Pre-translational regulation of the (Na+ + K+)-ATPase in response to demand for ion transport in cultured chicken skeletal muscle.
The expression of the (Na+ + K+)-ATPase in cultured chicken skeletal muscle can be altered by varying the demand for ion transport. Veratridine, an activator of voltage-sensitive Na+ channels, causes a specific transient increase in biosynthesis of the sodium pump that accounts for the doubling of the number of (Na+ + K+)-ATPase molecules in the sarcolemma (Wolitzky, B.A., and Fambrough, D.M. (1986) J. Biol. Chem. 261, 9990-9999). Here we report a study of veratridine-induced up-regulation, focusing upon alpha- and beta-mRNA levels and transcription rates. Myotubes normally express the alpha 1-isoform mRNA and the beta-mRNA at a molar ratio of 0.6 +/- 0.1 (S.D.). In the presence of veratridine, the beta-mRNA is transiently up-regulated approximately 3-fold. The kinetics of this increase parallel the rate of beta-subunit protein synthesis. The increase in beta-mRNA during up-regulation is accomplished by an increase in the transcription rate of the beta gene. The veratridine-induced increase in beta-mRNA is not blocked by cycloheximide. The alpha-mRNA also increases during exposure to veratridine, but this increase is very modest and occurs very late in the up-regulation process. The increased beta-mRNA results in over-production of beta-subunits, which we postulate drives more efficient assembly of alpha beta complexes, i.e. sodium pump molecules. As the up-regulated state is achieved the level of beta-mRNA falls abruptly, reflecting a marked decrease in beta-mRNA stability. Treatment of up-regulated myotubes with tetrodotoxin, a veratridine antagonist, results in rapid down-regulation of the sodium pump, while having little or no effect on the levels of alpha 1- and beta-mRNAs.
Taormino
J P
JP
Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218.
Fambrough
D M
DM
D000818:Animals; D001692:Biological Transport; D015152:Blotting, Northern; D002462:Cell Membrane / Q000201:enzymology; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D002642:Chick Embryo; D015971:Gene Expression Regulation, Enzymologic; D007700:Kinetics; D046911:Macromolecular Substances; D009132:Muscles / Q000201:enzymology*; D014176:Protein Biosynthesis; D012313:RNA / Q000235:genetics / Q000302:isolation & purification; D012333:RNA, Messenger / Q000235:genetics; D000254:Sodium-Potassium-Exchanging ATPase / Q000096:biosynthesis / Q000235:genetics*; D014158:Transcription, Genetic
D046911:Macromolecular Substances; D012333:RNA, Messenger; D012313:RNA; D000254:Sodium-Potassium-Exchanging ATPase