The Canine Cardiac α3 Isoform of Na+/K+-ATPase is Highly Sensitive to Digitoxigenin
Three alpha (α1, α2, α3) and three beta (ß1, ß2, ß3) subunits of Na+/K+-ATPase have been identified from cDNA cloning (9). The expression of only α1 isoform has been shown in the kidney in all the mammalian species considered. In the brain, two other isoforms (α2 and α3) are concomitantly expressed (as reviewed in 15). However, each of them can be expressed separately in other tissues such as: α2 in the cardiac and skeletal muscles and α3 in the pineal gland (14), and macrophages (16). In dog heart, we have previously reported the existence of α1 and α+ isoforms. Since it was immunologically demonstrated that the α+ form could contain a mixture of α2 and; α3 isoforms (15), it was our objective to further investigate in dog heart and brain the nature and function of these two isoforms. We have used the panel of antibodies specific for the three rat α subunit isoforms (13) in Western blot analysis of canine microsomal fractions from kidney, brain and heart. In fliese 3 tissues, functional differences were investigated in terms of sensitivity to digitoxigenin (DGN) and Na+since differences in Na+ affinity have also been associated with isoform properties (4–7, 14).
KeywordsElectrophoresis Vanadate Polypeptide NADH Digoxin
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