Molecular isoforms of the sodium pump in brain

The Na+,K+-ATPase is a basic membrane element in all animal cells that maintain transmembrane gradients of Na+ and K+ ions. When integrated into artificial lipid vesicles the isolated Na+,K+-ATPase is capable of actively transporting Na+ and K+, thus establishing its identity with the well-known Na+ pump. Three isoforms of the catalytic subunit of Na+,K+-ATPase have recently been identified in the rat brain. Elucidating the regulatory processes which govern their biosynthesis in the brain is central to understanding the physiological alterations which accompany diabetes, chronic cardiotonic steroid intoxication and degenerative diseases of the retina. In this study, synthesis of the alpha-1 and alpha-2 isoforms was examined in the retina of rats following intraocular injection of citrate buffer. Incorporation of [35S]methionine into both isoforms was increased 60-100% by 6 hr, demonstrating that neuronal Na+ pump is subject to regulation, although the question of independent regulatory controls remains unanswered.