Targeted Mutations in the Na,K-ATPase Alpha 2 Isoform Confer Ouabain Resistance and Result in Abnormal Behavior in Mice

Sodium and potassium-activated adenosine triphosphatases (Na,K-ATPase) are ubiquitous, participate in osmotic balance and membrane potential, and are composed of alpha, beta, and gamma subunits. The alpha subunit is required for the catalytic and transport properties of the enzyme and contains binding sites for cations, ATP, and digitalis-like compounds including ouabain. There are four known alpha isoforms; three that are expressed in the CNS in a regional and cell-specific manner. The alpha 2 isoform is most commonly found in astrocytes, pyramidal cells of the hippocampus in adults, and developmentally in several other neuronal types. Ouabain-like compounds are thought to be produced endogenously in mammals, bind the Na, K-ATPase, and function as a stress-related hormone, however, the impact of the Na, K-ATPase ouabain binding site on neurobehavioral function is largely unknown. To determine if the ouabain binding site of the alpha 2 isoform plays a physiological role in CNS function, we examined knock-in mice in which the normally ouabain-sensitive alpha 2 isoform was made resistant (alpha 2(R/R)) while still retaining basal Na,K-ATPase enzymatic function. Egocentric learning (Cincinnati water maze) was impaired in adult alpha 2(R/R) mice compared to wild type (WT) mice. They also exhibited decreased locomotor activity in a novel environment and increased responsiveness to a challenge with an indirect sympathomimetic agonist (methamphetamine) relative to WT mice. The alpha 2(R/R) mice also demonstrated a blunted acoustic startle reflex and a failure to habituate to repeated acoustic stimuli. The alpha 2(R/R) mice showed no evidence of altered anxiety (elevated zero maze) nor were they impaired in spatial learning or memory in the Morris water maze and neither group could learn in a large Morris maze. These results suggest that the ouabain binding site is involved in specific types of learning and the modulation of dopamine-mediated locomotor behavior. Synapse 65: 520-531, 2011. (C) 2010 Wiley-Liss, Inc.