Ischemia/reperfusion-induced changes in intracellular free Ca²⁺ levels in rat skeletal muscle fibers – an in vivo study

Abstract

Accumulation of intracellular free calcium (Ca²⁺ _i) may play an essential role in the ischemia/reperfusion injury of skeletal muscle. Although it has been shown that Ca²⁺ _i levels significantly increase during ischemia/reperfusion, it is still a matter of debate whether Ca²⁺ _i increases during ischemia alone. It was the aim of this study to monitor the in vivo Ca²⁺ _i levels in the rat spinotrapezius muscle during ischemia of varying duration and reperfusion, using a ratiometric fluorescence technique, and to investigate the relationship between the postischemic flow patterns and Ca²⁺ _i, if any. The muscle was loaded with Indo-1/AM and imaged by a cooled digital camera. Pre- and postischemic tissue perfusion was assessed by means of an analogue camera. Our results show that short-term ischemia (5, 15 and 30 min) and subsequent reperfusion (60 min) does not alter Ca²⁺ _i homeostasis and that tissue perfusion promptly recovers after the insult. One or two hours of ischemia resulted in changes in Ca²⁺ _i levels, varying from preparation to preparation; increases in some and no changes in others. In these preparations three distinct flow patterns – normal, compromised and no-reflow – could be distinguished during the 60-min reperfusion. Our main conclusion is that in skeletal muscle Ca²⁺ _i levels may increase, the increase probably depending on the muscle fiber type exposed.