Na+/K+ ATPase ?1 and ?3 isoforms are differentially expressed in ?- and ?-motoneurons.

ABSTRACT: The Na(+)/K(+) ATPase (NKA) is an essential membrane protein underlying the membrane potential in excitable cells. Transmembrane ion transport is performed by the catalytic ? subunits (?1-4). The predominant subunits in neurons are ?1 and ?3, which have different affinities for Na(+) and K(+), impacting on transport kinetics. The exchange rate of Na(+)/K(+) markedly influences the activity of the neurons expressing them. We have investigated the distribution and function of the main isoforms of the ? subunit expressed in the mouse spinal cord. NKA?1 immunoreactivity (IR) displayed restricted labeling, mainly confined to large ventral horn neurons and ependymal cells. NKA?3 IR was more widespread in the spinal cord, again being observed in large ventral horn neurons, but also in smaller interneurons throughout the dorsal and ventral horns. Within the ventral horn, the ?1 and ?3 isoforms were mutually exclusive, with the ?3 isoform in smaller neurons displaying markers of ?-motoneurons and ?1 in ?-motoneurons. The ?3 isoform was also observed within muscle spindle afferent neurons in dorsal root ganglia with a higher proportion at cervical versus lumbar regions. We confirmed the differential expression of ? subunits in motoneurons electrophysiologically in neonatal slices of mouse spinal cord. ?-Motoneurons were excited by bath application of low concentrations of ouabain that selectively inhibit NKA?3 while ?-motoneurons were insensitive to these low concentrations. The selective expression of NKA?3 in ?-motoneurons and muscle spindle afferents, which may affect excitability of these neurons, has implications in motor control and disease states associated with NKA?3 dysfunction.

SUBMITTER: Edwards IJ 

PROVIDER: S-EPMC3722489 | biostudies-literature | 2013 Jun

REPOSITORIES: biostudies-literature