A single isoform of the Na+/K+‐ATPase α‐subunit in Diptera: evidence from characterization of the first extracellular domain

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Abstract
The first extracellular domain of the α‐subunit of the Na+/K+‐ATPase (sodium/potassium pump) is functionally important, affecting sensitivity of the enzyme to cardiac glycosides (e.g. ouabain) and being implicated in the transport of K+. This domain is also variable among mammalian isoforms of the α‐subunit. Using PCR, we have isolated from seven insect species with contrasting physiologies a DNA fragment containing this region, in order to help determine whether tissue‐specific expression might be associated with isoforms encoded by a gene family, as it is in mammals. A single sequence (with one ORF) characteristic of Na+/K+‐ATPase was obtained from genomic DNA of each species. Only the fragment from Manduca sexta contained an intron, but at a location different to that found in mammals. For all Diptera so far characterized, the species phylogeny is the same as the α‐subunit gene phylogeny (based on the sequences of the first extracellular domain and flanking transmembrane domains). The results strongly indicate a single, ouabain‐sensitive isoform of the α‐subunit of Na+/K+‐ATPase is present in Diptera.