An ouabain-insensitive mechanism of cell volume maintenance, similar to that operating in the kidney tissue of mammals and in epithelial cells of the frog urinary bladder, has been demonstrated in the kidney tissue of carp (Cyprinus carpio)--there is no significant swelling even after 4-hour incubation with 10(-4) mol/l-1 ouabain. 2) The mechanism is not affected by 2-hour incubation with sodium in the saline replaced with tris or choline and, unlike in rabbit kidney cortex, cannot be inhibited by alkaline pH. 3) Neither a contractile mechanism sensitive to cytochalasin B, nor transport of divalent cations could be shown to be involved in this ouabain-insensitive cell volume maintenance in the carp kidney tissue.
