title: Cytosolic calcium transients are a determinant of contraction-induced HSP72 transcription in single skeletal muscle fibers.
abstract: The intrinsic activating factors that induce transcription of heat shock protein 72 (HSP72) in skeletal muscle following exercise remain unclear. We hypothesized that the cytosolic Ca(2+) transient that occurs with depolarization is a determinant. We utilized intact, single skeletal muscle fibers from Xenopus laevis to test the role of the cytosolic Ca(2+) transient and several other exercise-related factors (fatigue, hypoxia, AMP kinase, and cross-bridge cycling) on the activation of HSP72 transcription. HSP72 and HSP60 mRNA levels were assessed with real-time quantitative PCR; cytosolic Ca(2+) concentration ([Ca(2+)]cyt) was assessed with fura-2. Both fatiguing and nonfatiguing contractions resulted in a significant increase in HSP72 mRNA. As expected, peak [Ca(2+)]cyt remained tightly coupled with peak developed tension in contracting fibers. Pretreatment with N-benzyl-p-toluene sulfonamide (BTS) resulted in depressed peak developed tension with stimulation, while peak [Ca(2+)]cyt remained largely unchanged from control values. Despite excitation-contraction uncoupling, BTS-treated fibers displayed a significant increase in HSP72 mRNA. Treatment of fibers with hypoxia (Po2: <3 mmHg) or AMP kinase activation had no effect on HSP72 mRNA levels. These results suggest that the intermittent cytosolic Ca(2+) transient that occurs with skeletal muscle depolarization provides a sufficient activating stimulus for HSP72 transcription. Metabolic or mechanical factors associated with fatigue development and cross-bridge cycling likely play a more limited role.
authors: Department of Medicine, University of California, San Diego, La Jolla, California; and Department of Anesthesiology, Perioperative and Pain Medicine, Stanford University School of Medicine, Stanford, California cstary@stanford.edu.
authors: Creed M
authors: CM
authors: Stary
authors: Department of Medicine, University of California, San Diego, La Jolla, California; and.
authors: Michael C
authors: MC
authors: Hogan
mesh_terms: D000263:Adenylate Kinase / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D016257:Fura-2 / Q000378:metabolism; D050884:HSP72 Heat-Shock Proteins / Q000378:metabolism*; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D010805:Physical Conditioning, Animal / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism; D013449:Sulfonamides / Q000494:pharmacology; D014050:Toluene / Q000031:analogs & derivatives / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects / Q000502:physiology*; D014982:Xenopus laevis / Q000378:metabolism / Q000502:physiology
chemical_list: D050884:HSP72 Heat-Shock Proteins; C444880:N-benzyl-p-toluene sulfonamide; D012333:RNA, Messenger; D013449:Sulfonamides; D014050:Toluene; D000263:Adenylate Kinase; D002118:Calcium; D016257:Fura-2
keywords: ATP; Ca2+; HSP70; O2; RTq-PCR; exercise; fatigue; gene