title: Intracellular sodium in mammalian muscle fibers after eccentric contractions.
abstract: The effect of eccentric contractions on intracellular Na(+) concentration ([Na(+)](i)) and its distribution were examined in isolated rat and mouse muscle fiber bundles. [Na(+)](i) was measured with either Na(+)-binding benzofuran isophthalate or sodium green. Ten isometric contractions had no significant effect on force (measured after 5 min of recovery) and caused no significant change in the resting [Na(+)](i) (7.2 +/- 0.5 mM). In contrast 10 eccentric contractions (40% stretch at 4 muscle lengths/s) reduced developed force at 100 Hz to 45 +/- 3% of control and increased [Na(+)](i) to 16.3 +/- 1.6 mM (n = 6; P < 0.001). The rise of [Na(+)](i) occurred over 1-2 min and showed only minimal recovery after 30 min. Confocal images of the distribution of [Na(+)](i) showed a spatially uniform distribution both at rest and after eccentric contractions. Gd(3+) (20 microM) had no effect on resting [Na(+)](i) or control tetanic force but prevented the rise of [Na(+)](i) and reduced the force deficit after eccentric damage. These data suggest that Na(+) entry after eccentric contractions may occur principally through stretch-sensitive channels.
authors.affiliation: Department of Rehabilitation Sciences, Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China.
authors.forename: Ella W
authors.initials: EW
authors.lastname: Yeung
authors.forename: Heather J
authors.initials: HJ
authors.lastname: Ballard
authors.forename: J-P
authors.initials: JP
authors.lastname: Bourreau
authors.forename: David G
authors.initials: DG
authors.lastname: Allen
mesh_terms: D000818:Animals; D001572:Benzofurans; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004988:Ethers, Cyclic; D005456:Fluorescent Dyes; D005682:Gadolinium / Q000494:pharmacology; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism*; D007473:Ion Channels / Q000037:antagonists & inhibitors / Q000378:metabolism; D007537:Isometric Contraction / Q000187:drug effects / Q000502:physiology; D051379:Mice; D018613:Microscopy, Confocal; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000502:physiology*; D009930:Organic Chemicals; D009994:Osmolar Concentration; D010042:Ouabain / Q000494:pharmacology; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors; D014018:Tissue Distribution
chemical_list: D001572:Benzofurans; D004791:Enzyme Inhibitors; D004988:Ethers, Cyclic; D005456:Fluorescent Dyes; D007473:Ion Channels; D009930:Organic Chemicals; C098118:sodium green; C061665:sodium-binding benzofuran isophthalate; D010042:Ouabain; D012964:Sodium; D005682:Gadolinium; D000254:Sodium-Potassium-Exchanging ATPase