Abstract
Na,K-ATPase activity, Na,K-ATPase alpha- and beta-subunit mRNA abundance (mRNA alpha and mRNA beta), and gene transcription rates were determined in kidney cortex and liver of hypothyroid and triiodothyronine (T3)-treated rats. In hypothyroid rats, Na,K-ATPase activity (expressed per unit of DNA) was 3.6-fold greater in kidney cortex than liver, and the abundance of mRNA alpha and mRNA beta in kidney cortex exceeded that of liver by 2.8- and 5.2-fold, respectively. In vitro nuclear run-on analysis revealed similar rates of Na,K-ATPase alpha and beta gene transcription in nuclei isolated from either kidney cortex or liver. Administration of T3 for 72 h elicited a 2.3-fold stimulation of renal Na,K-ATPase activity that was associated with a 3.1- and 2.6-fold increase of mRNA alpha and mRNA beta content, respectively. In contrast, T3 induced a 1.3-fold stimulation of liver Na,K-ATPase activity accompanied by a 7.3-fold increase in mRNA alpha and no change in mRNA beta abundance. Transcription rates of alpha and beta genes (assayed by nuclear run-on) in renal cortex were both stimulated 1.8-fold in response to T3 injection. Similarly in liver nuclei, T3 treatment produced a 1.4- and 1.3-fold stimulation in the rate of alpha and beta gene transcription, respectively. These results indicate that significant discrepancies exist in the quantitative relationships between control and T3-induced changes in renal and hepatic enzyme activity, mRNA abundance and rate of gene transcription, and imply that the T3-induced increase in Na,K-ATPase abundance is mediated at both transcriptional and post-transcriptional steps.
Highlights
Na,K-ATPase activity, Na,K-ATPase a- and &subunit mRNA abundancea, nd gene transcription rates were determined inkidney cortex and liver of hypothyroid and triiodothyronine (Ts)treated rats
We recently demonstrated,that tionships between control and Ts-induced changes in stimulation of Na,K-ATPase activity in rat renal cortex and renal and hepaticenzyme activity, mRNA abundance ventricular myocardium by T3is associated with augmentaand rateof gene transcription, andimply that theTsinduced increase in Na,K-ATPase abundance is mediated at both transcriptional and post-transcriptional steps
DNA content/unit of tissue weight rose and inkidney cortex fell in response to T3
Summary
To establish a reference standard for the effect of T3 on Na,K-ATPase activity or expression of the a and ,8 genes in rat kidney cortex and liver, we evaluated the effect of T3 on tissue protein, DNA, and RNA content (Table I). Enzyme Actiuities-In confirmation of previous results, Na,K-ATPase activity (expressed/mg of protein) was augmented 1.6- and 1.4-fold in renal cortex and liver homogenates, respectively, in response to T3 (Table 11) [10, 14, 22]. Hybridization of a replicate kidney cortex RNA blot with 32P-labeledrat brain cDNA0 revealed a predominate and a minor RNA band migrating at 22 S and 18 S, respectively These mRNA bands are consistent with previous descriptions of tissue-specific expression of multiple forms of mRNAB[45].
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