Isoforms of Na,K-ATPase a and b Subunits in the Rat Cerebellum and in Granule Cell Cultures

There are multiple isoforms of the Na,K-ATPase in the nervous system, three isoforms of the a subunit, and at least two of the b subunit. The a subunit is the catalytic subunit. The b subunit has several roles. It is required for enzyme assembly, it has been implicated in neuron-glia adhesion, and the experimental exchange of b subunit isoforms modifies enzyme kinetics, implying that it affects functional properties. Here we describe the specificities of antibodies against the Na,K-ATPase b subunit isoforms b1 and b2. These antibodies, along with antibodies against the a subunit isoforms, were used to stain sections of the rat cerebellum and cultures of cerebellar granule cells to ascertain expression and subcellular distribution in identifiable cells. Comparison of a and b isoform distribution with doublelabel staining demonstrated that there was no preferential association of particular a subunits with particular b subunits, nor was there an association with excitatory or inhibitory neurotransmission modes. Isoform composition differences were seen when Purkinje, basket, and granule cells were compared. Whether b1 and b2 are specific for neurons and glia, respectively, has been controversial, but expression of both b subunit types was seen here in granule cells. In rat cerebellar astrocytes, in sections and in culture, a2 expression was prominent, yet the expression of either b subunit was low in comparison. The complexity of Na,K-ATPase isoform distribution underscores the subtlety of its regulation and physiological role in excitable cells.