STIMULATION OF NA-K+-ATPASE BY THYROTROPIN IN CULTURED THYROID FOLLICULAR CELLS()

Thyroid-stimulating hormone (TSH; thyrotropin) produces a pleiotropic response in the thyroid gland, accelerating nearly every aspect of met abolic turnover within the follicular epithelia. We examined the effec ts of TSH on expression of Na+-K+-ATPase in FRTL-5 cells, a cell line derived from rat thyroid. TSH (10 mU/ml) produced a nearly twofold inc rease in abundance of the mRNA encoding the catalytic alpha(1)-subunit within 6 h of treatment. With the four mRNAs encoding the beta(1)-sub unit, TSH produced a striking increase in abundance, but this regulati on was discoordinate, and some species increased more than others. Sim ilar increases in mRNA abundance were elicited by activators of the ad enosine 3',5'-cyclic monophosphate second messenger system. In contras t to the alpha(1)- and beta(1)-mRNAs, the abundance of the mRNA encodi ng the beta(2)-subunit was unchanged with TSH after 6 h, indicating th at the effects of thyrotropin were not universal or indiscriminate. Th yrotropin also caused a 76% increase in Na+-K+-ATPase activity and a 4 6% increase in pump-mediated transport after 48 h. These studies sugge st that the changes in metabolic turnover initiated by TSH during horm one synthesis include upregulation of the Na+-K+ pump.