Isoform expression of Na+-K+-ATPase alpha-subunit in gills of the teleost Oreochromis mossambicus

Abstract

Three isoform-specific antibodies, 6F against the alpha(1)-isoform of the avian sodium pump, HERED against the rat alpha(2)-isoform, and Ax2 against the rat alpha(3)-isoform, were used to detect the expression of Na+-K+-ATPase alpha-subunits in gills of a teleost, the tilapia (Oreochromis mossambicus). Tilapia gill tissue showed positive reactions to antibodies specific for alpha(1)- and alpha(3)-sofoonms. The results of immunoblots were converted to numerical values (relative intensities) by image analysis for comparisons. Relative amounts of alpha(1)-like isoform alone and consequently the ratio of alpha(1)-like to alpha(3)-like isoforms were higher in gills of seawater-adapted tilapia than in those of freshwater-adapted ones, indicating that the two isoforms respond differently to environmental salinities. In the subsequent immunocytochemical experiments, gill mitochondria-rich cells were demonstrated to immunoreact with antibodies specific for alpha(1)- and alpha(3)-isoforms. alpha(1)-like and alpha(3)-like isoforms of gill Na+-K+-ATPase are suggested to be involved in the ion- and osmoregulation mechanisms in tilapia. Moreover, differential expressions of two isoforms may be associated with different functions, secretion and uptake of ions and acid-base regulation, in gills of seawater- and freshwater-adapted tilapia.