Regulation of Intracellular Sodium
The sodium pump is particularly abundant in the brain.
Na+,K+-ATPase,
uses approximately 50% of oxygen consumption in the brain. In addition to its
housekeeping role the enzyme is essential for the maintenance of ionic
gradients of Na and K, that underline the resting and the action potentials
and neuronal excitability. The sodium pump consists of catalytic alpha and
regulatory beta subunits. Three isoforms of alpha and two of beta subunits of
the
Na+,K+-ATPase
have been identified in mammalian cells. All tissues express alpha-1 and
beta-1 isoforms. The alpha-2 subunit is found mainly in skeletal muscle
and heart, whereas alpha-3 is predominantly detected in neurones. Neurones
express both alpha-3 (presumably mainly in axons) and alpha-1 (presumably
mainly in dendrites). Interestingly, studies on purified enzyme have indicated
that alpha-1 has higher Na affinity than alpha-3. Thus, alpha-3 would
allow for a higher intracellular Na concentration than alpha-1.