Received February 21, 2005
Revised March 18, 2005
Accepted after revision May 13, 2005

¹ University of Aarhus

^* To whom correspondence should be addressed. E-mail: af{at}fi.au.dk.

	Abstract

Anoxia can lead to skeletal muscle damage. In this study we investigate whether an increased influx of Ca²⁺, known to cause damage during electrical stimulation, may be a causative factor in anoxia induced muscle damage. Isolated extensor digitorum longus (EDL) muscles from 4-wk old Wistar rats were mounted at resting length and were either resting or stimulated (30 min, 40 Hz, 10 sec on, 30 sec off) during 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 lead 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.

Key Words: Calcium, Hypoxia, Skeletal muscle