Molecular cloning and characterization of two Na/K-ATPase isoforms in Fundulus heteroclitus

Na/K-ATPase plays an important role in ion regulation in teleost fishes. In most taxa several isoforms exist to provide physiological versatility to specific cell types, but little is known about Na/K-ATPase isoforms in fish. A reverse transcriptase polymerase chain reaction approach was used to identify Na/K-ATPase a-subunit isoforms from the gill and muscle of an estuarine teleost, Fundulus heteroclitus. Full-length complementary DNA sequences were similar at both the nucleotide level (74.4%) and the amino acid level (82.5%). Phylogenetic analysis indicated that the gill isoform was similar to the mammalian a1 subunit and the muscle isoform was similar to the mammalian a2 subunit. Northern blotting and isoform-specific polymerase chain reaction were used to determine the tissue distribution of the isoforms. The gill (a1) isoform was expressed in all tissues, while the muscle (a2) isoform had a much more restricted expression pattern, being present at high levels only in muscle and brain, consistent with the distributions of these isoforms in mammals.