title: Ionic mechanisms of excitation-induced regulation of Na+-K+-ATPase mRNA expression in isolated rat EDL muscle.
abstract: This study investigated the effects of electrical stimulation on Na+-K+-ATPase isoform mRNA, with the aim to identify factors modulating Na+-K+-ATPase mRNA in isolated rat extensor digitorum longus (EDL) muscle. Interventions designed to mimic exercise-induced increases in intracellular Na+ and Ca2+ contents and membrane depolarization were examined. Muscles were mounted on force transducers and stimulated with 60-Hz 10-s pulse trains producing tetanic contractions three times at 10-min intervals. Ouabain (1.0 mM, 120 min), veratridine (0.1 mM, 30 min), and monensin (0.1 mM, 30 min) were used to increase intracellular Na+ content. High extracellular K+ (13 mM, 60 min) and the Ca2+ ionophore A-23187 (0.02 mM, 30 min) were used to induce membrane depolarization and elevated intracellular Ca2+ content, respectively. Muscles were analyzed for Na+-K+-ATPase alpha1-alpha3 and beta1-beta3 mRNA (real-time RT-PCR). Electrical stimulation had no immediate effect on Na+-K+-ATPase mRNA; however at 3 h after stimulation, it increased alpha1, alpha2, and alpha3 mRNA by 223, 621, and 892%, respectively (P = 0.010), without changing beta mRNA. Ouabain, veratridine, and monensin increased intracellular Na+ content by 769, 724, and 598%, respectively (P = 0.001) but did not increase mRNA of any isoform. High intracellular K+ concentration elevated alpha1 mRNA by 160% (P = 0.021), whereas A-23187 elevated alpha3 mRNA by 123% (P = 0.035) but reduced beta1 mRNA by 76% (P = 0.001). In conclusion, electrical stimulation induced subunit-specific increases in Na+-K+-ATPase mRNA in isolated rat EDL muscle. Furthermore, Na+-K+-ATPase mRNA appears to be regulated by different stimuli, including cellular changes associated with membrane depolarization and increased intracellular Ca2+ content but not increased intracellular Na+ content.
authors.affiliation: School of Human Movement, Recreation and Performance, Centre for Ageing, Rehabilitation and Sport Science, Victoria University of Technology, Melbourne, Australia. km@fi.au.dk
authors.forename: K T
authors.initials: KT
authors.lastname: Murphy
authors.forename: W A
authors.initials: WA
authors.lastname: Macdonald
authors.forename: M J
authors.initials: MJ
authors.lastname: McKenna
authors.forename: T
authors.initials: T
authors.lastname: Clausen
mesh_terms: D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D007473:Ion Channels / Q000502:physiology*; D007476:Ionophores / Q000494:pharmacology; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D008985:Monensin / Q000494:pharmacology; D009470:Muscle Spindles / Q000502:physiology; D018482:Muscle, Skeletal / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis*; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012964:Sodium / Q000378:metabolism / Q000502:physiology; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics; D014701:Veratridine / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D007473:Ion Channels; D007476:Ionophores; D007527:Isoenzymes; D012333:RNA, Messenger; D000001:Calcimycin; D010042:Ouabain; D014701:Veratridine; D008985:Monensin; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium