Mechanisms of acid secretion in pseudobranch cells of rainbow trout Oncorhynchus mykiss

摘要

Cell suspensions of rainbow trout Oncorhynchus mykiss pseudobranch, prepared by Ca2+ depletion and mechanical maceration, contained a distinct population of cells that always kept their relatively cuboidal shape and did not round up in suspension or proliferate after adhering to the surface of cell culture dishes. Phase-contrast microscopy revealed an extensive system of basal membrane invaginations, and Na+-K+-ATPase- and anion-exchanger-like immunoreactivity could be localized in cell membranes. The cells were characterized by a high mitochondrial density. Using specific antibodies, V-ATPase subunit B was localized in the plasma membrane. Using a cytosensor microphysiometer, the rate of acid secretion of these cells was measured and compared with the activity of a gill cell preparation. Incubation of pseudobranch cells with bafilomycin A1 (10(-6)mol l(-1)), a specific inhibitor of V-ATPase, reduced the rate of acid secretion by about 10% under control conditions, while no effect of bafilomycin on the rate of acid secretion of gill cells was observed. Application of amiloride (5X10(-5) mol l(-1)) reduced the rate of acid secretion in cells of both organs, pseudobranch and gills. Incubation of pseudobranch cells with DIDS (10(-3) mol l(-1)) resulted in a minor increase in the rate of proton secretion, but in cells prepared from the gills of rainbow trout acid secretion was reduced by about 30-40%. It is concluded that pseudobranch cells are equipped with various pathways to secrete protons, and that the anion exchange activity especially of pseudobranch cells appears to be different from that in gills. [References: 48]