title: Anoxia induces Ca2+ influx and loss of cell membrane integrity in rat extensor digitorum longus muscle.
abstract: Anoxia can lead to skeletal muscle damage. In this study we have investigated whether an increased influx of Ca2+, which is known to cause damage during electrical stimulation, is a causative factor in anoxia-induced muscle damage. Isolated extensor digitorum longus (EDL) muscles from 4-week-old Wistar rats were mounted at resting length and were either resting or stimulated (30 min, 40 Hz, 10 s on, 30 s off) in the presence of standard oxygenation (95% O2, 5% CO2), anoxia (95% N2, 5% CO2) or varying degrees of reduced oxygenation. At varying extracellular Ca2+ concentrations ([Ca2+]o), 45Ca influx and total cellular Ca2+ content were measured and the release of lactic acid dehydrogenase (LDH) was determined as an indicator of cell membrane leakage. In resting muscles, incubated at 1.3 mM Ca2+, 15-75 min of exposure to anoxia increased 45Ca influx by 46-129% (P<0.001) and Ca2+ content by 20-50% (P<0.001). Mg2+ (11.2 mM) reduced the anoxia-induced increase in 45Ca influx by 43% (P<0.001). In muscles incubated at 20 and 5% O2, 45Ca influx was also stimulated (P<0.001). Increasing [Ca2+]o to 5 mM induced a progressive increase in both 45Ca uptake and LDH release in resting anoxic muscles. When electrical stimulation was applied during anoxia, Ca2+ content and LDH release increased markedly and showed a significant correlation (r2=0.55, P<0.001). In conclusion, anoxia or incubation at 20 or 5% O2 leads to an increased influx of 45Ca. This is associated with a loss of cell membrane integrity, possibly initiated by Ca2+. The loss of cell membrane integrity further increases Ca2+ influx, which may elicit a self-amplifying process of cell membrane leakage.
authors.affiliation: Department of Physiology, University of Aarhus, Ole Worms Allé 160, DK-8000 Arhus C, Denmark. af@fi.au.dk
authors.forename: Anne
authors.initials: A
authors.lastname: Fredsted
authors.forename: Ulla Ramer
authors.initials: UR
authors.lastname: Mikkelsen
authors.forename: Hanne
authors.initials: H
authors.lastname: Gissel
authors.forename: Torben
authors.initials: T
authors.lastname: Clausen
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000473:pathology; D004558:Electric Stimulation; D005260:Female; D006614:Hindlimb; D000860:Hypoxia / Q000473:pathology / Q000503:physiopathology*; D066298:In Vitro Techniques; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008297:Male; D018482:Muscle, Skeletal / Q000473:pathology* / Q000503:physiopathology*; D010100:Oxygen / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D014034:Toes
chemical_list: D007770:L-Lactate Dehydrogenase; D010100:Oxygen; D002118:Calcium