title: Interactions between intracellular calcium and phosphate in intact mouse muscle during fatigue.
abstract: Fatigue was studied in intact tibialis anterior muscle of anesthetized mice. The distal tendon was detached and connected to a force transducer while blood flow continued normally. The muscle was stimulated with electrodes applied directly to the muscle surface and fatigued by repeated (1 per 4 s), brief (0.4 s), maximal (100-Hz stimulation frequency) tetani. Force declined monotonically to 49 ± 5% of the initial value with a half time of 36 ± 5 s and recovered to 86 ± 4% after 4 min. Intracellular phosphate concentration ([P(i)]) was measured by (31)P-NMR on perchloric acid extracts of muscles. [P(i)] increased during fatigue from 7.6 ± 1.7 to 16.0 ± 1.6 mmol/kg muscle wet wt and returned to control during recovery. Intracellular Ca(2+) was measured with cameleons whose plasmids had been transfected in the muscle 2 wk before the experiment. Yellow cameleon 2 was used to measure myoplasmic Ca(2+), and D1ER was used to measure sarcoplasmic reticulum (SR) Ca(2+). The myoplasmic Ca(2+) during tetani declined steadily during the period of fatigue and showed complete recovery over 4 min. The SR Ca(2+) also declined monotonically during fatigue and showed a partial recovery with rest. These results show that the initial phase of force decline is accompanied by a rise in [P(i)] and a reduction in the tetanic myoplasmic Ca(2+). We suggest that both changes contribute to the fatigue. A likely cause of the decline in tetanic myoplasmic Ca(2+) is precipitation of CaP(i) in the SR.
authors.affiliation: School of Medical Sciences and Bosch Institute, University of Sydney, Sydney, NSW 2006, Australia. david.allen@sydney.edu.au
authors.forename: D G
authors.initials: DG
authors.lastname: Allen
authors.forename: E
authors.initials: E
authors.lastname: Clugston
authors.forename: Y
authors.initials: Y
authors.lastname: Petersen
authors.forename: I V
authors.initials: IV
authors.lastname: Röder
authors.forename: B
authors.initials: B
authors.lastname: Chapman
authors.forename: R
authors.initials: R
authors.lastname: Rudolf
mesh_terms: D000818:Animals; D001831:Body Temperature / Q000502:physiology; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D004558:Electric Stimulation; D007090:Image Interpretation, Computer-Assisted; D008164:Luminescent Proteins; D009682:Magnetic Resonance Spectroscopy; D051379:Mice; D008810:Mice, Inbred C57BL; D008856:Microscopy, Fluorescence; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000098:blood supply / Q000502:physiology* / Q000648:ultrastructure; D010710:Phosphates / Q000378:metabolism / Q000502:physiology*; D011993:Recombinant Fusion Proteins; D012039:Regional Blood Flow / Q000502:physiology; D012519:Sarcoplasmic Reticulum / Q000502:physiology / Q000648:ultrastructure
chemical_list: D008164:Luminescent Proteins; D010710:Phosphates; D011993:Recombinant Fusion Proteins; C492603:Ycam-2 fluorescent protein; D002118:Calcium