Responsiveness of alpha 1 and beta 1 cochlear Na, K-ATPase isoforms to thyroid hormone.

The effects of thyroid hormone on Na, K-ATPase subunit isoforms under euthyroid (EUTH), hypothyroid (HYPO) and hyperthyroid (HYPER) states were investigated via immunocytochemistry and the use of polyclonal antibodies specific to each isoform (alpha 1, alpha 2, alpha 3 and beta 1, beta 2). In HYPO animals, there was a distinct decrease in Na, K-ATPase alpha 1 isoform immunoreactivity in the stria vascularis (SV), spiral ganglion (SG) cells, spiral limbus (SLi) and cochlear nerve (CN) as compared with that in EUTH animals by the 17th day of the experiment. Immunostaining of the alpha 1 isoform increased in HYPER animals as compared with that in HYPO animals, and reached a level comparable to that in EUTH animals after 2 days of triiodothyronine (T3) treatment. Levels of alpha 2, alpha 3 and beta 2 isoforms did not appear to be affected by T3 administration. By the 19th day of a low I2 diet, the immunoreactive intensity of the beta 1 isoform was reduced in cochlear tissues of HYPO animals as compared with that in EUTH animals. The immunoreactivity of the beta 1 isoform increased after treatment with T3 for 4 days and was comparable with levels in EUTH animals. These data indicate that alpha 1 and beta 1 isoforms within specific cochlear regions of the adult rat are responsive to thyroid hormone.