Localization of Na, K-ATPase Isoforms in the Hypothalamus of the Rat

In situ hybridization histochemistry with synthetic oligonucleotide probes was used to localize mRNAs encoding three isoforms of the catalytic (alpha) subunit and one isoform of the (beta) subunit of the Na, K-ATPase in rat hypothalamus using contact film radioautography. 3H-Ouabain binding to specific anatomical nuclei in the hypothalamus was determined using a quantitative radioautographic technique previously developed in our laboratory. Specific hybridization was found with oligonucleotide probes for mRNA encoding alpha 1, alpha 2, alpha 3, beta 1 isoforms of the Na, K-ATPase. High levels of hybridization signal for alpha 3 and beta 1 were found in ventromedial hypothalamus, supraoptic nucleus, paraventricular nucleus and the anterior hypothalamic area. Very low levels of hybridization for all isoforms were found in the optic chiasm. mRNAs encoding alpha 1 and alpha 2 isoforms were expressed at lower levels than alpha 3. The distribution of alpha 2 was consistent with expression in glial cells. Generally, levels of alpha 1 mRNA were higher in the arcuate nucleus than in other hypothalamic regions and very low levels were found in the anterior hypothalamic area. 3H-Ouabain binding was relatively diffuse, consistent with the localization of the synthesized Na, K-ATPase protein in cellular processes. The number of 3H-ouabain binding sites in the paraventricular nucleus was significantly lower than other hypothalamic nuclei studied. The results suggest that Na, K-ATPase isoforms may be differentially expressed in hypothalamic nuclei.