or transporting. Silver staining revealed that the filaments within the central bed of the gills formed silver deposits whereas filaments at the margins and the entire sixth pleurobranch formed no deposits. Designation of the silver staining gills as predominantly transporting and unstained filaments as predominantly respiratory was substantiated by ultrastructural analyses and measurements of ATPase and transepithelial potentials. Presumptive transporting filaments had an epithelium subjacent to the cuticle that was relatively thick and dominated by abundant mitochondria. Lacunae were delineated by pillar structures and served as collateral pathways for the movement of blood from the afferent to efferent blood channels, which were separated by a thin septum. Presumptive respiratory filaments had an extremely thin epithelium with few organelles, but a relatively thick septum. Present in both types of filaments were nerves and podocytes. The values for Na, K-ATPase were significantly higher in the transporting filaments than in those designated as respiratory. The measurement of transepithelial potentials showed both filaments to be cation selective with the respiratory filaments slightly more positive and the transporting filaments slightly more negative than the diffusion potential for Na.